trimaran aka

• You are here
• Everything Explained.Today
• A-Z Contents
• Polynesian multihull terminology

Polynesian multihull terminology explained

Polynesian multihull terminology , such as "ama", "aka" and "vaka" (or "waka") are multihull terms that have been widely adopted beyond the South Pacific where these terms originated. This Polynesian terminology is in common use in the Americas and the Pacific but is almost unknown in Europe, where the English terms "hull" and "outrigger" form normal parlance. Outriggers, catamaran s, and outrigger boat s are a common heritage of all Austronesian peoples and predate the Micronesian and Polynesian expansion into the Pacific. They are also the dominant forms of traditional ships in Island Southeast Asia n and Malagasy Austronesian cultures, where local terms are used. [1] [2]

See also: Waka (canoe) and Outrigger boat . The term vaka or waka means "boat" or "canoe" in most Polynesian languages. It comes from Proto-Austronesian *abaŋ, meaning "ship" or "canoe". Cognate s in other Austronesian languages include Ivatan Awang , Tagalog and Visayan bangka , Malay wangkang , and Fijian waqa . [3]

"Ama", "aka" and "vaka"

The term ama is a word in the Polynesian and Micronesian languages to describe the outrigger part of a canoe to provide stability. Today, among the various Polynesian countries, the word ama is often used together with the word vaka ( Cook Islands ) or waka ( Māori ) or va'a ( Samoa Islands , Tahiti ), cognate words in various Polynesian languages to describe a canoe.

The Polynesian term vaka is the main hull , the ama is the outrigger, and the aka or iako (Hawaiian) is the support connecting the two (not three) hulls. The term ama and aka have been widely applied to modern trimaran s.

In modern sailing, the term is sometimes used to refer to the outrigger on double-outrigger canoes ( trimaran s), or the two sections of a catamaran . However, calling the two sections of a catamaran by the word ama is not technically correct since they are of equal size. A catamaran is technically a wa'a wa'a or double canoe connected by an aka . [4]

On a proa, the ama may provide lift or ballast , depending on whether it is designed to be used to leeward or windward ; on a trimaran it is designed primarily to provide lift. There are many shapes of ama; those used in proa s are generally laterally symmetric, as the proa is designed to sail with either end forwards, while trimaran ama are one-directional and may have no axis of symmetry.

The most advanced ama are composed of highly curved surfaces that generate lift when driven forward through the water, much like an airplane wing. This lift may be directed to the windward, used to counter slipping to leeward , or may be oriented vertically to counter heeling forces from the sailing rig . These highly curved structures are much more difficult to manufacture than traditional ama and are therefore more expensive. The Bruce foil is an example of a type of leeboard often attached to an ama to assist in producing lift.

Use of the term in other cultures

Even though double-outrigger ships ( trimaran s, sometimes informally referred to as "proas" historically) of other related Austronesian groups in Island Southeast Asia , Island Melanesia , and Madagascar didn't reach Polynesia or Micronesia, they may also sometimes use Polynesian terminology in modern times, especially when used in sport sailing. [5]

The US Navy tri-hull Independence -class littoral combat ship refers to their outboard hull sections as an "Amah". "An Amah tip is the leading edge of the all-aluminum, trimaran-type vessel’s outrigger, or amah, and is more than seven feet across and weighs 850 pounds." [6]

• Polynesian navigation
• Bangka (boat)
• Waka (canoe)
• Outrigger canoe
• Hōkūleʻa
• Beheim . B. A. . Bell . A. V. . Inheritance, ecology and the evolution of the canoes of east Oceania . Proceedings of the Royal Society B: Biological Sciences . 23 February 2011 . 278 . 1721 . 3089–3095 . 10.1098/rspb.2011.0060. 21345865 . 3158936 .
• Hornell . James . Was the Double-Outrigger Known in Polynesia and Micronesia? A Critical Study . The Journal of the Polynesian Society . 1932 . 41 . 2 (162) . 131–143.
• Dempwolff . Otto . Vergleichende Lautlehre des austronesischen Wortschatzes . Zeitschrift für Eingeborenen-Sprachen . 1934–1938 . Special Publication . 15,17,19.
• Web site: Story: Canoe navigation - Waka – canoes' . Rāwiri Taonui, Te Ara . The Encyclopedia of New Zealand . 4 March 2009.
• Web site: The Tridarka Raider . 2007-10-30. https://web.archive.org/web/20071020045916/http://www.tridarkaraider.com/. 20 October 2007. dead.
• Alcoa Provides Aluminum Amah Tips to Austal for Littoral Combat Ship USS Jackson (LCS 6) . 16 April 2012 .

This article is licensed under the GNU Free Documentation License . It uses material from the Wikipedia article " Polynesian multihull terminology ".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2024, A B Cryer, All Rights Reserved. Cookie policy .

Professional BoatBuilder Magazine

Folding multihulls.

By John Marples , Jan 28, 2023

Folding multihulls and their beam-reduction strategies.

A Farrier 33R trimaran with amas folded and secured on a road-legal trailer exem- plifies the advantages of adjustable- beam multihulls, which are easy to trans- port and store out of the water.

“I’ll be surprised if you can find space in the harbor for that thing,” I heard him say as my new 37 ‘ (11.3m) trimaran was about to be launched. I hadn’t given it much thought, but now this legitimate question was raised, and where to moor was the next issue at hand. Space, particularly width of a slip, becomes the limiting requirement. But then, space also is one of the attractive features of multihulls—deck space to move around on, free from the confines of the cockpit.

Step aboard any multihull and it is obvious how much real estate they offer. Even small models seem expansive. The beam of the typical catamaran is half its length, and trimarans are even wider, sometimes as wide as they are long. Aside from increasing space, beam also boosts stability without adding ballast. The early Pacific Islanders created these form-stable craft for fishing and interisland commerce and voyaging where natural island harbors were few, so the boats had to be light enough for crew to carry them up the beach. Today’s modern multihulls are still lighter than contemporary monohulls, but the larger ones preclude the option of dry sailing them from the beach. They require more marina space than monohulls, and the limited number of slips to accommodate them can be a problem. As someone once put to me, “Multihulls have a poor ‘stacking factor.’”

With catamarans and trimarans becoming more popular, they demand mooring solutions. Some marinas offer shallow-water slips to multihulls, typically at the inboard ends of docks, next to the seawall, because multihulls either have shallow keels or retractable boards. Some marinas also designate the end ties as multihull slips in areas not used for transients. Even though these boats protrude farther into the channel than monohulls, the extra space their beam occupies is relatively small. With multihulls crowding waiting lists for marina slips, builders were prompted to consider folding systems to “improve their stacking factor.”

Without ballast, smaller multihulls up to about 30 ‘ (9.1m) can be dry-stored on a trailer, and most launch ramps easily accommodate over-width boats. If the boat’s beam can be reduced to the legal highway width of 8.5 ‘ (2.6m), the owner can store the boat at home. Today, folding trimarans and catamarans are common sights on trailers in storage yards and backyards. Various folding systems have evolved to support this need, especially for the backyard builder. Some beam-reduction systems allow the boats to be folded and stored in the water in conventional-size marina slips, while other systems facilitate efficient storage or provide street-legal trailering.

Folding Systems

Basic folding systems are separated into several categories:

• take-apart akas, the simplest beam-reduction method
• telescoping akas (sliding beams)
• simple horizontal hinge
• complex horizontal hinge systems
• vertical hinges (swing wing)
• complex swing wing

The following overview of folding systems illustrates how these mechanisms work. It is not intended to be an exhaustive listing of available folding designs. I’ll address two-hull boats (catamarans and proas) first, followed by trimarans. Each type has its challenges and advantages. All are separated into two more categories: transportable boats and trailerable boats. The characteristic distinguishing between them is the time and effort required to launch, starting from an on-the-trailer folded condition. Trailerable implies the possibility of daily launching, requiring less than an hour from trailering to sailing. Transportable denotes a road-legal trailer package but with a longer assembly time to sail away. It might even take more than one trailer load, and considerable assembly time. Legal width in this category could extend to 10 ‘ (3m) wide if OVERSIZE LOAD signs are used (consult local laws). Transportable boats usually require seasonal transport with storage in the water during sailing season and dry storage in the winter. Both categories benefit from the ability to “go to weather at 65 mph” to reach any suitable launching site, even hundreds of miles from home. This opens the possible sailing venue to any water body with a launch ramp and road access, and some trailerable and transportable boats can be delivered anywhere in the world in standard shipping containers.

Catamarans and Proas

The WindRider 17′ trima- ran’s telescoping tubular akas are secured with pins

Hobie Cats and other beach cats are familiar sights around lakes, beaches, and harbors. They are usually built to 8 ‘ (2.4m) beam and do not need folding systems. The 19 ‘ (5.8m) Tornado class catamaran at 10 ‘ wide uses a side tilt-up trailer to reduce beam. Larger catamarans needing folding systems have greater challenges than trimarans of the same length, for a few reasons: The hulls are normally bigger (and heavier) than amas for the same length trimaran; the mast is stepped on the center of an aka, midway between the hulls, which means the aka must be extra strong; and there is no easy means of supporting the hulls while the beam is being expanded to the sailing position, requiring that the trailer have an expanding-beam function. As a result, folding systems are less common on cats and are usually of three types:

• folding akas along the centerline or to a center pod
• telescoping akas
• take-apart akas

On this Wharram cat, the akas are securely lashed into “deck alleys.”

Designers have used telescoping akas, but production boats generally avoid the associated complexity and cost. The mechanically straightforward take-apart feature has successfully been used by many boats, like the 27 ‘ (8.2m) Stiletto Cat and others. Generally, the assembly of these boats takes some time and muscle, which relegates them to the transportable category. Stiletto Cat advertising suggests a four-hour setup time, but in reality, it is much longer. All the James Wharram–designed catamarans up to 63 ‘ (19.2m) are held together with rope lashings and can be dismantled for transport. The required time and effort are generally proportional to the length of the boat.

Note that the Gougeon 32 ‘ (9.7m) sailing catamaran is unique, at 8 ‘ wide, without folding capability but with a water ballast system to make up for the lack of form stability.

The large main hull of a typical smaller trimaran offers a larger interior space than a comparably sized catama ran, a deep footwell in the cockpit for comfortable seating, and a folding system for trailering with the amas connected to a well-supported main hull. In addition, the mast is stepped on the main hull, with the headstay attached to the bow, not to the akas.

Trailerable trimarans come in all sizes to about 32 ‘ long, with transportable designs somewhat longer. The latter types tend to have larger interior spaces and less complex connectives. To a certain extent, manufacturers were willing to add cost to the folding system to reduce setup time. Folding capability on or off the water also adds to the design challenges.

Take-Apart Aka Systems

This is the least expensive method and easiest to achieve for the home builder or the manufacturer. The akas may be built-up wood box beams or tubular metal. Each beam is secured to the hulls by through-bolts, bolted straps, plug-in sockets, or lashings. Tubular aluminum beams are the lightest but most expensive. Regardless of attachment method, the hulls must be supported in their respective positions for the akas to be installed. In small vessels, this can be an abbreviated procedure, but larger vessels will require a special trailer to hold the disconnected amas while on the road.

The Chesapeake Light Craft 15′ single outrigger canoe akas lash into saddles on both hulls.

Telescoping Aka Systems

The telescoping option is limited to boats where the total stack-up width and length dimensions of the hulls and fully retracted akas do not exceed the legal road limits. The WindRider 17 is a good example. The boat is supported on “high bars” on the trailer, leaving the amas free to be moved in or out. The simplicity of the akas and trailer-support system reduces cost and launching time.

In larger vessels, this system has been applied to reduce width for storage in marina slips. For these boats, the sliding system is large and complex, usually requiring some sort of power to make the telescope slide. Because the sliding mechanism requires a small clearance between the sliding members, the akas will move slightly during sailing, which is difficult to avoid.

The 1970s-vintage Telstar 26 features a simple hinge-down system with a bolted con- nection on deck and a bolted strut below.

Simple Horizontal Hinge Systems

Early trailerable trimaran designs often incorporated a simple hinged beam-reduction system to fold both sides down. Boats to about 25 ‘ (7.6m) with a 16 ‘ (4.9m) beam could be made to fold to 8 ‘ . At the ama end, lifting the hull, sometimes with attached wing deck, could require substantial muscle or a mechanical lift. Even for smaller boats this task may be beyond one person’s capability. Normally, bolts and plates between the members secure the hull for sailing. On the Searunner 25 and Constant Camber 26 (7.9m), double-hinged tubes are bolted to tangs on the main hull.

The Searunner 25 trimaran has a hinge mechanism on its metal-tube A-frame akas that secures with bolts at both ends.

Commonly, simple hinge systems require that the main hull be positioned rather high on the trailer so the amas clear the trailer wheels beneath. A disadvantage is that the trailer must be submerged more deeply than usual for the boat to float off. Compared to the Telstar system, the Searunner 25 offered some improvement by positioning the hinge point at the top of the cabinside, raising the folded ama slightly.

Complex Aka Hinge Systems

A complex system for folding multihulls, much like a garage door lift linkage, was developed and patented by Ian Farrier for his trailerable trimaran designs. It allows one person to fold or unfold the boat while it’s afloat. Before launching, the mast is stepped and secured with lower stays. Note that folded storage in the water for long periods is not practical because the immersed ama’s topsides will gather marine fouling. In addition, the arrangement of the support linkage arms has a very shallow angle with the aka, causing them to be highly stressed, which adds significant weight and cost.

Unfolding it requires help from friends.

A complex folding system I developed has only four attachment bolts and a wide-angle strut brace. It is very light but requires folding prior to launching. It relies on a simple roller dolly on a beam attached to the trailer to support the ama during folding and unfolding.

Swing-Wing Systems

In-water storage of folding trimarans is generally limited to swing-wing designs, where the hulls all float on their respective waterlines, either folded or unfolded. Many variations have been used in production boats, and among the most successful is the Quorning-designed Dragonfly. It has hinged arms supported by a “waterstay”— a diagonal cable under the arm to counteract cantilever aka loads. The outer end of the arm, on the ama deck, pivots on a single pin. The waterstay becomes slack when the boat is folded, leaving only the hinge to support the ama in the folded configuration. I’ve seen one folded boat that was damaged while moored at the dock in strong harbor waves when the ama climbed onto the dock. Swing-wing designs stored in the water must provide strong vertical support for the ama in the folded condition

A swing-wing aka system on the Borg Quorning–designed Dragonfly 32 is further supported by a waterstay when rigged for sailing. The akas can be adjusted in and out while in the water and for storage at the dock.

The main challenge of the swing-wing system is to get all the pivot axes parallel because they must rotate about 90° without binding. If there is any depth to the structure, this accuracy is critical, as the pins or pivot axles could be quite long, so even a small inaccuracy will make the system difficult to assemble, let alone pivot smoothly.

Folding Multihulls with Flat Swing-Wing Akas

The most basic swing-wing system is the flat aka configuration developed by Jim Brown. He avoided the need for perfect parallel alignment of all hinge axes because the beams are not very thick, and the pivot-pin holes can have additional clearance. For the swing system to operate without binding, spacing of the pivot points must be identical on all the swing arms. The system’s downside is strength, because the aka must support all the heeling loads in a relatively narrow beam. For some boats, a waterstay may need to be added to increase cantilever strength and reduce deflections when sailing.

The Seaclipper 16 flat swing- wing akas are made from common dimensional lumber and pivot using steel bolts.

A logical improvement in strength for swing arms is to add a truss, with triangulated strength that will easily bear all the heeling loads from the ama. Here again, it is essential that pivot axes be in perfect alignment to avoid binding. To my eye, open trusses in sleek yachts are never beautiful, but they offer higher strength for lower weight.

Complex Swing-Wing Systems

If the akas are not flat along their full length, it is more difficult to achieve a smoothly pivoting system. My latest boat, Syzygy (pronounced, sis-a-gee), is a case in point. Flat akas offer little variation in styling—flat is flat. To add underwing clearance and more attractive aesthetics, many designers favor the arched aka. This configuration allows the aka to approach the ama hull from above and connect through the deck for more usable immersion of the ama buoyancy, and to keep the aka above the wavetops.

This system has arched akas with an upward angle (dihedral) as they extend from the main hull and descend with a smooth curve onto the ama deck. The pivot axis must also be inclined, normal to the surface, to allow it to pivot. To make life simple, the vertical centerline of the ama is inclined inboard at the top by the same amount, which aligns all the pivot axes with the ama vertical centerline. If the beam is level fore-and-aft, when the ama is folded inboard, it is positioned rather low, due to the arch. To compensate, the akas must be given a negative angle of attack to make the folded ama arrive in the same position as a simple flat aka system. It’s a good challenge for any boatbuilder to get it right and a good use of a digital level. The angles in Syzygy were 8° dihedral, and a nega tive 5° angle of attack. The aka pivot surfaces must be perfectly parallel on both ends—at the inboard aka pivots and the ama deck pivot tables.

Jan Gougeon designed and built strings, a 40′ swing-wing catamaran with carbon- tubular-truss swing akas built over foam mandrels.

A late iteration of the Telstar 26 became the Telstar 28 with a vertical-axis swing-wing system. This production boat is no longer manufactured but was unique for its faired wing and attempt to hide the folding system from view. It also featured an electric linear drive to fold/unfold the heavy akas.

For transporting folding multihulls on the highway, road trailers must have some specific attributes to properly support the hulls. Most models use transverse cradle supports under the hull at major interior bulkhead positions. It is important to install bow guides on the trailer to get the hull to settle in exactly the right place when retrieved from the water. Rollers beneath the hull are not recommended, as they tend to distort it and potentially cause damage. The amas require enough support so the folding mechanism is not carrying the load when being towed.

For swing-wing boats, there is a significant change in the center of gravity between folded to unfolded configurations. Normally, the amas swing back when folded and swing forward for the sailing position. If the trailer has the proper tongue weight for towing on the hitch with the boat folded, the weight will increase when unfolded. For trailers with telescoping tongues, tongue design must accomodate that weight; otherwise, the extended tongue may bend severely during launching or retrieval.

Homebuilt wooden trailers are popular for these specialized boats, and some designers provide plans for them. Without much metal in them, they will probably float, which sometimes leads to difficulty at launching. Adding some steel channel to the bunks can solve that. However, floating is not an undesirable feature if a trailer floats level but is submerged enough to maneuver the hull into the bunks, and the hull settles into the right place automatically. Floating trailers also never run off the end of the ramp.

Conclusions

There’s truth in the humorous claim that “the new family yacht has to look good behind your SUV.” But while many of the latest small boats are daysailers, folding multihulls have expanded the trailerable and transportable boat size to include those with weekend cruising capability, up to about 32 ‘ . As we’ve seen, those essential folding or retraction mechanisms are not simple and must be carefully designed and engineered, even by the home builder. But for owners of these boats, seasonal storage and slip availability are no longer problems. And the overall reduction in total cost can bring owning a boat within reach for many more people. What’s not to like about that?

About the Author: John Marples has designed, built, and rigged many sail- ing vessels. His portfolio includes doz- ens of wood-epoxy composite sailing and power multihulls to 110′ (33.5m). He operates Marples Marine , a multihull design and engineering firm in Penobscot, Maine

Dieter Loibner | Professional BoatBuilder Magazine

Nomenclature

Multihull designers have developed some useful, specific names for components, mostly derived from the Pacific Islander language.

Aka (ah-kah) refers to the crossbeam structure of any multihull. Designers used to call them “cross-beams,” but writing that on hand-drawn plans took up too much space and time, so this shorter Polynesian name became the standard.

Ama (ah-mah) is the Polynesian name for the outer hull of a trimaran or proa. They were formerly named “floats” or “outer hulls” (never pontoons), but again, ama is shorter.

Vaka (vah-kah) is the Polynesian name for the main (largest) hull of a trimaran or proa. Since it can be confused with the other names and is not very descriptive, most designers have opted for the term main hull.

Waterstay is a diagonal stay, metal or synthetic rope, below the aka, between the main hull near the waterline and aka near its outboard end. This stay counteracts the upward load from ama buoyancy when the ama is immersed.

—John Marples

The Crossbeam (Aka) Structure 

T he essential function of any crossbeam (aka) system on a multihull is to structurally connect the hulls in a way that resists all the forces generated when sailing. Heeling forces from lift on the sails must be transferred to the leeward hull by the aka structure. The forces on the akas are complex, composed of cantilever bending due to heeling loads, twisting of the structural platform, and horizontal bending caused by drag from the ama’s forward motion through the water. The heeling force, resisted by the buoyancy of the ama, pushes up, causing cantilever bending loads in the akas similar to the forces on an airplane wing. Torsion is created when the sails’ lift pushes the leeward ama bow down, while the shrouds supporting the mast pull the weather-side ama stern up. Drag from the leeward ama tries to bend the akas toward the stern, and forces from the windward shroud tend to pull the aka forward as well as up. These forces all act together at the attachment points on the hulls. In most cases, torsion is resisted by the tubular hull and cabin structure itself. Heeling is countered by the cantilever strength of the aka beams and is sometimes strengthened by diagonal waterstay cables beneath. Drag forces can be resolved by the fore-and-aft strength of the akas or by adding diagonal cables between the akas. Each folding system must accommodate these loads through all the pivoting components in the structure.

Of key interest in aka design are the loads imposed on the ama hulls by the seaway when sailing to windward. These hulls are subject to significant loads on the outboard sides. The windward ama is pummeled by wavetops, and the leeward ama is pushed sideways due to leeway. Since the aka system is characteristically attached through the ama deck, these forces are trying to rotate the ama keel inboard, toward the main hull, in either case. The same is true for catamarans, concerning the aka loads where they emerge at the hull inboard sides. These loads can be calculated to estimate the strength required for any configuration and should be part of the design’s stress analysis. If centerboards or daggerboards are located in the amas, those rotating forces are significantly increased.

Of further interest in swing-wing designs is the clearance between pins and brackets in vertical pivot mechanisms. When sailing, the forces at the hinge pins can change from positive to negative repetitively, creating noise and wear. The wear will eventually elongate the holes, reduce pin diameter, and become a maintenance problem. Designs like the flat wing can be tightened to eliminate movement, which will eliminate wear. Amas with waterstays tend to put the akas in compression and stop the vertical deflection that would be normally carried through the hinge pins. In that case, the pins would be loaded in only one direction and not be subject to cyclic ± loads. —J.M.

Read more Construction , Design articles

• Infusing a Workboat Hull with Elium

Recyclable thermoplastic resin and a crew of trainees are put to the test building a commercial fishing boat at DJ Marine in Pointe-Sapin, New Brunswick.

• Counting Carbon with LCA

A yacht designer and experienced builder of composite boats test-drives life cycle assessment software customized for the marine trades.

• From Langan Design Partners, a Classic Cutter

Designing, engineering, and building sailing yachts 90′ (27.4m) or more in length once was common in the U.S. It’s happening again at Rockport Marine in Maine: Project Ouzel, a 95′… Read more »

Recent Posts

• AIRMAR Achieves World’s First OneNet Product Certification
• Isobel Combines Classic Looks and Modern Tech
• Companies (91)
• Construction (115)
• Design (168)
• Drawing Board (11)
• Education (29)
• Environment (18)
• Events (22)
• Materials (55)
• Obituary (18)
• People/Profiles (49)
• Products (18)
• Propulsion Systems (35)
• Racing (17)
• Repair (37)
• Rovings (326)
• Short Cuts (3)
• Sponsored Partner News (19)
• Systems (80)
• Task Sheet (1)
• Uncategorized (28)
• Wood to Glass (8)

ProBoat.com Archives

What is a Trimaran Boat? Its Terminology, History,

Updated: July 31, 2024     9 Minutes Read

Do you want to know about Trimaran? If yes, you are in the hundred percent right place. A trimaran, also known as a double-outrigger, is a type of multi-hulled boat that features a main hull and two smaller outrigger hulls or floats that are attached to the main hull with lateral beams. Most modern trimarans are used as sailing yachts for racing or recreation, and others are warships used by the navy and ferries. 

The hull design of the Trimaran comes from the double-outrigger hulls of the Austronesian culture of maritime southeast Asia, especially from Eastern Indonesia and the Philippines, where it was used in fishing boats . And the design of double-outriggers originated from single-outrigger boats and old catamarans. 

Terminology

The term “Trimaran” originated from the combination of tri and maran. The tri means three, and maran is basically derived from catamaran boat s. It’s believed that Trimaran was created by Victor Tchetchet, who is basically a Ukraine-based modern multi-hull designer. A trimaran is featured with a main hull and two smaller outrigger floats on either side, attached by crossbeams. In Polynesian terms, the main hull is generally considered “vaka, ” while each float is referred to as “ama,”  and the connectors that connect them together are usually known as “aka.”  However, trimarans are not considered traditional Polynesian boats; Polynesians generally use single-outrigger canoes and catamarans.

Ownership Costs for Trimarans

The ownership cost of Trimarans widely differs according to their model, brand, size, and quality of construction. On average, their ownership price starts at $100,000 and goes up to a million dollars. If you want to determine how much you can afford, use our boat loan calculator .

The first Trimaran, or double-outrigger boat, was designed by the Austronesians and is still most loved by the fishermen of maritime southeast Asia . This double outrigger was improved from the oldest single outrigger boats to resolve the problem of boats tipping over when turning into wind. However, double outriggers did not get populated among austersians in Polynesia and Micronesia, where people use catamarans and single outriggers.

The warships with double outriggers, such as Karakoa, Kora Kora, Lanong, and Borobudur, were broadly used in maritime southeast Asia for many years. These vessels were also called proas by Europeans during the colonial era. And proas is basically a broad term that includes native ships and single-outriggers. 

20th Century 

Recreational sailing with trimarans and catamarans gained popularity in the 1960s and 1970s. Victor Tchetchet, who was basically a Ukrainian immigrant to the US, manufactured two Trimarans by using marine plywood. These trimarans were around 24 feet, or 7.3 meters, longer in length. Then, in the 1950s and 1960s, Arthur Piver designed new plywood kit trimarans, which were heavy and not suitable for seas compared to modern models, but still a few achieved the success of crossing oceans. Several of their additional models, including Chris White, Derek Kelsall, Ed Horstman, Richared Newik, John Marples, Norman Cross, Jim Brown, and Jay Kantola, were built using contemporary construction methods, which basically improved the performance and safety of Trimaran cruisers.

After that, many homebuilders and new boating companies started making trimaran boats. Most of their models were 19–36 feet, or 5.8–11 meters, longer in length and were widely used as “day-sailers’ ‘. They were also trailerable by boat trailers, and their examples include original Ferrier and Corsair folding trimarans like the F-27 Sport Cruiser and the original John Westell and Swing-wing folding trimaran.

Modern Trimarans were constructed in the west and were significantly distinguished from their counterparts. They use a Bermuda rig sail plan instead of unique sails like crab claw or Tanja. These trimarans are also larger and have bigger floats, which provides them with more buoyancy than outrigger canoes . However, these floats may create drag when they get too wet, and their level of immersion shows when to reef. In respect of performance, an objective comparison by Doran in 1972 proved that the traditional double-outrigger vinta of the Philippines and the single-outrigger WA of the Caroline Islands are still amazing at sailing against wind and speed compared to modern trimarans.

Competition And Records

There are many competitions, and world records exist for Trimaran vessels. Thomas Coville is also one of them, having set the world record for solo sailing all over the world for around 49 days and 3 hours. This world record was made by Sodebo Ultim Trimaran and completed on December 25, 2016.

Before Thomas’ world record, in February 2005, a record was held by a British sailor, Ellen MacArthur , in which she spent around 71 days circling the world. After that, on January 20, 2008, a Frenchman broke the Ellen MacAuthers record by spending just 57 days, 13 hours, 34 minutes, and 6 seconds in Trimaran by exploring the planet.

Additionally, between December 2016 and January 2017, Francis Joyon and his five crew members set a new record for the fastest maritime circumnavigation by fishing the journey in just 40 days, 23 hours, 30 minutes, and 30 seconds. Their standard speed was around 26.85 knots, or 30.71 MPH, and they covered almost 48,915 kilometers, or 26,412 nautical miles. 

In 2020, the same Trimaran completed the race from Hong Kong to London in an impressive 32 days. This time is about one-third of the first record, which was made in 2005. 

 Trimaran Ships

High-speed ferries.

High-speed ferries are managed by specific rules. These rules are applied to those ferries that are used for international journeys lasting less than four hours and cargo ferries that are used for almost eight hours from a safe harbor. Private berths or sleeping areas are not available in these vessels, but every passenger must be given a seat.

The demand for high-speed ferries increased after the 1970s. In the 2000s, there were only two Australian companies, “ Incat and Austal,” building large and high-speed ferries. Incat was busy making catamarans, which basically move forward by cutting water waves, and Austal was an expert in making high-speed trimarans.

In 2010, Austal manufactured a 120-meter ferry called Hull 270, which was sold to Condor Ferries in 2015. After that, Condor Ferries changed its name to HSC Condor Liberation for visits to the Channel Islands. The interest in Trimaran ferries increased in 2017 when Fred. Olsen Express bought two 118 Trimarans from their island routes that were called Bajamar Express and Bañaderous Express . In 2018, a Japanese company also purchased an 83-meter ferry. 

Naval ships

The first and modern use of Trimaran hull design in navy ships was with the RV Triton . RV Triton is basically a research vessel for the Royal Navy and was manufactured with a Trimaran hull to test the hull’s visibility. This vessel has been used by the Australian customs and border protection service since 2007. 

The Indonesian navy’s first stealth Trimaran, the 63M carbon fiber composite Trimaran fast missile boat, was discovered in 2012. This was manufactured by North Sea boats with modern stealth technology and a wave-piercing Trimaran hull, but its design was made by New Zealand naval architects, LOMOCEAN Marine . Unfortunately, this vessel was destroyed by an engine room fire shortly after its launch. 

After that, the 43-meter ocean Eagle Trimaran was built by the Nigel irens and is based on the ocean adventure concept, which provides coastal protection for Mozambique.

Folding Trimarans

Some of the boat manufacturers build fold-able trimarans, which means these trimarans have floats that can be flooded near the main hull. Their foldable feature basically makes them easily trailerable by boat trailers and allows them to easily fit in a typical monohull space in a marina. There are various mechanisms used to store a folding trimaran or amas outrigger, which include demountable fixed tubes that are assembled before launching, telescoping tubes, and a hinge and latch system that allows the amas or foldable trimaran to fold over the main hull to reduce width for trailering. In addition, some Trimarans have a vertical folding system, which basically lifts the floats upward and over the main hull. On the other hand, a few Trimarans feature horizontal articulation, which moves the floats forward or backward at the same level as the hull, or horizontal folding, which folds the floats towards the main hull. These modern techniques for folding trimarans basically make them easier to trailer and transport; that’s why many people use them as sailing trimarans.

Folding Trimaran Safety Features 

There are many features of folding trimarans that assure safer journeys than other boat types . Trimarans have special compartments for protection from sinking, easy-to-reach controls, a system of prevention from collisions, covered and safe cockpits, and fast-draining holes. However, a capsized Trimaran may be harder to flip back, and some may also get damaged. But the new Trimarans are specially designed to easily turn back when capsized. To stay safe, it’s better to reduce sail power in strong winds and use special features like netting and water-shedding decks to protect a capsized Trimaran. 

Benefits of Trimaran Boats

The Trimaran configuration is suitable for both navy ships and commercial ferries. An Australian boat manufacturer company, “ Austal ” conducted the study to increase the advantages of Trimaran ships, catamarans, and monohulls and find out the ideal positioning of outer hulls to minimize wave resistance and power consumption when operating at high speeds with heavy payloads of almost 1,000 tons. This change made Trimarans more efficient, reduced motion sickness, and improved roll and lateral force stability, especially in rough seas. These features of Trimarans made it the best choice for warships and passenger ferries. Some of the other advantages of trimarans are: 

• Trimarans with high-quality construction can move smoothly and quickly in seas, even with heavy loads.
• They are basically made to be stable and versatile, and they roll well in rough seas.
• They help to prevent motion sickness.
• They can be manufactured in larger models.
• Trimarans can carry low-density cargo or passengers and can go at around 40 knots of speed. 

Disadvantages of Trimarans

• Trimarans are mostly tough and pricey to build.
• They are usually challenging to dock because of their design and size. 
• They may also not be suitable for carrying heavy cargo and passengers. 
• Their interior space is mostly less than that of Catamarans. 

I'm Raunek Kantharia, a professional marine engineer. I'm also a marine writer who joined the Marine Insight website in 2010 as an expert marine writer. I managed the Marine Insight website. After that, I wrote many articles for magazines and websites. But now, I write for readboating.com. I share my insights and knowledge from my own experience.

Please Write Your Comments

Boating basics.

Congratulations!

You have subscribed for Boating Basics Newsletter

You have subscribed for our SEO Tips & Tricks

A-Cat based trimaran from Lunada Design

29 July 2014     Editor    3 Comments.

GALLERY | Click images to enlarge

Long time Proa File contributor Chris Ostlind is working up a new ultra-light, hybrid human/wind powered tri based on an A-Class cat hull. Now that’s what we call recycling. Chris says:

I’ve been pretty much out of the design arena for a little over two years now, so I was excited when I was asked to develop a set of amas for a fast hybrid function boat being built by my friend and multihull guru, Mike Leneman. Mike’s boat is based on a hull from an A-Class catamaran, making use of a Hobie Mirage drive, as well as a snappy sailing rig for propulsion and the whole idea of a super skinny, and quick main hull pretty much lit my slumbering creativity.

The new boat features a modular aka/ama modular unit with mounting technology directly from the high performance Seacart 30 racing trimaran:

The aka beam ends are tapered, four sided conical shapes with matching receiver sockets in the vaka hull to accept the aka ends when being assembled. This set of shapes prevents any binding of the akas in their pockets and ensures that they will slide home firmly. The assembly is then kept in place with discreet water stays, which not only hold the thing together, but they redirect the loadings away from tensioned beams to forms that are now in compression… allowing for lighter fabrication and an overall lighter boat. Another design approach in use for this boat are the strongly shaped asymmetric amas. We haven’t tested this solution in the water yet, but we anticipate that the wetted shapes will provide enough leeway prevention to preclude the use of a keel appendage.

The great news is that even if you don’t have a spare A-cat hull lying around, Chris has developed a plywood/epoxy home builder version of the boat. Follow the development here on facebook .

From Chris Ostlind | Lunada Design

  New Designs   Trimarans   Smallcraft

Make a Comment

Thanks, Michael, for publishing the brief material on the new boat design. I’d like to emphasize that Mike Leneman originally developed the idea to use the A-Cat hull for this prototype project and that I was asked to create a lightweight design solution for the amas. After things were rolling along, Mike suggested that we create a complete boat for the homebuilders who might be interested in crafting one of these bad boys for themselves. With A-Class cat hulls hard to find on the used boat market, I drew a new hull that could easily be built and would function in the same capacity. The modularity aspect came from my desire to extend sailiong and boating through the use of a component solution so that small craft owners could really spread their boat bucks a long way. The successful XCR sailing canoe design makes use of the same philosophical design idiom and it has proven itself as extremely functional for coastal exploration.

Thanks for clarifying, Chris.

Hi Chris, I’ve always enjoyed and learnt much from your work. Future facing, innovative and beautiful.I’m really glad you’re back in the playground.Thanks for sharing your visions once again. Cheers for now, claudio

E-Books by Russell Brown

Russell Brown's boat building series will soon become your favorite shop tool

Featured Articles

• Proa Rig Options: the Biplane
• Proa Rig Options: Overview
• Proa Rig Options: Crab Claw
• Proa Rig Options: Gibbons Rig
• Proa Rig Options: The Sloop
• Proa Rig Options: Bolger Rig
• The Proafile Primer

Recent Comments

I am very interested in this type of boat for cruising the…

i want to talk to this guy mike port townsend wa. .(JavaScript…

• 03 Jul:   This article is 6 years old and that Craigslist ad is long gone.…   Editor

Nice looking boa Skip! Thanks for the story

Good to see that you are on the water and getting some…

• 16 Jul:   Alas, the bottom in that area of the Laguna Madre/Land Cut is…   Skip

I’ve been watching this new development with interest, Skip! …

• 27 Jul:   It may well be Spring before any video appears, I'm slowing…   Skip

Is there now a set of building plans available for Evergreen?

That is a very ambitious project! Is ther any further news?

Warren seaman was one of the finest individuals I have ever met.

Can you not turn the sculling oar upside down and use it as a

Can you not use the sculling oar as a barge pole in the…

• 20 Aug:   Yes the scull stuck in the mud to the extent that extracting it…   Skip

Do you have news for us?

If what you're doing is like the things you read about here - please write and tell us what you're up to. We're easy to reach right here .

Sites of Interest

• John Welsford Small Craft Design
• Trimaran Projects and Multihull News
• WoodenBoat Forum
• Traditional Small Craft Association
• Skinboat School
• Fijian Proa Documentary
• Proa Web Sites
• Watertribe - Everglades Challenge
• PT Watercraft
• Malibu Outrigger Manual
• Balogh Sail Designs
• Crab Claw Catamaran
• McGowan Marine Design
• Mehrrumpfboote
• Cheap Pages
• Cape Falcon Kayak
• Pacific Islanders Cultural Association
• Peter Worsley’s Wing Sails
• R2AK - Race to Alaska
• Angus Rowboats
• Nigel Irens Design
• Wakataitea Tiki 46
• James Wharram Catamarans
• Star Rigging

Log in or Sign up

You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser .

Cross beams/aka's for a 6m (20ft) trimaran

Discussion in ' Multihulls ' started by Aaron_de , Jun 6, 2016 .

Aaron_de Junior Member

G'day all, I'm building a self designed 6m /20ft lightweight demountable trimaran that separates into 3 sections; 2.4m bow section, 2.4m midships section + 1.2m aft section. Why you ask? I have a steep driveway that rules out a trailer but car-topping the boat is just doable. I have a ute (that's a pickup for you yanks!) which can hold the main hull sections while the rest of the boat, Mk3 Boyer A class cat hulls for ama's, mast and cross beams, is on the roof racks. My 3 questions for the collective wisdom of the forum are... 1. If I were to use unstayed aluminium tube section as the aka's what outside diametre and wall thickness would be appropriate? 2. Same question as above but for carbon fibre tube...? (Ha!Like I can afford it!) 3. What are my alternatives to aluminium/carbon fibre to keep them light but strong? Specifications of the boat for reference... - A class cat 4mm plywood hulls for ama's. Estimated weight is 15-20kg / 33lb-44lbs (I have not weight them as yet, anyone know the weight of these?) - 6.8m 22ft stayed aluminium mast. - would like to have at least 2 people on the tramps at any given time. - estimated mainsail area will be 12sqm / 130sq foot - jib 3.7 sqm / 40sq foot - screecher ? not sure but tack will be mounted on a 600mm prodder - main hull is 6mm ply, EPS foam and fibreglass/epoxy. - estimated main hull weight 100kg / 220lbs. - main hull draft at midships 600mm / 2ft - main hull beam at widest point 603mm - sailing beam 5.5m / 18ft - distance between aka mounts on ama is 2250mm / 7.4ft Thanks. p.s. It's my first post so be nice!  

tamas Junior Member

Hi Aaron, I have similar size boat but 4.8m wide when open and a lot more sail area. I used 100mm ally x 3mm wall thickness, it seems very sturdy but I am no expert. The folding system I have is similar to Farriers so it may offer some support to prevent tubes bending under load.  

patzefran patzefran

I have just launched my new built Strike 20 Tri. It is 5.10 beam . 5.50 m is very wide beam but you have very low buoyancy outriggers. Mine' are Nacra 5.80 hulls. I use 100 mm OD , 3 mm thick aluminium tubes and water stays. With such a wide beam you need waterstays. On my boat I have estimated waterstays max load was around 3000 daN on main beam. Best wishes Patrick https://www.dropbox.com/sh/wi2pj01emza07lv/AADocN3LlA25DjzdTHe0uM4Ya?dl=0 https://www.dropbox.com/sh/ug32rkrarsn83cy/AACE0uUOSLksidTXjNGY8VURa?dl=0  

tamas said: ↑ Hi Aaron, I have similar size boat but 4.8m wide when open and a lot more sail area. I used 100mm ally x 3mm wall thickness, it seems very sturdy but I am no expert. The folding system I have is similar to Farriers so it may offer some support to prevent tubes bending under load. Click to expand...

patzefran said: ↑ I have just launched my new built Strike 20 Tri. It is 5.10 beam . 5.50 m is very wide beam but you have very low buoyancy outriggers. Mine' are Nacra 5.80 hulls. I use 100 mm OD , 3 mm thick aluminium tubes and water stays. With such a wide beam you need waterstays. On my boat I have estimated waterstays max load was around 3000 daN on main beam. Best wishes Patrick https://www.dropbox.com/sh/wi2pj01emza07lv/AADocN3LlA25DjzdTHe0uM4Ya?dl=0 https://www.dropbox.com/sh/ug32rkrarsn83cy/AACE0uUOSLksidTXjNGY8VURa?dl=0 Click to expand...

Further to my initial question here's a rendering of my design which I'm calling the RUDI 6.0. In the graphic I'm comparing scale size of Hobie14 and Hobie16 masts. [/IMG]  

For the waterstays I use last generation of Heated pre stretched dyneema. I use twin 5 mm for each waterstay which gives 8000 daN breaking strength. I have also used 6 mm Vectran on the aft beams. Vectran is stiffer but has a lower breaking strength. The attachments are 10 mm bent U bolts on the main hull and 12 mm carbon rod through the aluminium beam at the outrigger side. I need to use very high tension on these stays to keep the platform tight, as my boat is on a mooring exosed to wind, waves and tidal current. Building Strike 20 was a lot of work too ! If you hit your 100 kg target for the mainhull, congratulation. My Strike 20 is about 350 kg total weight. Nacra 5.8 hulls are very heavy, 61 kg each ! Cheers Patrick  

Woah! 68kg is definitely much heavier that my A class hulls. Keeping your Strike on a mooring means you get to take her out all the time. Dyneema was my first choice for stays if I needed them, probably use single 10mm diametre stays which will go forward and aft of the aka's to provide fore & aft tension as well as vertical. Do you get a lot of spray in the cockpit from your waterstays? And at what speed? Unlike your Strike 20 my RUDI 6.0 doesn't have a flared cockpit (part of how I can keep the weight down) so the trampolines will extend from the ama to the vaka. I expect anything above 6-8 knots wind I'll be getting wet!  

waynemarlow Senior Member

Aaron, you may want to look up the TC601 build thread on this forum and build site http://lwr600.co.uk/TC601/index.html where you may get lots of ideas on build and such. You may also want to read through the thread on small 20ft tri's where the use of an A Cat was widely discussed and some calculations submitted to justify the use of such low volume hulls. I'll be updating the website to include how we have dealt with the beams, they have been really really difficult to get an easy and widely accepted method of building them without having weird looking attachment points to the donor hulls, that is widely available through the world. Sorry no the Farrier method is just too cumbersome and time consuming for the home builder, look more at the SeaCart 26 for inspiration.  

Thanks Wayne, do you know the name / have a link for the thread discussing A Class cat hulls?  

I think the three threads about under 20ft Tris' have a lot of info ( and also a lot dross in amongst it ) but the main one with mention and figures for the A class was http://www.boatdesign.net/forums/multihulls/t20-new-development-class-39874.html  

Some more practical data on 20 ft Tris. Two months after launching and solving some problems on our Strike 20, we sailed yesterday in a decent wind. You will find video here broad reaching around 15 kt : https://www.dropbox.com/s/6uk10p6q6jx85qn/VIRB0082.MP4?dl=0 Top speed was 16 kt, with 14.8 mean speed over 500 m and 14.3 over a nautical mile. Patrick  

Hi Aaron, Here is a blog I did on the build. http://husky6.blogspot.com.au/ I have been sailing for a couple of years now. I have since added a bit bigger jib and fat head main taking sail area up to about 27M2 which seems to have turbo charged it. I think I am just under 300kg, boat weight. Cheers  

Hi Tamas, Your boat looks very nice, congratulation. What is the maximum beam ? I think my Strike 20 is around 350 kg, as the Nacra hulls are very heavy. You should be as fast as me (see my last post). Have you any recent GPS record ? Patrick  

• Advertisement:

Doug Lord Flight Ready

Aaron-here is a thread with many tri's 20' and under: http://www.boatdesign.net/forums/multihulls/small-trimarans-under-20-a-43650.html  

LVL Crossbeams

Arched Or Flat Crossbeams ?

foldable cross beams...

Nicol Tri - Alloy Lattice Crossbeams

Small cat crossbeam questions

Normon Cross Trimarans

Cross Beam thoughts for small Tri

Aluminum catamaran cross beam height

Hull flexing on 49' Norm Cross Tri

Building hull in cross sections

• No, create an account now.
• Yes, my password is:
• Forgot your password?

Boat Profile

Seaclipper 16

A folding trimaran for the home builder

From Issue   January 2017

I ’ve built more than a few boats for myself in the past 38 years, and in all that time I have never been tempted to build a multihull. Why go to all the work of building two hulls, let alone three, when I’ve never found any of my single-hulled boats lacking in any significant way? I started getting answers to that question as soon as I stepped aboard a Seaclipper 16 designed by John Marples of Searunner Multihulls and one of nine designs in the Seaclipper series of trimarans. The hull is constructed of 7 sheets of 1/4″ six-ply marine plywood, five sheets of 3/8″ nine-ply, and lumber in commonly available sizes. Fiberglass-and-epoxy sheathing is optional. The instructions are geared for novice builders; full-sized templates for the bulkheads are provided in the plans. Stringers connecting the bulkheads define the shapes of the plywood panels for the hulls. The 15′ 11″ vaka (center hull) has a flat bottom that will take to landing on the beach without digging in or causing the kind of wear you’d get with a sharp V hull. The amas (outrigger hulls)  have bottom panels set at an angle, deeper outboard than inboard. This configuration adds a fin-like element for increased lateral resistance for sailing in shallow water with the daggerboard pulled up. The angled ama bottoms also present an edge to the water, keeping the amas from slapping the waves when they’re close to the water’s surface; it’s a quieter ride. The amas’ bottoms are positioned higher than the vaka’s bottom, so their edges are not subjected to wear when the boat is hauled up on a beach.

Each of the four swing-arm akas has three bolts: one securing the pivoting part of the aka to the ama, and two (one of those anchoring the shroud bridle) connecting the pivoting part of the aka to the fixed central section on the vaka. Removing the inboard bolt allows the swing arm to pivot, moving the ama aft and inward.

The akas (crossbeams) can  be made in three ways: as one piece bolted to the three hulls, hinged to fold the amas on top of the vaka, or as swing-wings, like LIMONADA shown here. With the swing-wing, the amas pivot aft and nest against the vaka, bringing the beam down from 11′ 3″ to 7′ 7″ for trailering and to fit in a standard marina slip. The swing wings can function whether the boat is afloat or on a trailer, so they are handy when launching or landing at a crowded boat ramp. The swing wings don’t require any hardware beyond nuts and bolts, and have an advantage over the hinged akas: there’s no need to lift an ama and set it down gently on the vaka. The Seaclipper 16 can be built as an open-cockpit cruiser, or as a daysailer with a tandem cockpit, with the helmsman sitting in the aft position, legs straddling a centerboard trunk and the crew sitting forward. The 7′-long open cockpit has side decks between the akas that offer more options for seating, moving around while under sail, and sleeping aboard while moored.

John Marples, designer of the Seaclipper 16 and builder of LIMONADA, goes for a sail on the Mystic River.

L IMONADA, as an open-cockpit version of the 16, has a daggerboard deployed through a slot in the cockpit sole. A softwood stick wedged in the slot keeps the board down; it has a loop of line at its top for quick removal and raising of the board. The cockpit sole is high enough above the waterline that any water coming into the cockpit drains right out. The rudder is mounted on a false transom, hinged at the top, that allows the rudder to kick up when meeting an unexpected shoal or to be retracted when coming ashore. The downhaul at the bottom of the false transom leads to the cockpit for easy operation. The rudder blade is balanced and has enough of the blade ahead of the pintles and gudgeons to lighten the load on the skipper when coming about. It also allows the arms of the rudder yoke to be short and unobtrusive. The lines from the yoke lead forward to pedals in the cockpit to  for hands-free steering. A tiller above the yoke allows steering while sitting on a side deck and is the means of raising the rudder when coming ashore.

A hinged false transom allows the rudder to be kicked up. The tiller pulls the rudder up and holds it. The line at the bottom of the false transom holds the rudder down while the boat is underway.

The Seaclipper 16 is designed to take a Hobie 14 sailing rig. The pivoting aluminum mast, roller-furling jib, and fully battened mainsail are readily available from a wide network of Hobie dealers and may be found used in online classifieds. The Hobie 14 has a beam of 7′ 8″, so the Seaclipper 16, with a beam of 11′3″ can take better advantage of the 146-sq-ft sail rig without flying a hull to the brink of capsizing. Dyneema shrouds, secured to bridles spanning the side decks, support the mast. The plans include specifications for an unstayed wooden mast. For auxiliary power, a short crossbeam aft of the port aka serves as a mount for a small outboard.

The side decks provide seating when two are aboard, and the steering is then done with the tiller, not the foot pedals.

I had a chance to sail LIMONADA, the Seaclipper 16 built by Marples for Mac MacDevitt, on Mystic River near Mystic Seaport. Stepping aboard, I got my first lesson in the values of a multihull. I didn’t have to lunge for the centerline as I do with my monohulls to keep them on an even keel. The trimaran has plenty of stability no matter where I put my weight and the amas (outer hulls) have enough volume of to support my 220 lbs. Without having my movement aboard the boat restricted by the nagging demands of a monohull, I could wander around the boat. The decks are all flat, so the footing is good everywhere. While I like the sweep of a curved sheer line, the Seaclipper’s flat decks simplify the construction of the boat and provide the geometry required for the swing-wing akas.

The deck surrounding the cockpit is large enough to set up a tent for sleeping at anchor. The windshield was added by the builder to block spray when sailing into a brisk breeze.

I liked being able to walk around the boat while it was under sail with Mac at the helm. I never get to see my own boats moving through the water, so stretching out on an ama to watch the vaka’s bow at work was a treat. The 7′-square deck around the cockpit offers a place to pitch a tent. Mac has a two-person tent with an oval hole in its floor to match the cockpit opening. He can sleep to one side of the cockpit, sit comfortably upright with his feet in the cockpit and have access to the gear stowed there. The amas and vaka offer plenty of room for cruising and camping gear; commercial plastic hatches offer access.

I took LIMONADA out by myself and enjoyed steering with my feet and having my hands free to manage the sheets. Nestled down in the cockpit on a padded seat with a backrest, I was very comfortable and relaxed. The sheets were right in front and could be cleated off, making sail-handling a breeze; there was no need to switch sides or do-si-do with a tiller when coming about. During my outing the weather was warm and the wind was light, perhaps 8 to 10 knots at best with a few gusts, but in a cold wind, being mostly below deck level would be a boon. Mac had made a removable windshield that wraps around the forward end of the cockpit for even greater protection from cold wind and spray.

With Marples and owner Mac MacDevitt aboard, LIMONADA flies the windward ama. The leeward ama still has plenty of freeboard.

The light wind was more than enough to get Mac’s Seaclipper going at a brisk pace and fly the weather ama. There was no spray, so I stayed dry, and even with the boat moving at a good clip I didn’t notice any water coming up through the daggerboard slot.

I was surprised by how well the Seaclipper could come about. With three hulls in the water, I thought there would be a lot of drag in the turns and that the boat would get bogged down, but the rudder blade and the centerboard have enough area to swing the bow around before the boat loses momentum. I never got caught in irons, but I backed the jib for a moment to hasten the bow’s falling off and the filling of the main.

LIMONADA owner Mac MacDevitt reports that his Seaclipper 16 is “super fun in a stiff breeze.” Here, sailing with a reefed main on Lake Champlain, he estimated his speed at about 13 knots. “It was exciting, but I felt safe and secure.”

Christopher Cunningham is the editor of Small Boats Monthly.

Seaclipper 16 Particulars

Length/15′ 11″

Beam/11′ 3″

Beam, amas retracted/7′ 7″

Draft, hull only/11″

Draft, board down/2′ 7″

Sail area/127 sq ft

Displacement, dry/400 lbs

Displacement, full load/800 lbs

Plans for the Seaclipper 16 are available from Searunner Multihulls for $180.

Is there a boat you’d like to know more about? Have you built one that you think other Small Boats Monthly readers would enjoy? Please email us!

Share this article

Join The Conversation

We welcome your comments about this article. If you’d like to include a photo or a video with your comment, please email the file or link.

Comments (2)

Thanks for the multi-hull perspective. Lots of cool ideas.

I’ve been looking. This could be the one!

Comments are closed.

Stay On Course

More From This Issue

From The Editor

Roller Carts

Like Ben Fuller, I have more boats than trailers to haul them, so when I read his article on the roller cart he built with Joe Liener, I was convinced...

I already had a sailing dinghy and a sail-and-oar skiff in our two-car garage, but I thought there was room for one more boat, a small one, alongside my wife’s…

I’ve built more than a few boats for myself in the past 38 years, and in all that time I have never been tempted to build a multihull. Why go to…

A Lakeland Row

A couple of years ago I spotted a long, lean traditional Finnish rowing boat for sale online. It had been designed and built for bi-stroke racing with a rower on a…

Joe’s Roller Cart

Decades ago, my friend Joe Liener introduced me to duckers and melonseeds at his little boathouse in Wittman, Maryland, on the eastern shore of Chesapeake Bay. Joe had retired some…

If I can keep my head, feet and hands warm while I’m rowing in cold weather, the rest of me stays warm; pogies are my winter hand covering of choice.…

Product Reviews

Thin Rip Table Saw Jig

If I had my druthers, I’d make knees, breasthooks, and stems—all those angle-reinforcing structural parts of boats—out of grown crooks, but they’re hard to come by and take time to…

Reader Built Boats

John Adamson visited the WoodenBoat campus in the fall of 2009 and was taken by two Jericho Bay Lobster Skiffs: the original plank-on-frame version built by Jimmy Steele in the…

More Boat Profile

Like many of Welsford’s small-boat designs, the Sei combines a relatively narrow and flat bottom panel with three strakes of glued lapstrake planks over 1/4″-plywood frames. The hull is built…

The Meaban is a development of the Stir-Ven, which is slightly smaller but has a larger cockpit, a small cuddy instead of a cabin, and a transom-mounted outboard instead of…

The MerryMac

The MerryMac catboat tends to make the blood hum with a sense of adventure and challenge. Its owners claim that it has always been so since the first of about…

AdvancedFrame Sport Kayak

I kept coming back to the sweetly designed 10′ 6″ AdvancedFrame Sport Special Edition from Advanced Elements. With its semi-enclosed cockpit, moderate 32″ beam, and enthusiastic reviews, it seemed a…

Subscribe Today!

Become a subscriber today and you’ll recieve a new issue every month plus unlimited access to our full archive of backlogged issues.

Already a subscriber?   Sign In

Subscribe For Full Access

Flipbooks are available to paid subscribers only. Subscribe now or log in for access.

Lunada Design

Creative Boats for Home Builders

Category archives: demountable trimarans, back bay sit on top kayak, a modular system approach to sot kayak sailing, paddling  and mirage drive propulsion.

Sit-On-Top (SOT) kayaks are easy boats on which to learn to paddle. They have none of the “get in the coffin and you are about to drown” psychological identity that one finds in the Sit-Inside boats and they’re amazingly adaptable to a wide range of paddling activities. It also doesn’t hurt that they are pretty straightforward boats to rotomold, which makes them very cheap to produce in large numbers.

I didn’t envision just one boat for this niche in the home-built kayak market. Instead, it came to me that there would need to be at least three models that could address the wide-ranging styles of boating interests in this area of the kayak world. The result was a couple of very clean, SOT models at 14’ and 16’ called the Corona and the Back Bay, respectively. The third model was going to be called the Wahoo, as it was specifically designed for the folks who spend a lot of time fishing with their SOT’s. I’ll get to the Wahoo in the next article.

As a canoe and kayak sailor and a guy who had just been out for a test drive on the Hobie Adventure Island, which is based on their 16’ SOT Adventure model, I wanted to offer my own take on what makes for a truly fun and stylish, sailing SOT kayak. The result was that a fully integrated system of component parts was designed for the basic Back Bay. This modular approach allows the Back Bay to go sailing by simply adding a system of light-weight, easily built elements that quickly convert the SOT to a single aka sailing boat called the Scorpion, OR, to a double aka sailing boat with slightly larger ama volume, called the Doubloon. Of the two configurations, the Doubloon is most like the well-known and highly respected, Hobie Adventure Island.

The Corona and the Back Bay are virtually identical models, save for their respective lengths. For the purposes of this article, I’ll focus on the Back Bay version and all the potential add-on systems I’ve incorporated in the design.

THE BACK BAY SOT KAYAK

Specifications: Length overall – 16′ Beam overall main hull – 28″ Depth of hull max – 12” Weight – 48 lbs. or less Displacement – 335 lbs.

This boat is built in the S&G style of construction in 4mm marine ply with 6 oz. plain weave fiberglass set in epoxy on the inside and outside of the hull for full laminate sandwich strength. The build process uses external cradles as building supports, ensuring that the hull goes together with minimum hassle when handling the rather slender and longish hull panels. The boat is bulkheaded internally at three key points. These bulkheads create not only integrated strength in the design, but they also cleanly separate the hull cavity into four unique volumes for gear storage and watertight flotation.

The Back Bay can be configured with a large, open tankwell set aft of the cockpit, or built with a watertight, aft hatch cover for internal storage in a conventional kayak style.

Specifications: Beam overall – 10′ Weight (est.) – 90 lbs. Sail Area – 56 sq. ft. Displacement – 350 lbs. Draft (board down) – 28″

The Scorpion variant is a Sit-On-Top design for fun sailing, paddling, or Mirage peddling… or all three, as the builder desires. There will be a design for a leeboard mount included in the plans for those who are going to build the boat for sailing. Having the aka gull wing form set well forward permits a full paddle swing arc.  The aka beam connectives to the amas is split into a pair of mounting elements. I did this to make for a stronger, single beam mounting struture. With a single beam design, there is a tendency for the am to want to rotate around the beam, making for a very stressed component that could lead to early failure. By splitting the beam and spreading the mounting points, I have given the structure more resistance to this rotational force, making for a more rigid boat in use. This setup will allow the owner to power sail in light air with both the paddle and the sail providing thrust. With the leeboard swung down for sailing, the owner can do some “power sailing” and utilize the Mirage drive, as well as the sail, in light conditions. The Mirage is capable of boosting boat speed enough that it creates apparent wind over the sail, adding power where there really isn’t enough for sailing alone.

The amas are positioned to optimize capsize resistance when sailing off the wind. The amas do not touch the surface of the water at rest in stable trim and provide only minimal wetted surface drag when underway by paddle or peddle. As soon as the sail is loaded by the breeze, though, the ama on the lee side begins to immerse, firming-up the boat and resisting the heeling moments being generated.

The aft deck can be configured as a watertight hatch with full access to the aft sections of the hull, OR a large, diving tank well with self-draining ports. The cockpit is fitted with self-drain ports under the seat as well as forward, in addition to the daggerboard slot. There is a watertight deck plate just forward of the seat, between the knees of the sailor/paddler to provide secure storage for critical items that may be needed on a routine basis. The foredeck has a watertight hatch cover for bow storage needs.

The rig is a fully battened Dacron sail with two reef points and a multi-section, self-supporting mast which steps into a sealed mast socket in the hull. The mast and boom sections can be aluminum or carbon, as budget permits. The sail choice is open for the customer as long as it can be balanced with the fixed positions for the mast and dagger board. The Cunningham is run to the deck of the gull wing aka to keep the rig on the boat in the event of a capsize.

With 56-sq. ft. of sail on a 90-pound boat, this will be a decently speedy boat without being in over its head all the time in a stiff breeze. I suggest two reef points in the sail to allow for sailing in a wide variety of conditions.

This will be a wet boat at speed, yet there are no worries at all for flooding and sinking, save for a truly nasty trip over a reef that shreds the entire underside of the craft. The bow, cockpit and aft hull volumes are all independent, sealed compartments, as are the ama volumes.

Reentry from a swimming session will be easy with a simple, sling, or rope ladder much like those used by rock climbers, called etriers.

The boat is constructed in a multichine, marine plywood style with epoxy glass laminates inside and out in a stitch and glue style. Stainless T-Nuts are embedded in the hull deck surface from below to provide a secure set of mounting points for the aka wing. The amas are held in place on the aka tips by large bungees and a notched lock system. This system provides for quick setups on the beach.

You just fit the aka to the foredeck, insert four, 1/4″ threaded stainless screws with comfortable, knobbed grips and screw down the aka wing. The amas slip onto the ends of the aka and you lift the pair of 3/8″ bungees up and over two raised hooks on the aka ends to secure the ama in place. Simple, easily maintained and near foolproof in operation.

DOUBLOON SAILING SOT

The Doubloon is the second variation on the central SOT theme of this group of boats. In this design, I am looking to provide a more expansive utility application for the base, Back Bay SOT version. The Doubloon is essentially a solo craft and it carries the same, 56 sq. ft. sail, but the overall potential of the boat is expanded through the use of dual akas and full trampolines on both sides of the Back Bay hull. The rendering of the Doubloon shows a daggerboard inserted down through the Mirage Drive trunk, but in use, I would prefer to have the board mounted outside the Back Bay hull as a leeboard. Plans will be supplied with the leeboard solution.

The akas on the Doubloon are spaced to allow for a full paddle stroke with the boat setup as a trimaran. There are two sections of tubing that span the opening fore and aft between the akas from which the tramp is mounted. The trampolines are designed to roll-up on the outer tube section, much like a window shade and they are deployed by an endless loop of light halyard line. With the tramps fully deployed, the inner tube section lifts up and over a holding pin in the aka and the sailor applies as much tension to the tramp as he feels he needs by hauling-in the endless loop line and cleating it off. If a paddling session is desired, he simply pops the jam cleat and pulls the line to roll-up the tramp on the outer tube section. This procedure applies for both port and starboard tramps.

Like the Scorpion, the Doubloon can be built to utilize a Mirage drive in the center well and the need to roll-up the tramps for paddling is essentially negated, (though it is nice to have the option once in awhile as Mirage drives can be difficult to maneuver in tight places)

The aka beams are held to the deck of the Back Bay hull with the same, threaded knob strategy for quick setup and takedown times. Similarly, the amas are held to the aka ends with hefty bungee cords for the simplicity of use. There’s another, rather invisible, benefit to using the bungee cords for ama mounting. Because they are being held in place through a fairly dynamic hold-down system, the amas can move about, ever so slightly, while underway. This allows the amas to have some structural “give” and the result is that the banging and thrashing that is typically experienced by the ama, is somewhat dissipated through the flex of the joining system.

All in all, I think the Back Bay SOT should be a really fun boat to own for warm water/warm weather boating adventures. It has the capacity to carry enough gear for several days out on the water. When rigged with a sailing system of your choice, it can also cover some pretty good distances if the winds are favorable. Plans for this boat and all its variations will be available from this site and Duckworks Magazine.

Chris Ostlind

Lunada Design Chris@Wedgesail.com

Solo 12 and 14.

CORSICA 15R

Sports car performance on the water.

Over the past couple of years, I have taken a break from my boat design work. During that time, I’ve been able to reassess my connection to the craft. The last boat I designed was the Europa 20, which is a trimaran meant for vertical strip foam construction with sandwich style, infused epoxy/glass laminates inside and out. The Europa is a boat for very fast day sailing with a very light hull and a very big rig. A boat that is not for everyone, to be sure, as it requires a level of skill that the average guy does not typically cultivate in the course of experiencing their recreational boating interests.

In stepping away from the larger, more powerful beach type multihulls, I came around to the desire to produce a smaller, very quick and sensitive boat that would appeal to recreational sailors and not just those guys who want to blast around with their hair on fire (though I do suspect that in the right hands, this boat will do just that). The new design had to be easy to build with standard, marine plywood/epoxy/glass techniques that did not rely on exotic layups with spendy carbon cloth. (Well, maybe the carbon will sneak in there a bit on the beams for the guys who want to play with a bigger rig)

Looking long and hard at the smaller skiff-like hull designs I had done before, such as the Montage, I decided to draw the new boat in that same general size, but with a very different approach when it comes to how the boat achieves its performance potential. Where the Montage has a relatively spacious cockpit capable of taking on a couple of adults, (or a parent and a couple of smaller kids) the new, Corsica 15R trimaran would be for one adult (or accomplished kid) designed solely for a unique, one-up sailing experience within the small beach multihull genre.

As a result, the boat has minimized clutter when it comes to excessive high-tech trickery. With that approach, the Corsica 15R is also going to be a boat that has much lower maintenance requirements in order to keep it in top sailing condition, as well as a much lower realized cost to get it on the water and ready to sail.

If you are into cars, as I am, then think in terms of a nicely pumped, Mazda Miata, type of boat that would be a cool, weekend canyon racer for one person. A boat that could blast around the local waters in a good breeze and give chase to other small, fast, multihulls being sailed by crews of two.

The result of this conceptualizing process is the Corsica 15R. The C15R is a boat of modest, marine plywood build techniques and is very light weight for its generous sail area. With this boat, the normal sailing position would be the skipper, semi-reclined within the main hull, driving his machine like an F1 Grand Prix car. In this configuration, the boat is designed to utilize foot pedals for steering, leaving the hands free to work the sheets. But, that’s not the only way to sail this boat. Owners who wish to sail in a more conventional multihull style, can sit-up out of the cockpit and onto the main hull cockpit gunnel, or even the trampoline surfaces all the way out to the ama, where they will steer with a tiller extension.

A construction style in multichine, 4 mm marine plywood, allows the boat to be assembled in a well-understood fashion that will go together quickly. With a subtle placement of minimal stringers and sufficient bulkheads, the C15R becomes a strong main hull shell that can absorb the loads from its sizeable rig, turning the power of the sails into forward thrust in the water.

There is no fully enclosed transom on the vaka hull. The cockpit deck is slanted gently down and aft for automatic self-draining, such as is seen in sport dinghies and larger race boats. A collection of bulkheads under the cockpit deck provide structural support and watertight compartments ensuring that the boat will not likely sink even if large sections of the bottom are torn out from an underwater hazard while smoking along in a gin clear lagoon.

The demounted boat can be assembled easily by one person. The gently gull-winged akas are built with a glassed box beam core.  The inboard ends of the akas slide into tapered sockets in the main hull and are levered in place with stainless waterstays to make ready for sailing. This, tapered socket technique prevents binding while assembling the boat, while providing a solid, hassle-free and weight minimized demounting system. The leading edges of the akas are smoothly shaped foam blocks that are glassed onto the box beam to provide an aero component, as well as creating reduced drag from waves and spray. The akas are hard fastened to the amas as a complete assembly that is easily removable from the vaka hull. The trampolines stay mounted to the akas and amas for transport and only have to be hooked and tensioned to the main hull during assembly.

The mast is a stick from a Hobie 16. I specify the addition of a set of spreaders from the Hobie 18 mast to stiffen up the H16 mast to handle the additional righting moment generated by the Corsica design. Naturally, I’d prefer to see fresh sails in something like fully battened, Pentex laminate, but builders on a tight budget could also work with a loft service to tweak a reasonably fresh Hobie 16 main and jib and do just fine. The addition of reefing points on the main are strongly suggested, as well as the use of furlers for the jib and spinnaker/screacher. For those who desire fresh sails for this boat, I would recommend the folks at Whirlwind sails in San Diego, California. http://www.whirlwindsails.com/

A removable carbon prodder sets the tone at the front end of the boat. The stick originates as a carbon windsurf mast, so it is easily found on the used market and equally replaceable, should it get poked into an unyielding environment. For trailering, the sprit unpins, slides out of its socket and is stowed in the cockpit for transport and storage.

Corsica 15R Specifcations

LOA                                         14’ 11”  (4.54 m)

BOA                                         13’  (3.96 m)

Displacement                         650 lbs.  (294.8 kg.)

Sail Area (upwind)                 218 sq. ft.  (16.17 sq. m)

Spin                                       142 sq. ft.  (13.19 sq. m)

Mast Length                           26’  (7.62 m)

Draft (board up)                     1’  (.3 m)

Draft (board down)                42” (1.07 m)

The mast is raised by the traditional beach cat method of physically lifting the mast with the base pinned to the mast step, or by utilizing the long daggerboard in its trunk as a form of a gin pole. A forward hoisting line is led over a pair of sheaves at the top of the daggerboard and down to the hand cranked winch on the trailer. Mechanical leverage quickly raises the mast so that the forestay can be fastened to the bow, stepping the mast securely. You can see a few photos of the process at Brent’s L7 trimaran site:

http://home.comcast.net/~ritakend/site/?/page/Mast_Raising/&PHPSESSID=864f3404e3f46ed29dd99b863018fc1d   This is a very simple way to raise a mast should you need to avoid the trad lifting exercise for one reason or another.

I chose to not go with tricked-out, curved lifting foils in the amas due to construction complexity and added cost for the builder. Foils of this type are hard to build correctly by hand, as are the needed curved trunks in which they slide. Instead, the boat is equipped with a daggerboard that is inserted through the deck of the main hull in front of the mast which angles aft to exit the hull below the waterline. A daggerboard and trunk of this type are much simpler forms to build and orient in the hull. It is also just one main foil, where lifting foils need to be made in pairs, one for each ama. Lifting foils also need complex control mechanisms to retract and deploy the foils and they have to work from the cockpit remotely with the foils mounted way out in the amas. The needed controls are an interesting problem when the boat is 13’ in width and the driver is semi-reclined in the main hull.

Note: I’m not against an owner who might want to experiment with foiling for this boat, even if it is just foil assist and not full flying. It would require a lifting t-foil style rudder and twin Bruce style foils in the amas, or, if a person is really accomplished as a composites builder, they could make a pair of matching c-foils for the ama. The owner just needs to know what level of additional work is involved and at what skill level they need to perform in order to get the desired result.

If you are on a budget, the rudder and headstock from a Hobie 16 will work just fine for the Corsica with some mods to the tiller. The more deluxe, Rudder 25 system from Dotan will also work well, should you have the coin.  http://www.dotan.com/  If you plan on pushing the boat hard, then a longer blade will be required, or you can get yourself invested in the process of putting a rudder on each ama and have stunning control at your finger tips. On the down side, that change will cost you a bit out of your pocket and at the launch ramp in setup time… though I can see a nifty rig with light alu tubing and the use of snap buttons as a cool solution.

The Corsica 15R will be a light boat built from familiar materials. It should be a fairly simple building experience for the owner and will fit comfortably into any typical garage space, making it easy to find a building location. It will quickly assemble for sailing and be hassle free with minimal maintenance required to keep it in top form. It can be towed behind any compact car on a typical beach cat trailer and when demounted for travel, is road legal anywhere in the world. On the water, this boat should be quite quick and behave with predictable, pin-point sailing manners. With the skipper slung comfortably in his reclined cockpit seat, he will be decently protected from the effects of the weather and sea state while tearing around his local waters.

NAGARE 21′ AND 17′ MIRAGE DRIVE SPEEDSTERS

Making use of mirage drive propulsion with more efficient hulls designs.

Nagare  (nah-ga-ray) is a Japanese word meaning Flow.

Both of them are configured as trimarans with fairly small and unobtrusive amas designed to give the boats remarkable stability in a wide range of conditions while allowing the vaka, (main) hull to be decidely slender for more effective drive through the water.

The Nagare sisters also have incredibly narrow waterline beam numbers that, when coupled with their fairly long hulls provide for very easily driven hull forms for high efficiency per unit of energy applied.

I expect both boats to operate at the very high end of commercially available paddled boats of the same length, beam and weight. So, yes, they can go pretty quickly, but that’s not the real purpose.

The real benefit of the design genre is through the ease with which they are propelled at any given speed, compared to other boats of their size. This efficiency translates directly to those using the boats as less tiring for miles covered, or greater speed with the same effort as other, wider designs.

Because the propulsion is derived from the largest muscles in your body, the leg muscles, rather than the arms and shoulders, there will be less fatigue for each mile traveled. Because leg muscles are so much bigger than arms, they will be able to do more work in a given period of time, making for longer possible trips, as well as the mentioned lower fatigue issue. With a less fatiguing effort, more people will be able to enjoy the experience of being out on the water for daylong adventures.

NAGARE 21 DOUBLE SPEED AND STABILITY FOR DOUBLE RECREATIONAL BOATERS

The Nagare 21 uses a set of amas, mounted on a pair of simple, anodized aluminum tubes with quick release snap buttons holding the sections together for easy disassembly for car-topping. If a trailer is used to transport the boat, the beam of the Nagare 21 falls well below trailer maximums, so nothing special needs to be done to take the boat to and from the water. Two Nagare 21’s can be trailered, or car-topped, by removing one of the amas and placing the main hulls close to one another on the racks, or trailer. The removed amas easily fit inside the hulls and they are ready to go. The whole affair on the rooftop is very much like a pair of sea kayak doubles. Because of the length, I would not mount a boat this big on any compact cars. You would be very likely to rip the rack right off the roof in strong side winds.

Steering is by means of a simple, flip-up style kayak rudder with control lines run through the hull to a convenient steering lever in the cockpit. I suggest the SeaLine SmartTrak rudder system (do a search for supplier), the P-41 Multi-purpose rudder from Onno Paddles http://www.onnopaddles.com/onnocomponents.html and the Feathercraft rudder system for hardshell boats. http://www.feathercraft.com/accessories/rudders-hardshell.php   These are really great rudder units and will give excellent steering control with minimum drag.

NAGARE 21 SOT OPTION

This boat can be built with a full cockpit tub so that it functions as a Sit-On-Top kayak with full drainage through the Mirage drive openings. Auxiliary drain ports are located in the tub for rapid removal of any water that comes in over the side of the hull. I suggest the SOT option for warm water users, with the more traditional kayak style, Sit-Inside hull form for those who will be using the boat in colder water, or more frequent inclement weather.

The SOT version has internal bulkheads for support of the SOT tub, along with the capability of adding a small circular deck plate for an additional watertight compartment in the cockpit that is perfect for small items, such as cameras, wallets, car keys, etc.

The SOT variation is an optional element to the base plans. If you wish to built it as an SOT, drop me an email at my regular email address and I’ll get back to you.

ROUGH WATER USE

This is not really a boat that is meant to go out in rougher conditions, such as those where a full-blown sea kayak might be right at home. It’s meant for quieter waters, such as lakes, bays, harbors and bigger rivers. It can take a session in 1 or 2 foot breaking surf, but I would not expose the boat to bigger waves, especially in a shore break scenario. You may find yourself out from the shore a bit when the wind comes up, producing steep, choppy waves. The basic Nagare 21 will handle this easily because only the cockpit will be exposed to swamping. The amas will keep the boat stable while you pedal to shore, or a quieter place on the water, where you can bail-out the boat and continue.

It is a perfect boat for sightseeing, bird watching, fishing, photography, and just simple, energy efficient cruising with near bomb-proof stability (you can stand up in the boat while out on the water without your partner coming completely unglued, for instance).

The Nagare 21 is a fast, comfortable and unique boat for a couple who like to get out on the water, but do not want to hassle with the business of capsize that is present in other types of boats, such as kayaks and even canoes.

NAGARE 17 SINGLE A NEW STYLE OF SOLO BOAT FOR TROLLING FISHERMEN

The solo version of the Nagare series has some very different twists, compared to its bigger sister. It has the same, highly efficient and easily driven, slender hull technology, the same set of trimaran style amas well aft for big time stability, the same generous cockpit opening and the same convenient utility for car-topping or lightweight trailering.

The design elements that set this particular boat apart from its sister craft is that the Nagare 17 has a very special capability when it comes to fishing.

AFT FACING TROLLING

Anybody who builds the Nagare 17 and intends to use it for fishing will probably be knocked-out by the potential for facing aft while trolling. Imagine using your legs to quietly drive the boat forward while you casually set trolling rigs, eat a sandwich and keep an eye on the fish finder… all while keeping an eye on the rigs you have set, with them easily at hand?

This is the signature utility development with the Nagare 17, designed specifically, for fishermen. It works like this…

The fisherman loads his boat, drops into the forward facing seat, hits the iPod for his favorite tunes and jams out across the lake at a remarkable speed for a human powered boat. He zips across the lake in virtual silence because he’s driving a very skinny and efficient hull with no engine sounds. Once he arrives, he’s going to make a few sneaky trolling passes with his Mirage drive pushing him along over that monster crew of Pike that are hanging around on their favorite piece of structure. Wham! Fish On! and the day starts with smile on his face.

If you’ve ever fished from a typical Sit-On-Top, you know that you have to face forward while trying to look over your shoulder while trolling. Hook-up and then you have to swivel around, grab the rod and go after the fish. All the time you are doing this, you have to balance the boat carefully, because the whole tamale could go over and end your day right then and there.

Well, that’s how you used to do it, anyway.

With the Nagare 17, you can take it to a whole new level of fishing pleasure. The Nagare 17 is equipped with twin Mirage drive trunks. When driving the boat forward and facing forward, the Mirage drive is dropped into the forward trunk and a tractor-style seat is dropped into the aft trunk with the seat bottom resting on the top of the trunk.

To convert the boat to aft facing trolling and fishing, you simply stand up in the boat and swap the Mirage drive for the aft mounted seat plug and the seat then goes to the front trunk… facing aft. With the Mirage drive still set to drive the boat forward, you simply sit down and start pedaling, slowly, up to your desired trolling speed.

Now, you can watch your fish finder, GPS and your trolling rigs while you continue to tool along at your favorite speed for nabbing the fish. Get one on and simply work that rod while continuing to face aft. No twisting around in your seat, no ”just about dumped it” scenarios, just simple, fun fishing in a very stable boat. What could be cooler than that?

With the fore/aft balance point of the boat set right between the two drive trunks, there is but a very minimal change to boat pitch when you change the direction you face.

The Nagare 17 is further designed to accept an insulated and watertight tank between the two aka tubes where they run through the aft deck. You can use this for all kinds of stuff like: your catch, fresh bait storage, cold beverages if you catch and release… whatever suits your needs. There is plenty of room between the two drive trunks for a pretty good sized tackle box and lots of room up forward of the trunks for any of that “other stuff” that fishermen seem to sneak aboard their boats.

A moveable electronics unit can be fastened at the forward end of the cockpit, or unhooked and moved around aft if you’d rather have it facing that way.

Maybe you want to cast lures or flies instead of troll. The boat is so stable with the two, wide set amas, that you can stand up and cast all day without ever feeling like you are getting the least bit tippy. All in all, the Nagare 17 is quite a boat for fishing, as well as just plain fun, recreational pursuits.

The Nagare sisters represent a unique design family for human powered vessels. They are quick, stable and with their unique styling, represent a distinct departure from the looks of traditional boats one typically sees on any given shore or launch ramp. Both boats are designed to be built in marine ply Stitch and Glue methods for the hull sections, with cedar stripped decks to take advantage of the really beautiful, smooth curves capable from that style of building. You can paint the lower sections of the hull and leave the cedar decks natural with a deep varnished finshed, for a real knock-out boat that will really gather a crowd.If you really want to have a plywood deck build instead of the cedar strip build, write and twist my arm gently. I can design that change for those who really like to build that way

Plans are not yet complete, so if you would like to build one of these two boats, please send me an email and I’ll put your name on the mailing list for information, or watch the plans section of Duckworks for the notice.

CHRIS OSTLIND LUNADA DESIGN CHRIS@WEDGESAIL.COM

Another Trimaran/Skiff … Bigger, With More Power

Well, you had to know this would happen…

When the Montage Skiff/Trimaran was introduced, the Lunada Design website was absolutely flooded with an ocean of page hits every day right after the article was posted. I received several dozen personal query letters regarding the boat and sizeable slice of them were directed at the potential of a bigger version of the Montage.

The concept of being able to build your own boat and rig it with a used mast and possibly even used sails, (if they are in good enough condition) had struck a chord with the homebuilding community. The creation of a larger version of the Montage would take the specified rig choices up into the much more commonly found beach cat rig sizes and make the business of finding a used rig in great shape, a whole lot easier. After pencilling a collection of thoughts and running some rough numbers on the potential, the idea came into focus as the 18′ Collage.

The ama shapes, especially on the smooth hulled variation, borrow other design cues from the modern performance dedicated French designs of VPLP, as well as the very cool work of Nigel Irens. The transoms are nudged in the direction of a triangular shape, while retaining some of the typical beach cat, flat-topped U-form feeling. The volume concentration is well-forward, with the foredecks being much more rounded to provide rapid shedding of water. These shapes will help to reduce the tendency of multihulls to pitchpole when sailed hard.

Breaking away to some degree, from the single, build style of the Montage offering, the Collage is presented as a fully strip built, smooth hulled version, as well as a multichine plywood version. These choices will give builders the ability to work with the material choices and aesthetics they prefer. I am also looking at the potential for a foam cored sandwich laminate boat using the vertical strip technique, though that iteration will probably come around a little later in the process.

Collage Specs

LOA 18′  ( 5.48 m ) BOA 14′  ( 4.26 m ) BOA main hull 41″ ( 1.04 m )

Sail Area Main 163 sq. ft. (15.14 sq, m.) Jib 55 sq. ft. ( 5.12 sq. m. ) Spinnaker 161.5 sq. ft. ( 15 sq. m. )

Displacement 1000 lbs. ( 454.5 kg. ) Weight 380 lbs. ( 172.7 kg. )

The Collage meets all the same design criteria as does the Montage, except it’s longer and wider, has more sail area, carries more crew weight and yes, it’s going to be faster in the right hands. Faster… sometimes this term can be kinda self-defeating when speed claims are made compared to another boat. When it comes to recreational boats, I’m of the opinion that speed is a relative thing based on the overall design brief of the boat in question. In the case of the Montage and Collage designs, speed is one of the attractive elements as long as it is kept in perspective with  just what the use application will be from day to day. From where I sit, this will be primarily recreational purposes.

The Sail Area to Displacement ratio ( SA/D ) for each of the boats is as follows: The Montage is 31.56 and the Collage is 34.88 With both of these boats being sailed at near max displacement, I give the nod to the Collage, based on waterline length, as well as the ability to punch through wave conditions that will toss the Montage around to some degree.

I would like to see this pair of boats ( Montage and Collage ) blasting around in the hands of skilled sailors. There’s nothing quite like the feel of a performance boat and the way it can deliver the exhilaration of a spirited ride. But… I’d also like to see this boat out on the water being used by families while they have a really fun day on the water with, maybe, a somewhat toned-down speed blast tossed into the mix every now and then to get the kids chirping.

I’m looking at the potential for the Collage to create a new beach and/or lake sailing culture in which energetic hot shoe dudes, as well as young sporting families, can all mingle on the beach, out on the water and share a communal BBQ after the day of sailing. I grew to maturity on the beaches of SoCal watching the brand new Hobie Fleets do this very thing and it was a lifestyle that perfectly fit my beach kid way of thinking. It would be great to see that happen once again. Could this take place in 2009? Hey, I don’t know the answer to that one, but it is fun to think of the boat and its owners in those terms.

There’s a lot going for the Montage/Collage design approach to support such a social event concept. Both boats are affordable to build, they are easily trailered by even sub-compact cars, they make use of “experienced” parts that can be had on the open market for pennies on the dollar when compared to new parts and they are boats that are easily sailed on the first day. This last part is important, as the boat will attract more enthusiasts when they see that they can be sailed with what pretty much passes for beginner’s skills. Just because it can go fast, does not mean it has to be sailed that way. As the owner’s skills grow, the boat’s potential will be there waiting for him.

As a way of introducing the Montage and the Collage designs to the homebuilder market, I’d like to offer free plans to one person. This builder should be able to show me that they have a very strong interest in either design and are willing to build the boat as I supply the plans in accordance with their progress from the previous plan set delivery.

If interested in this offer, you can write me at: Chris@Wedgesail.com or at lunadadesign@gmail.com and make your pitch. The one chosen to receive the free plans will be willing to provide construction photos of their progress and a brief written description as to how things are going. The personal accounts will be published on this website, Lunadadesign.net so that the readers of the site can follow the projects.

Chris Ostlind Lunada Design

This boat created immediate appeal to beginning and intermediate sailors. It offers much of the speed experience of a high performance skiff in a stable and predictable platform that is really tough to capsize. The Weta is one of the first boats to encourage family participation and reintroduces the waterborne fun of the beach sailing culture, established way back in the late 60’s with the intro of the Hobie catamaran.

A brand new, factory built Weta goes out the door for USD $11K. Realistically speaking, this isn’t an in surmountable amount of money for a factory produced, brand new carbon trimaran. It is, however, quite a lot of money for most casual recreational enthusiasts and the folks who like to build their own boats… especially when you consider the rugged economic conditions we all face these days.

The estimated $5600 figure represents a boat with a whole host of brand new parts. For the clever builders out there, the Montage could be even less expensive if they can find a used 470 rig, perhaps a used small craft, or beach cat trailer that could be modified to fit the hull design and even a collection of hardware in good condition. The Montage is a very light boat at right around 235 lbs., so you do not need to buy a heavy duty trailer.

I went back to the drawing table and reconfigured everything so that the longest hull panel was going to just fit on a couple of sheets of marine ply laid end to end. The main hull also got just a bit wider in the process of lengthening the boat. Where the factory boat uses carbon fiber on foam cores for its structure, the Montage will be a 4mm marine plywood design with full fiberglass/epoxy sandwich laminates inside and out. The foredeck and the cockpit seating transitions are strip-built in Red Cedar to give the overall appearance of the boat a smoother, more organic feel than straight plywood panels.

The amas for Montage came from a 16′ trimaran design that I had already done and required minimal re-design to work with this boat. The amas are also designed as multichine ply forms with pretty high volume shapes well forward and a water shedding deck form that will helps to keep them riding high even when driven hard. Ama displacement is 100% of the all-up boat weight when sailing.

Montage Specifications

LOA                                   15′ 6″ BOA                                   12′ BOA main hull                  41″

Main                               110 sq. ft. Jib                                      38 sq. ft. Screacher                      102 sq. ft.

Displacement                 650 lbs. Weight                             235 lbs.

The aka beams are anodized aluminum instead of carbon tubing. The inboard ends fit into fairly burly sockets in the hull and are held in place with quick release pins. Flat deck flanges on the ama ends are welded in place and bolted to the amas. The amas are removable from the aka tubes for repair or maintenance, but otherwise stay mounted, along with the trampolines, as complete units.

The mast is also anodized aluminum. The boat uses the same mast section as the 470 dinghy, which is a Proctor Cumulus section. This mast is available on the used market with a little bit of hunting around. If you want it all and have the money, then there’s a very cool, filament wound Forte carbon spar available with very close specs to the Proctor that will rock your world. http://fortecarbon.com/

Making these two changes from the benchmark, all-carbon Weta to an aluminum spar and tubing keep the costs down, with but a slight weight penalty over all-carbon parts. If you find a used mast, the savings will be even more substantial.

I have found that the more expensive sailcloth laminates are capable of driving the boat just a bit faster, but for the average recreational sailor, they will hardly ever make a difference compared to more forgiving sails in Dacron. Dacron is much easier to maintain, lasts longer, is a lot more tolerant of UV exposure and can be repaired by any sail loft wherever you go. If the builder of the Montage really wanted to, they could buy a set of sails in something like Pentex laminate instead and they’d have that hot, performance boat look that some desire along with just a bit more zip under sail.

The aluminum aka tubes will be sold pre-bent and ready to install on the amas. If the builder has access to a good mandrel bending facility that can handle the OD/ID specifications of the tubing, they can fabricate their own tubes to supplied specs.

The Montage is designed to be a really fun day sailing machine that can generate near performance skiff sailing speeds while offering a hugely stable platform for recreational sailing. Construction of the boat is very straightforward in marine plywood with glass/epoxy laminates and can be easily built by any sailing enthusiast who has household handyman skills with tools. The Montage has been created to offer homebuilders an opportunity to enjoy this style of family sport boat at a completed cost that is far less expensive than the manufactured version.

CHRIS OSTLIND

Fresh take on the solo16 s, a safe, speedy solo cruising craft for adventurous souls.

After a lot of input from readers of this site, I have completed the modifications to the Solo16 S design that reflect many of their expressed interests.

The Solo16 S now has a bit more displacement as a direct response to suggestions for the use of a small 2 hp outboard and some spare fuel. At the same time, the vaka hull was given additional beam above the waterline and the shear was raised some to allow for mods to the amas.

The amas, themselves, were made slimmer and taller, while retaining the same volume. They now have a slight vee section which gives the boat a progressive resistance increase as the amas are pressed heavily in a gust.

To complete the changes, a sporty all-weather soft cabin has been designed to allow the owner a chance to sail in a wide spectrum of conditions. The new cabin is modular in its approach with the ability to address a multitude of sailing situations.

All panels except the Bimini have generous window areas which are backed by micro mesh screen that is small enough to keep out the No-See-Ums. The PVC windows are zip-out removable and the screens can be rolled-up for maximum airflow through the cockpit. The complete enclosure system allows the owner to mix and match the panels as needed for the best protection from the elements.

When setting up the boat for sailing while on the trailer, the owner simply lifts the ama assembly, rotates and places the ends of the aka tubes into the matching vaka openings and slides the ama into place. The akas are fully seated when their internal, spring loaded snap-buttons click into place. The entire ama assembly is easily handled by one adult with modest physical strength.

In the trailering mode, the complete boat does not exceed 68″ (1.7 m) in width, falling well under every trailer width limit in the world.

• New Sailboats
• Sailboats 21-30ft
• Sailboats 31-35ft
• Sailboats 36-40ft
• Sailboats Over 40ft
• Sailboats Under 21feet
• used_sailboats
• Apps and Computer Programs
• Communications
• Fishfinders
• Handheld Electronics
• Plotters MFDS Rradar
• Wind, Speed & Depth Instruments
• Anchoring Mooring
• Running Rigging
• Sails Canvas
• Standing Rigging
• Diesel Engines
• Off Grid Energy
• Cleaning Waxing
• DIY Projects
• Repair, Tools & Materials
• Spare Parts
• Tools & Gadgets
• Cabin Comfort
• Ventilation
• Footwear Apparel
• Foul Weather Gear
• Mailport & PS Advisor
• Inside Practical Sailor Blog
• Activate My Web Access
• Reset Password
• Customer Service

• Free Newsletter

Ericson 41 Used Boat Review

Mason 33 Used Boat Review

Beneteau 311, Catalina 310 and Hunter 326 Used Boat Comparison

Maine Cat 41 Used Boat Review

Tips From A First “Sail” on the ICW

Tillerpilot Tips and Safety Cautions

Best Crimpers and Strippers for Fixing Marine Electrical Connectors

Thinking Through a Solar Power Installation

Getting the Most Out of Older Sails

How (Not) to Tie Your Boat to a Dock

Stopping Mainsheet Twist

Working with High-Tech Ropes

Fuel Lift Pump: Easy DIY Diesel Fuel System Diagnostic and Repair

Ensuring Safe Shorepower

Sinking? Check Your Stuffing Box

The Rain Catcher’s Guide

Boat Repairs for the Technically Illiterate

Boat Maintenance for the Technically Illiterate: Part 1

Whats the Best Way to Restore Clear Plastic Windows?

Mastering Precision Drilling: How to Use Drill Guides

Giving Bugs the Big Goodbye

Galley Gadgets for the Cruising Sailor

Those Extras you Don’t Need But Love to Have

UV Clothing: Is It Worth the Hype?

Preparing Yourself for Solo Sailing

How to Select Crew for a Passage or Delivery

Preparing A Boat to Sail Solo

On Watch: This 60-Year-Old Hinckley Pilot 35 is Also a Working…

On Watch: America’s Cup

On Watch: All Eyes on Europe Sail Racing

Dear Readers

Chafe Protection for Dock Lines

• Sailboat Reviews

Multihull Capsize Risk Check

Waves, squalls, and inattention to trim and helm contribute to instability..

In recent years we’ve seen a surge in interest in multihulls. Thirty years ago, when my experience with cruising multihulls began, nearly all of the skippers served an apprenticeship with beach cats, learning their quirks by the seat of their pants. They hiked out on trapezes and flew head-over-heels past their pitch-pole prone Hobie 16s, until they learned the importance of keeping weight way aft on a reach and bearing off when the lee bow began to porpoise.

By contrast, the new generation of big cat buyers skipped this learning process, learning on monohulls or even choosing a big stable cat as their first boat. Heck, nobody even builds real beach cats anymore, only pumped up racing machines and rotomolded resort toys. So we’re guessing there are a few things these first-time cruising multihull sailors don’t know, even if they have sailed cruising cats before.

It is extremely hard to capsize a modern cruising cat. Either a basic disregard for seamanship or extreme weather is required. But no matter what the salesman tells you (“none of our boats have ever …”), it can happen. A strong gust with sail up or a breaking wave in a survival storm can do it. And when a multihull goes over, they don’t come back.

Trimarans tend to be more performance oriented than catamarans. In part, this is because it’s easier to design a folding trimaran, and as a result Farrier, Corsair, and Dragonfly trimarans had a disproportionate share of the market.

In spite of this and in spite of the fact that many are raced aggressively in windy conditions, capsizes are few, certainly fewer than in equivalent performance catamaran classes.  But when they do go over, they do so in different ways.

Trimarans have greater beam than catamarans, making them considerably more resistant to capsize by wind alone, whether gusts or sustained wind. They heel sooner and more than catamaran, giving more warning that they are over powered. 

Waves are a different matter. The amas are generally much finer, designed for low resistance when sailing deeply immersed to windward. As a result, trimarans are more susceptible to broach and capsize when broad reaching at high speed or when caught on the beam by a large breaking wave.

In the first case, the boat is sailing fast and overtaking waves. You surf down a nice steep one, into the backside of the next one, the ama buries up to the beam and the boat slows down. The apparent wind increases, the following wave lifts the transom, and the boat slews into a broach. If all sail is instantly eased, the boat will generally come back down, even from scary levels of heel, but not always.

In the second case a large wave breaks under the boat, pulling the leeward ama down and rolling the boat. Catamarans, on the other hand, are more likely to slide sideways when hit by a breaking wave, particularly if the keels are shallow (or raised in the case of daggerboards), because the hulls are too big to be forced under. They simply get dragged to leeward, alerting the crew that it is time to start bearing off the wind.

Another place the numbers leave us short is ama design. In the 70s and 80s, most catamarans were designed with considerable flare in the bow, like other boats of the period. This will keep the bow from burying, right? Nope. When a hull is skinny it can always be driven through a wave, and wide flare causes a rapid increase in drag once submerged, causing the boat to slow and possibly pitchpole.

Hobie Cat sailors know this well. More modern designs either eliminate or minimize this flare, making for more predictable behavior in rough conditions. A classic case is the evolution of Ian Farrier’s designs from bows that flare above the waterline to a wave-piercing shape with little flare, no deck flange, increased forward volume, and reduced rocker (see photos page 18). After more than two decades of designing multihulls, Farrier saw clear advantages of the new bow form. The F-22 is a little faster, but more importantly, it is less prone to broach or pitchpole, allowing it to be driven harder.

Beam and Stability

The stability index goes up with beam. Why isn’t more beam always better? Because as beam increases, a pitchpole off the wind becomes more likely, both under sail and under bare poles. (The optimum length-to-beam ratios is 1.7:1 – 2.2:1 for cats and 1.2:1-1.8:1 for trimarans.) Again, hull shape and buoyancy also play critical roles in averting a pitchpole, so beam alone shouldn’t be regarded as a determining factor.

Drogues and Chutes

While monohull sailors circle the globe without ever needing their drogues and sea anchors, multihulls are more likely to use them. In part, this is because strategies such as heaving to and lying a hull don’t work for multihulls. Moderate beam seas cause an uncomfortable snap-roll, and sailing or laying ahull in a multihull is poor seamanship in beam seas.

Fortunately, drogues work better with multihulls. The boats are lighter, reducing loads. They rise over the waves, like a raft. Dangerous surfing, and the risk of pitchpole and broach that comes with it, is eliminated.  There’s no deep keel to trip over to the side and the broad beam increases the lever arm, reducing yawing to a bare minimum. 

Speed-limiting drogues are often used by delivery skippers simply to ease the motion and take some work off the autopilot. By keeping her head down, a wind-only capsize becomes extremely unlikely, and rolling stops, making for an easy ride. A properly sized drogue will keep her moving at 4-6 knots, but will not allow surfing, and by extension, pitch poling. 

For more information on speed limiting drogues, see “ How Much Drag is a Drogue? ” PS , September 2016.

Capsize Case Studies

Knock wood, we’ve never capsized a cruising multihull (beach cat—plenty of times), but we have pushed them to the edge of the envelope, watched bows bury, and flown multi-ton hulls to see just how the boat liked it and how fast she would go. We’re going to tell you about these experiences and what can be learned from them, so you don’t have to try it.

First, it helps to examine a few examples of some big multihull capsizes.

Techtronics 35 catamaran, John Shuttleworth design

This dramatic pitchpole occurred in a strong breeze some 30 years ago. In order to combine both great speed and reasonable accommodation, the designer incorporated considerable flare just above the waterline, resulting in hulls that were skinny and efficient in most conditions, but wide when driven under water in steep chop.

The boat was sailing fast near Nova Scotia, regularly overtaking waves.  The bows plowed into a backside of a particularly steep wave, the submerged drag was huge, and the boat stopped on a dime. At the same time, the apparent wind went from about 15 knots into the high 20s, tripling the force on the sails and rapidly lifting the stern over the bow. Some crew were injured, but they all survived.

PDQ 32 Catamaran

On July 4, 2010, the boat’s new owners had scheduled time to deliver their new-to-them boat up the northern California coast. A strong gale was predicted, but against all advice, they left anyway. The boat turned sideways to the confused seas and a breaking wave on the beam capsized the boat. There were no injuries, and the boat was recovered with only moderate damage a few weeks later. Repaired, she is still sailing.

Another PDQ 32 was capsized in the Virgin Islands when a solo sailor went below to tend to something and sailed out of the lee of the island and into a reinforced trade wind.

Sustaining speed with wider tacking angles will help overcome leeway.

Cruising cats can’t go to windward. That’s the rumor, and there’s a kernel of truth to it. Most lack deep keels or dagger boards and ex-charter cats are tragically under canvassed for lighter wind areas, a nod to near universal lack of multihull experience among charter skippers. Gotta keep them safe.  But there are a few tricks that make the worst pig passable and the better cats downright weatherly. Those of you that learned your craft racing Hobies and Prindles know most of this stuff, but for the rest of you cruising cat sailors, there’s some stuff the owner’s manual leaves out.

“Tune” the Mast

Having no backstay means that the forestay cannot be kept tight unless you want to turn your boat into a banana and over stress the cap shrouds. Although the spreaders are swept back, they are designed primarily for side force with just a bit of pull on the forestay. The real forestay tension comes from mainsheet tension.

Why is it so important to keep the forestay stay tight? Leeward sag forces cloth into the luff of the genoa, making it fuller and blunting the entry into the wind. The draft moves aft, the slot is pinched, and aerodynamic drag increases. Even worse, leeway (sideslip) increases, further increasing drag and sliding you away from your destination. Sailing a cruising cat to windward is about fine tuning the lift to drag ratio, not just finding more power.

How do you avoid easing the mainsheet in strong winds? First, ease the traveler instead. To avoid pinching the slot, keep the main outhaul tight to flatten the lower portion of the main. Use a smaller jib or roll up some genoa; overlap closes the slot. Reef if need be; it is better to keep a smaller mainsail tight than to drag a loose mainsail upwind, with the resultant loose forestay and clogged slot. You will see monos with the main twisted off in a blow. Ignore them, they are not cruising cats. It is also physically much easier to play the traveler than the main sheet. Be glad you have a wide one.

Check Sheeting Angles

Very likely you do not have enough keel area to support large headsails. As a result, you don’t want the tight genoa lead angles of a deep keeled monohull. All you’ll do is sail sideways. Too loose, on the other hand, and you can’t point. In general, 7-10 degrees is discussed for monos that want to pinch up to 40 degrees true, but 14-16 degrees makes more sense for cruising cats that will sail at no less than 50 degrees true. Rig up some temporary barber haulers and experiment. Then install a permanent Barber-hauler; see “ Try a Barber Hauler for Better Sail Trim ,” Practical Sailor , September 2019.

The result will be slightly wider tacking angles, perhaps 105 degrees including leeway, but this will be faster for you. You don’t have the same hull speed limit, so let that work for you. Just don’t get tempted off onto a reach; you need to steer with the jib not far from luffing.

Watch the fore/aft lead position as well. You want the jib to twist off to match the main. Typically it should be right on the spreaders, but that depends on the spreaders. If you have aft swept shrouds, you may need to roll up a little genoa, to 110% max.

Use your Tell-Tales

On the jib there can be tell-tale ribbons all over, but on the main the only ones that count are on the leech. Keep all but the top one streaming aft. Telltales on the body of sail are confused by either mast turbulence (windward side) or pasted down by jib flow (leeward side) and won’t tell you much. But if the leach telltales suck around to leeward you are over sheeted.

Keep Your Bottom Clean

 It’s not just about speed, it’s also pointing angle. Anything that robs speed also makes you go sideways, since with less flow over the foil there will be less lift. Flow over the foils themselves will be turbulent. Nothing slows you down like a dirty bottom.

Reef Wisdom

Push hard, but reef when you need to. You will have the greatest lift vs. windage ratio when you are driving hard. That said, it’s smart to reef most cruising cats well before they lift a hull to avoid overloading the keels. If you are feathering in the lulls or allowing sails to twist off, it’s time to reef.

Don’t Pinch

Pinching (pointing to high) doesn’t work for cats. Get them moving, let the helm get a little lighter (the result of good flow over the rudder and keel), and then head up until the feeling begins to falter. How do you know when it’s right? Experiment with tacking angles (GPS not compass, because you want to include leeway in your figuring) and speed until the pair feel optimized. With a genoa and full main trimmed in well, inside tracks and modified keels, and relatively smooth water, our test PDQ can tack through 100 degrees with the boat on autopilot. Hand steering can do a little better, though it’s not actually faster to windward. If we reef or use the self-tacking jib, that might open up to 110-115 degrees, depending on wave conditions. Reefing the main works better than rolling up jib.

Boats with daggerboards or centerboards.  The comments about keeping a tight forestay and importance of a clean bottom are universal. But the reduction in leeway will allow you to point up a little higher, as high as monohulls if you want to. But if you point as high as you can, you won’t go any faster than similar monohulls, and quite probably slower. As a general rule, tacking through less than 90 degrees, even though possible, is not the best strategy. A slightly wider angle, such as 100 degrees, will give a big jump in boat speed with very little leeway.

Chris White Custom 57

In November 2016, winds had been blowing 25-30 knots in stormy conditions about 400 miles north of the Dominican Republic. The main had two reefs in, and the boat was reaching under control at moderate speed when a microburst hit, causing the boat to capsize on its beam. There were no serious injuries.

Another Chris White 57 capsized on July 31, 2010. It had been blowing 18-20 knots and the main had a single reef. The autopilot steered. The wind jumped to 62 knots in a squall and changed direction so quickly that no autopilot could be expected to correct in time.

Gemini 105mC

In 2018, the 34-foot catamaran was sailing in the Gulf of Mexico under full sail at about 6 knots in a 10-15 knot breeze. Squalls had been reported on the VHF. The crew could see a squall line, and decided to run for cover. Before they could get the sails down, the gust front hit, the wind shifted 180 degrees, and the boat quickly went over.

38-foot Roger Simpson Design

The catamaran Ramtha was hit head-on by the infamous Queen’s Birthday storm in 1994. The mainsail was blown out, and steering was lost. Lacking any control the crew was taken off the boat, and the boat was recovered basically unharmed 2 weeks later. A Catalac catamaran caught in the same storm trailed a drogue and came through unharmed. Of the eight vessels that called for help, two were multihulls. Twenty-one sailors were rescued, three aboard the monohull Quartermaster were lost at sea.

15 meter Marsaudon Ts

Hallucine capsized off Portugal on November 11 of this year. This is a high performance cat, in the same general category as the familiar Gunboat series. It was well reefed and the winds were only 16-20 knots. According to crew, it struck a submerged object, and the sudden deceleration caused the boat to capsize.

Multihulls We’ve Sailed

Clearly seamanship is a factor in all of our the previous examples. The watch needs to be vigilant and active. Keeping up any sail during squally weather can be risky. Even in the generally benign tropics, nature quickly can whip up a fury. But it is also true that design choices can impact risk of capsize. Let’s see what the numbers can tell us, and what requires a deeper look.

Stiletto Catamaran

We’ve experienced a number of capsizes both racing and while driving hard in these popular 23-foot catamarans. The combination of light displacement and full bow sections make pitchpoling unlikely, and the result is very high speed potential when broad reaching. Unfortunately, a narrow beam, light weight, and powerful rig result in a low stability factor. The potential for capsize is real when too much sail is up and apparent wind is directly on the beam. The boat can lift a hull in 12 knots true. This makes for exciting sailing when you bring your A-game, but limits the boat to coastal sailing.

Corsair F-24 MK I trimaran

Small and well canvased, these boats can capsize if driven hard (which they often are), but they are broad beamed, short-masted, and designed for windy sailing areas. F-24s are slower off wind than the Stiletto, in part because of greater weight and reduced sail area, but also because the main hull has more rocker and does not plane as well. They are faster to weather and point considerably higher than a Stiletto (90-degree tacking angle vs. 110 degrees). This is the result of greater beam, a more efficient centerboard design, and slender amas that are easily driven in displacement mode. The boat is quite forgiving if reefed.

Going purely by the numbers, this boat seems nearly identical to the F-24. In practice, they sail quite differently. The Dash uses a dagger board instead of centerboard, which is both more hydrodynamic and faster, but more vulnerable to damage if grounded at high speed.

The rotating mast adds power that is not reflected in the numbers. The bridgedeck clearance is higher above the waterline, reducing water drag from wave strikes. The wave-piercing amas create greater stability up wind and off the wind. The result is a boat that is slightly faster than the original F-24 and can be driven much harder off the wind without fear of pitchpole or broach.

Without proper testing, calculating stability yields only a rough picture.

Evaluating multihull performance based on design numbers is a bit more complicated than it is with ballasted, displacement monohulls, whose speed is generally limited by hull form. [Editor’s note: The formula for Performance Index, PI has been updated from the one that originally appeared in the February 2021 issue of Practical Sailor.

The following definitions of units apply to the adjacent table:

SA = sail area in square feet

D (displacement) = weight in pounds

LWL = length of waterline in feet

HCOE = height of sail center of effort above the waterline in feet

B = beam in feet

BCL = beam at the centerline of the hulls in feet.

Since a multihull pivots around the centerline beam, the overall beam is off the point and is not used in formulas. Calculate by subtracting the individual hull beam from the overall beam.

SD ratio = SA/(D/64)^0.66

This ratio gives a measure of relative speed potential on flat water for monohulls, but it doesn’t really work for multihulls.

Bruce number = (SA)^0.5/(D)^0.333

Basically this is the SD ratio for multihulls, it gives a better fit.

Performance index = (SA/HCOE)^0.5 x (D/1000)^0.166

By including the height of the COE and displacement, this ratio reflects the ability of the boat to use that power to sail fast, but it understates the importance of stability to the cruiser.

Stability factor = 9.8*((0.5*BCL*D)/(SA*HCOE))^0.5

This approximates the wind strength in knots required to lift a hull and includes a 40% gust factor. In the adjacent data sheet, we compare the formula’s predicted stability to observed behavior. Based on our experience on the boats represented, the results are roughly accurate.

Ama buoyancy = expressed as a % of total displacement.

Look for ama buoyancy greater than 150% of displacement, and 200 is better.  Some early trimaran designs had less than 100 percent buoyancy and would capsize well before flying the center hull. They exhibited high submerged drag when pressed hard and were prone to capsize in breaking waves.

Modern tris have ama buoyancy between 150 and 200 percent of displacement and can fly the center hull, though even racing boats try to keep the center hull still touching. In addition, as a trimaran heels, the downward pressure of wind on the sail increases, increasing the risk of capsize. The initial heel on a trimaran is more than it is on catamarans, and all of that downward force pushes the ama even deeper in the water. Thus, like monohulls, it usually makes sense to keep heel moderate.

These numbers can only be used to predict the rough characteristics of a boat and must be supplemented by experience.

This is the first real cruising multihull in our lineup. A few have capsized. One was the result of the skipper pushing too hard in very gusty conditions with no one on watch. The other occurred when a crew unfamiliar with the boat ignored local wisdom and set sail into near gale conditions.

Although the speed potential of the PDQ 32 and the F-24 are very similar, and the stability index is not very different, the feel in rough conditions is more stable, the result of much greater weight and fuller hull sections.

Like most cruising cats, the PDQs hulls are relatively full in order to provide accommodation space, and as a result, driving them under is difficult. The increased weight slows the motion and damps the impact of gusts. Yes, you can fly a hull in about 25 knots apparent wind (we proved this during testing on flat water with steady winds), and she’ll go 8-9 knots to weather doing it, but this is not something you should ever do with a cruising cat.

Stability by the Numbers

The “stability factor” in the table above (row 14) is based on flatwater conditions, and ignores two additional factors. Unlike monohulls, the wind will press on the underside of the bridgedeck of a multihull once it passes about 25 degrees of heel, pushing it up and over. This can happen quite suddenly when the boat flies off a wave and the underside is suddenly exposed to wind blowing up the slope of the wave. A breaking wave also adds rotational momentum, pitching the windward hull upwards.

Multihulls by the Numbers

Autopilot is a common thread in many capsizes. The gust “came out of no place…” No it didn’t. A beach cat sailor never trusts gusty winds. The autopilot should be disengaged windspeeds and a constant sheet watch is mandatory when gusts reach 30-40 percent of those required to fly a hull, and even sooner if there are tall clouds in the neighborhood. Reef early if a helm watch is too much trouble.

“But surely the sails will blow first, before the boat can capsize?” That would be an expensive lesson, but more to the point, history tells us that well-built sails won’t blow.

“Surely the rig will fail before I can lift a hull?” Again, that could only be the result of appallingly poor design, since a rig that weak will not last offshore and could not be depended on in a storm. Furthermore, good seamanship requires that you be able to put the full power of the rig to work if beating off a lee shore becomes necessary.

Keeping both hulls in the water is up to you. Fortunately, under bare poles and on relatively flat water even smaller cruising cats can take 70 knots on the beam without lifting … but we don’t set out to test that theory, because once it blows for a while over even 40 knots, the real risk is waves.

Everything critical to safety in a blow we learned on beach cats. Like riding a bike, or—better yet—riding a bike off-road, there are lessons learned the hard way, and those lessons stay learned. If you’ve been launched into a pitchpole a few times, the feeling you get just before things go wrong becomes ingrained.

Perhaps you are of a mature age and believe you monohull skills are more than enough to see you through. If you never sail aggressively or get caught in serious weather, you’re probably right.

However, if there’s a cruising cat in your future, a season spent dialing in a beach cat will be time well spent. Certainly, such experience should be a prerequisite for anyone buying a performance multihull. The statement might be a little pointed, but it just makes sense.

Capsize by Wind Alone

Capsizing by wind alone is uncommon on cruising multihulls. Occasionally a performance boat will go over in squally weather. The crew could easily have reefed down or gone to bare poles, but they clung to the idea that they are a sail boat, and a big cat feels so stable under sail—right up until a hull lifts.

Because a multihull cannot risk a knockdown (since that is a capsize), if a squall line is tall and dark, the smart multihull sailors drops all sail. Yes, you could feather up wind, but if the wind shifts suddenly, as gusts often do, the boat may not turn fast enough. Off the wind, few multihulls that can take a violent microburst and not risk a pitchpole. When a squall threatens, why risk a torn sail for a few moments of fast sailing?

You can’t go by angle of heel alone because of wave action. Cat instability begins with the position of the windward hull. Is it flying off waves?

A trimaran’s telltale is submersion of leeward ama. Is the leeward ama more than 30-40 percent under water? The maximum righting angles is a 12-15 degrees for cats and 25-30 degrees for trimarans, but that is on flat water. Once the weather is up, observation of motion becomes far more important. Is the boat falling into a deep trough, or is at about to launch off a steep wave and fly?

Just as monohulls can surprise a new sailor by rounding up and broaching in a breeze, multihulls have a few odd habits that only present themselves just before things go wrong. Excuse the repetition, but the best way to learn to instinctively recognize these signs is by sailing small multihulls.

Sailing Windward

Because of the great beam, instead of developing weather helm as they begin to fly a hull, multihulls can suddenly develop lee helm, causing the boat to bear away and power up at the worst possible moment. This is because the center of drag moves to the lee hull, while the center of drive remains in the center, causing the boat to bear away.

If the boat is a trimaran, with only a center rudder, this rounding up occurs just as steering goes away. This  video of a MOD 70 capsize shows how subtle the early warning signs can be ( www.youtube.com/watch?v=CI2iIY61Lc8 ).

Sailing Downwind

Off the wind, the effect can be the reverse. The lee hull begins to bury, and you decide it is time to bear off, but the submerged lee bow acts like a forward rudder. It moves the center of effort far forward and prevents any turn to leeward.  Nearly all trimarans will do this, because the amas are so fine. The solution is to bear away early, before the ama buries­—or better yet, to reef.

Conclusions

We’re not trying to scare you off multi-hulls. Far from it. As you can probably tell, I am truly addicted. Modern designs have well-established reputation seaworthiness.

But multihull seaworthiness and seamanship are different from monohulls, and some of those differences are only apparent when you press the boat very hard, harder than will ever experience in normal weather and outside of hard racing. These subtle differences have caught experienced sailors by surprise, especially if their prior experience involved only monohulls or cruising multihulls that were never pressed to the limit.

Although the numbers only tell part of the story, pay attention to a boat’s stability index. You really don’t want an offshore cruising boat that needs to be reefed below 22-25 knots apparent. Faster boats can be enjoyable, but they require earlier reefing and a more active sailing style.

When squalls threaten or the waves get big, take the appropriate actions and take them early, understanding that things happen faster. And don’t forget: knockdowns are not recoverable. It is satisfying to have a boat that has a liferaft-like stability, as long as you understand how to use it.

Technical Editor Drew Frye is the author of “Rigging Modern Anchors.” He blogs at www.blogspot/sail-delmarva.com

RELATED ARTICLES MORE FROM AUTHOR

22 comments.

It’s interesting to read the report of the Multihull Symposium (Toronto, 1976) regarding the issues of multihull capsize in the formative years of commercial multihull design. There were so many theories based around hull shape, wing shape, submersible or non submersibe floats, sail area and maximum load carrying rules. My father, Nobby Clarke, of the very successful UK firm Cox Marine, fought many a battle in the early Sixties with the yachting establishment regarding the safety of trimarans, and I am glad that in this modern world technolgy answers the questions rather than the surmises of some establishment yachting magazines of the time.

Thank You Mr.Nicholson and Thank You to Practical Sailor for this great read superbly shared by Mr.Nicholson God bless you and our great Sailing Family.

Great read! Multi hulls are great party vessels which is why companies like Moorings and Sunsail have larger and larger numbers in their fleets. More and more multihulls are joining the offshore sailing fleets. Dismasting and capsizes do happen. Compared to mono hulls I know of no comparative statistics but off shore and bluewater, give me a mono hull. That is probably because I took one around with zero stability issues and only minor rig few issues. Slowly though; ten years.

Great read! Multi hulls are great party vessels which is why companies like Moorings and Sunsail have larger and larger numbers in their fleets. More and more multihulls are joining the offshore sailing fleets. Dismasting and capsizes do happen. Compared to mono hulls I know of no comparative statistics but off shore and bluewater, give me a mono hull. That is probably because I took one around with zero stability issues and only minor rig issues. Slowly though; ten years.

What’s an ama? Those who are new to sailing or even veteran sailors who have never been exposed to a lot of the terms simply get lost in an article with too many of those terms. I would suggest putting definitions in parentheses after an unfamiliar term to promote better understanding.

Vaka is the central, main hull, in a trimaran.

Ama is the “pontoon” hull at the end of the aka, or “crossbeam”, on each side of a trimaran.

I’m a geek, and therefore live in a dang *ocean* of the Jargonian & Acronese languages, and agree with you:

presuming 100% of audience is understanding each Jargonian term, and each Acronese term, is pushing credulity…

( and how in the hell “composition” means completely different things in object-oriented languages as compared with Haskell?? Bah. : )

As I understand it: Cats have an advantage in big beam seas because they will straddle a steep wave whereas a Tri can have its main hull on the wave crest with the windward ama’s bottom very high off the water and acting as another sail. Also, rig loads on a mono hull are calculated to be 2.5-3x the righting moment at a 45 deg heal; the reason being at 45 degrees the boat will still be making headway and feeling the dynamic loads in the seaway but beyond 45 degrees is a knockdown condition without seaway shock loads. A multihull rig on the other-hand can experience very high dynamic shock loads that are too short in duration to raise a hull.

Though I agree with much of the article content, the statement: “… this is because strategies such as heaving to and lying a hull don’t work for multihulls.” does not ring true in my experience. I have sailed about 70,000nm on cruising catamarans, a Canadian built Manta 38 (1992, 39ft x 21ft) with fixed keels and my present boat, a Walter Greene Evenkeel 38 (1997, 38ft x 19ft 6″) with daggerboards. I came from a monohull background, having circumnavigated the world and other international sailing (60,000nm) on a mono before purchasing the Manta cat. I owned that catamaran for 16 years and full time cruised for seven of those years, including crossing the Arctic Circle north of Iceland and rounding Cape Horn. I usually keep sailing until the wind is over 40knots, then the first tactic is to heave-to, and have lain hove-to for up to three days with the boat lying comfortably, pointing at about 50 to 60degrees from the wind and fore-reaching and side-slipping at about 1.5 to 2knots. Usually once hove-to I wait until the wind has reduced to 20knots or less before getting underway again. Lying ahull also works, though I have only used that in high winds without big breaking waves, as in the South Atlantic in the lee of South America with strong westerlies. I have lain to a parachute sea anchor and it is very comfortable, though lots of work handling all that gear and retrieving it and was glad to have deployed it when I did. I heave-to first, then deploy the sea anchor from the windward bow while in the hove-to position. The daggerboard cat will also heave-to well, though takes some adjusting of the boards to get her to lay just right, though I have not experience being at sea on this boat in as high of winds as with the Manta (over 60 knots). Catamaran bows have lots of windage and have little depth of hull forward. Thus you need mostly mainsail and little jib to keep her pointing into the wind. I aim for the wind to blow diagonally across the boat, with a line from the lee transom to the windward bow pointing into the wind as an optimum angle. As per taking the boat off autopilot when the wind gets near 20 knots is just not practical. The longest passage I have made on my catamarans has been from Fortaleza, Brazil, to Bermuda, nearly 3,000nm and across the squall prone doldrums and horse latitudes, taking 20 days. The autopilot steered the whole distance. I have never lifted a hull nor felt the boat was out of control despite having sailed in some of the most dangerous waters of the world.

I believe that your Techtronics 35 should be Tektron 35 (Shuttleworth) and as far as I know the capsize that occurred off Nova Scotia was, in fact, a Tektron 50 (Neptune’s Car I believe) sailed by the Canadian builder Eugene Tekatch and was reported as being off PEI. This capsize was well documented under a thread in “Steamradio” that I can no longer find. It appears that Steamradio is now, unfortunately, no longer operating. The report of the capsize was along the lines of the boat being sailed off wind with all sail in a gale. I think Shuttleworth indicated that they would have been doing about 30 knots. They then hit standing waves off PEI, the boat came to a standstill and with the change in apparent wind to the beam, over they went. Reading between the lines, Shuttleworth was pretty unhappy that one of his designs had been capsized in this manner, unhappier yet that some of the findings of I believe an american committee/ board were that the design was somehow at fault. Given Shuttleworth’s rep it seems unlikely. As I say these are recollections only.

Shortly afterwards Neptune’s Car was up for sale for a steal price.

I think Jim Brown (Trimaran Jim) when speaking of the Tektron 50 referred to it as weighing less than similarly sized blocks of Styrofoam. Admittedly, blocks of solid foam weigh more than one might imagine, but still a vivid point. Though Tektron 50 was light, we have far more options to build lighter boats today, than in the past.

Good that Practical Sailor is looking at this issue and I agree with much of it, so thanks PS for that. Also fun to see Nobby Clark’s son chip in …. I met Nobby at the ’76 World Symposium in Toronto, when I was just starting to get interested in Trimarans. I have since owned 4 and as a naval architect, builder and sailor, now specialize in their design and ‘all things related’, with a quasi-encyclopedic website at: http://www.smalltridesign.com . So as a trimaran guru, I’d like to add a few things here. In my experience (now 45 years with multis) there is really too much difference between catamarans and trimarans to compare them on the basis of the same formulas. For example, lifting a hull on a cat brings about a major reduction in reserve stability ….. lifting an ama on a trimaran, certainly does not. Using 30-40% immersion of an ama is hardly a guide to limit or prevent a capsize on a trimaran as that’s not even close to normal operating immersion . I would recommend a reduction of ama bow freeboard to about 1-2% of the boat length (depending on a few size factors) is a better guide as the ‘time to really ease up’. This visual indicator is great on my boats but is very hard to judge on hulls with reverse bows where there is no deck up forward. For a number of reasons, I am against this shape but as I’ve already made my case on line about this, I’ll not repeat it here. Over 80% of the capsizes we see on line, show that mainsails were never released .. and that includes the capsize of the MOD70 in the YouTube referenced in the PS article. As several trimaran owners I deal with have also capsized or near-capsized their boats (particularly those between 22 and 40ft that ‘feel’ more stable than they really are, I am developing a few models of EMRs to help solve their issue, (EMR=Emergency Mainsheet Release) and these will be operated wirelessly by punching a large button under the skippers vest, as I am not in favor of any fully automatic release. This HAS to be a skippers decision in my opinion for numerous reasons. The first two units of this EMR dubbed ‘Thump’R, will be installed this Spring … one in Europe and the other in Australia, but one day, perhaps Practical Sailor will get to see and test one for you 😉 In a few words, my advice to all multihull sailors is to be very aware of the way your stability works on your specific boat and sail accordingly. We learn this instinctively with small beach boats, but is harder to ‘sense’ as boats get heavier and larger. I have sailed cats from a 60ft Greene cat to a 12ft trimaran and although some basics apply they are of course very different. But you still need to ‘learn the early signs’ of your boat, as these must be your guide. IMHO a good multihull design will be fairly light and easily driven which means that it will still sail well with less sail. This means that the use of a storm mainsail in potentially high wind can add much reserve stability and safety to your voyage. To give an example from my small W17 design that sets a rotating wingmast, the boats top speed to date is 15kts with 200 sqft, but with the storm mainsail and a partly-furled jib I can get the area down under 100sqft without losing rig efficiency. In fact, the tall narrow storm main with a 5.5:1 aspect ratio is now even MORE efficient as the wingmast is now doing a higher percentage of the work. In 25-30t storm conditions, I have now sailed 8kts upwind and 14.4kts down, and feel very dry and comfortable doing so … even at 80+. So get the right sails, and change down to small more efficient ones when it pipes up. A multihull storm sail should look nothing like a mono’s trysail … with our narrow hulls, we are sailing in a very different way. Happy sailing Mike

In the old days, low displacement, short and narrowly spaced amas were the design of choice. One was supposed to back off when they started to submerge. It was a visual indicator. Modern amas are huge. If a 24 foot tri like the Tremolino could be designed to use Hobie 16 hulls in the 70s, today it would carry Tornado hulls. The slippery shape of designs catches the eye, and their supposed less grabby when submerged decks, but these amas also carry 1.5-2x main hull displacement. The chance of burying them is significantly reduced.

The original intent of these slippery ama designs was to shake off wind. Though low drag shapes for reducing pitch pole risk are a consideration, it should be balanced against maintaining ama deck walkability. This is important in allowing one to service the boat or rig drogues or anchors, not to mention to position live ballast. I am thinking here of the smaller club and light crusing tris. You aren’t going to be able to do a lot of these things on monster luxury boats that are a different scale entirely. But they mater on the kinds of boat most people are likely to own.

Poring over tri design books, one will notice that the silhouette of, say, a 40 foot tri, and the smaller 20 foot design are very similar This yields a doubling of the power to weight ratio on the smaller boat. This difference can even be greater as the smaller boats are often nothing more than empty shells, yet may carry higher performance rig features like rotating masts. Smaller tris are often handicapped by the requirements of being folded for trailering which both limits beam and ama displacement, though it may tend to increase weight. On top of that, mainsail efficiency is much higher, these days, with squared shapes, and less yielding frabrics. And, of course, much larger sail plans. All the better, just so long as people realize what they have by the tail.

Excellent article…thank you!!!!!!!!!

Good article. One thing that concerns me about modern cruising cat is how far above water level the boom is. I first noticed this looking at Catana 47’s for hire in New Caledonia and recently saw large Leopards 48 & 50 footers visiting Fremantle Sailing Club, here in Australia, and in all cases the boom seems to be at least 20 feet (6 metres) above the water. This seems to greatly increase the heeling moment and reduce the amount of wind required to capsize the vessel. Mind you at 20+ tons, the weight of the Leopards probably makes them a bit more resistant to capsize. But why does the rig need to be so far off the water?

Notice to Moderator After having read this article a couple or days back, I emailed naval architect mike waters, author of the specialist website SmallTriDesign to read the article and perhaps comment. Nearly a day ago, he emailed me back to say that he had, yet there’s been nothing posted from him and now I see a post with todays date. With his extensive knowledge and experience I would have thought his insight to be valuable to your readers and I was certainly looking forward to seeing his input. What happened?

Yes, PS .. what’s cookin ? Thought readers would be interested to know that capsize control help maybe on the way 😉

Yes PS, what’s cookin’ ? Thought your readers would like to know that some anti-capsize help maybe on the way 😉

Great article! I’ve read it twice so far. Recently in Tampa Bay I sailed my Dragonfly 28 in 25 knots breeze and found that speed was increased (drag reduced?) after I put in one reef in the main. I think I should have reefed the Genoa first?

Absolutely Tim. Slim hulls, as for most trimarans and the finer, lighter catamarans will often sail more efficiently with less sail .., especially if with a rotating mast, and you can indeed get proportionally better performance. The boat sails more upright for one thing, giving more sail drive from improved lift/drag and less hull resistance .. and its certainly safer and more comfortable and can also be drier, as an upright boat tends to keep wavetops passing underneath more effectively. Even my W17 design has been shown to achieve over 90% of its top speed with only 1/2 the sail area, by switching to a more efficient, high-aspect ratio ‘storm mainsail’ set behind its rotating wingmast …, a far cry from a monohulls storm trysail in terms of upwind efficiency. Yes, wind speed was higher, but the boat sailed far easier and its definitely something that slim hulled multihulls should explore more, as they will then also be less likely to capsize. More here if interested http://www.smalltridesign.com

Darrell, is there some reason for blocking replies that hold opinions contrary to those of PS ? I am still hoping to read the expertise of those who actually study design and sail multihulls. The written target of PS is to accurately present facts and that implies the input of experts. Over the last 10 years, I have come to appreciate a few experts in the field of multihulls and right now, I see at least one of them is not being given a voice here. Your article made a lot of fine points but there are some issues needing to be addressed if PS it to remain a trusted source for accurate information. First, I have been told by a reliable source, you need to separate trimarans from catamarans and use different criteria to compare their stability as they do not respond the same and neither can you judge their reserve stability in the same way. I would also like to know what NA Mike Waters was hinting at when he said “capsize control help may be on the way” .. would you know anything about that? If not, then please invite or allow him space or the promise of PS fact-finding accuracy is heading down the drain for me. thanks

As a new subscriber to PS, it is a little disquieting to see no response to the two comments above by Tom Hampton.

LEAVE A REPLY Cancel reply

Log in to leave a comment

Latest Videos

What’s the Best Sailboats for Beginners?

Why Does A Sailboat Keel Fall Off?

The Perfect Family Sailboat! Hunter 27-2 – Boat Review

Pettit EZ-Poxy – How to Paint a Boat

Latest sailboat review.

• Privacy Policy
• Do Not Sell My Personal Information
• Online Account Activation
• Privacy Manager

Farrier International

a Division of Daedalus

FARRIER FOLDING SYSTEM™

One key to the success of Farrier trimarans is the easy trailerability made possible by the unique Farrier Folding System ™.

The Farrier system is the most structurally sound trimaran folding system available, with no hinges in the beams or the critical beam to float join, while corrosion prone wires are never used in structurally critical areas. Overall beam can be varied in seconds, by just one person, anywhere.

After 33 years of use world wide the Farrier System is well proven, the most successful folding system, and used by more trimarans than anything else. So to be safe, be sure to insist on the genuine twin strut ‘Farrier Folding System’™. It is significantly different from all the rest, and the many advantages can be summarized as follows:

• Folds for road legal trailering in minutes without any heavy assembly being required.
• The twin strut folding system gives absolute control over movement
• No need for water to support floats while folding – the twin struts make it easy to fold anywhere
• The correct folding strut geometry means folding can be done by one person, anywhere.
• Twin struts mean the float will not fall on the ground if folding out of the water on a trailer
• Absolutely no weak hinge points in the actual beams, with the highly stressed beam to float join being solid
• Absolutely no sliding parts that can bind or jam
• Corrosion prone wires are not used in structurally critical areas where sudden failure could threaten the boat
• The structurally critical lower struts are solid Aluminum 6061 T6 bar, with absolutely no butt welds.
• Custom made reinforced acetal (plastic) bushes insulate aluminum struts from stainless steel pivot pins
• There is no reliance on the rig for structural support should float reverse loading occur
• Beams are structurally sound no matter how loaded, including even after a capsize
• Proven track record, with 33 years development, six Atlantic crossings and race records/wins world wide.
• Now used by over 3000 boats world wide

Trimaran - Multihull Component Terms

Multihull Component Terms

There are three terms that describe the components of modern multihulls. The term vaka , like the related terms aka and ama, come from the Malay and Micronesian language group terms for parts of the outrigger canoe, and vaka can be roughly translated as canoe or main hull.

• Vaka - A proa consists of a vaka, the main canoe-like hull; an ama, the outrigger; and akas, the poles connecting the ama to the vaka.
• Aka - The aka of a multihull sailboat is a member of the framework that connects the hull to the ama(s) (outrigger). The term aka originated with the proa, but is also applied to modern trimarans.
• Ama - The term ama comes from the proa. The vaka is the main hull, the ama is the outrigger, and the aka or iako (Hawaiian) is the support connecting the two (not three) hulls. The term ama and aka have been widely applied to modern trimarans.

Semantically, the catamaran is a pair of Vaka held together by Aka , whereas the trimaran is a central Vaka , with Ama on each side, attached by Aka .

The above section reflects American usage. In the UK the main hull of a trimaran is called simply the main hull or centre hull . The side hulls are floats . The structures between the main hull and the floats are called the wings and the structural portions thereof are beams . In cruising trimarans the wings are solid and cabin accommodation extends over them, while in racing trimarans accommodation is limited to the main hull and the wings are open sheets of netting.

Read more about this topic:  Trimaran

Famous quotes containing the words component and/or terms :

“ ... no one knows anything about a strike until he has seen it break down into its component parts of human beings. ” — Mary Heaton Vorse (1874–1966)

“ Talleyrand said that two things are essential in life: to give good dinners and to keep on fair terms with women. As the years pass and fires cool, it can become unimportant to stay always on fair terms either with women or one’s fellows, but a wide and sensitive appreciation of fine flavours can still abide with us, to warm our hearts. ” — M.F.K. Fisher (b. 1908)

• Symmetric Hulls

• AMERICA'S CUP
• CLASSIFIEDS
• NEWSLETTERS
• SUBMIT NEWS

Black Marlin: Jan Andersen's awesome 10m Carbon-Fibre Trimaran

Related Articles

Upcoming Events

Choosing the right beam for a multihull

QUESTION:   When assessing or designing a trimaran or catamaran, what guidance can you give to guide the choice of beam ?             

                    Lech K:  Gdansk, PL

ANSWER: An interesting question as we do see quite a variation on existing boats.

First, let’s call the Overall Beam to Length ratio B/L and the individual hull length to hull beam, L/b .

Here are a few basics to consider as inputs to your overall beam choice.

*    More beam gives more transverse stability, permitting a powerful rig to drive a boat faster, but also,       excessive beam tends to lower diagonal stability so increasing pitch-poling.    More beam also tends to allow more  fore & aft pitching.

*    More beam requires stronger connecting beams (called akas on trimarans), aggravated by the two hulls potentially being now be in different waves

*    More beam can be a problem in a marina where space is increasingly limited

*    Folding trimarans can be limited in beam due to geometric space when folded, such as:     

Transverse folding system (Farrier etc) are limited by how far down the hulls can be managed when folded.  

Swing-arm folding is limited by the overall length increase when folded.

          Hinge & latch systems are limited by what height and weight can be lifted  

*    Less beam allows a boat to heel more, thereby reducing sail exposure to side wind.

*   Less beam brings the hulls closer together, reducing beam strength requirements and weight, but potentially adding to resistance from hull-flow interaction.

*   Hulls with a high L/b ratio can be closer together than hulls with a low L/b ratio if overall stability permits.

*   As smaller boats need proportionally more displacement due to crew and structural weight, they cannot have a very high L/b ratio as they then have insufficient displacement.

------------------------------------------------------------------------------------------------------------------------------

So what do all these points finally lead to ?      Well, let’s see.

For Catamarans , the sweet spot seems to be with a L/B of 2 to 2.1.

If the beam is excessively increased, pitching and reduced diagonal stability (see dwg) start to become an issue and when such boats are lengthened to make their L/B slightly above 2, they generally become faster and have less negative issues ... but over about 2.3, their relatively lower transverse stability then starts to kick back.  

If the beam is decreased, stability drops quickly and one may start to also add wave interference between the hulls unless the boat is very light with slim hulls.

Of course, this is a simplification of things as top weight, windage, wing clearance, center of gravity, sail plan, etc etc .. all have their effects, though individually less than the important L/B ratio.

Let me give you an example of how other design criteria can move things from what may initially seem the ideal.  

Beam also has a huge effect on stability.   But the designer Jan Gougeon (then of West Systems) was an inventive guy, so he approached this design in a non-conventional way.   To achieve his first criteria .. “a fast non demountable weekend catamaran”, he needed to address the obvious lack of stability in other ways.  A low rig could work with low weight, that would then allow very slim, fast hulls.   Then he added water ballast to help keep the windward side down …. and finally, a masthead float to prevent the boat from turning turtle, where she would stay like virtually all other multihulls do IF that happens.  In this case, it was rather often as unfortunately, most sailors were not ready to adapt to this new way of sailing and with capsizes happening too quickly for most, only a dozen or so were sold.  But I did get to try the boat and felt the concept did work in the sense that the boat IS fast and also comfortable & dry, as with such long, narrow hulls, there is very little disturbance of the surface water so spray is minimal and even if the hulls are pretty close, they are too slim to create any significant cross-hull wake- interference. 

To keep the rig low (mast is shorter than the boat), she uses 2 foresails that can be furled up fast.   Those that still own one have learned to understand them and can enjoy their merits … but this is not a boat with reserve stability for sudden gusts, so you need to sail this boat more like a race dinghy and also reduce sail early.  This further means that sailing at night when you cannot see squall warnings in the sky is best avoided unless the stars are truly out for you.

But it IS an example of thinking WAY outside the box .. even if the result is not for everyone.   So ‘sweetspot L/B ratios’ do not necessarily mean they give the only solution .. just that you, as a designer, also need to work differently around the rest of the design to solve the issues you might create if you are well outside the norm.    

The lesson here is:  If you choose to go outside the norm, fully understand the implications and work around them.  You cannot ignore them and still expect success. If the designer failed at all with this radical G32 design, it was in not sufficiently educating new owners of the different sailing nuances needed to keep the boat on its feet.

For Trimarans, my studies and observations show that the preferred B/L ratio changes with boat size. 

To some degree, the same effect on diagonal stability (as for Cats) will occur with excessive beam, but with a trimaran, the two hulls in the water will be closer so it’s also important to allow for good flow between them.  So as very large racing tris can have slimmer hulls due to great length and low weight, they can have proportionally lower B/L ratios than smaller boats that need proportionally fatter central hulls just to support the displacement they need.  After all, we cannot just change things in proportion, because the weight of things (such as crew, structure etc) will not automatically get smaller for a smaller boat .. in fact it proportionally and typically, gets greater!    So smaller multihulls can often be harder to design than larger ones, where you have more space and volume to work with.    The above observations led me to plot data from good boats and create this simple little formula that fits their B/L curve pretty well.

Here is what the curve gives as a recommended B/L ratio for a sailing trimaran

                            (Sailing Trimaran) B/L ratio  = 1.48 ÷ (L  ^ 0.21)        [ Length L in feet ].

While this may initially look complex to calculate for some, it’s very easy with the right help.  Download the Mobi Calculator on your phone or tablet.  You can then add the expression x n to your basic calculator by first hitting the 3 dots [ ... ] that brings you to the Scientific Options, and then   clicking on [ x n ] that will add this feature to your basic calculator.    You can now enter the formula exactly as written, typing 1.48 ÷ (  your L value , and then x n and finally 0.21 and the closing bracket ) and then ‘ = ‘.

If you enter say L = 17 , it will give you a B/L ratio of 0.816, closely matching a W17 , while for an L of 100 ft, it will give you a B/L of only 0.562, closely matching a big ocean racing tri like Sodeb’O.

While of course you can go outside the calculated ratio, IMHO you should have a very good reason and specific justification for a deviation of more than 15% either way.   Use the list at the beginning of this article to justify your change.

For both Tris and Cats, there may be other factors that will change your design, but this gives a good starting and target point that’s based on both practical and justified design needs.

Enjoy …. playing with figures is fun ;)

mike … march 2022

ADDED NOTE ... re MOTOR MULTIS

As noted, the above ratios refer to Sailing Craft.  Without the heeling force of a sail, pure motor-tris and cats are not bound by the same needs.

A motor catamaran can have less beam, with a clean flow between the hulls now taking prominence over high beam for sailing stability, so L/B ratios of 2.5 to 3 are now more appropriate.

Hulls may need to be asymmetrical with a straighter side on the inside to avoid unfavorable hull wave interaction between them.

For a powered trimaran , overall beam should also be reduced or the motion will become uncomfortable.  (With a sailing tri, the boat is heeled with one ama out, but with a motor tri, all three hulls are immersed so wave action on the boat would be too severe if the boat is too wide) .    Amas (pontoons) now need to be narrow but deep, as a slow gentle roll of slightly greater amplitude, is more comfortable than a short quick one.  These amas (now only 40-50% of the main hull length), seem best with their center about 60-70% aft of the main hull length and need to be of fine section and relatively deep with the connecting bridge arched high above any waves, so that neither ama or aka-bridge will slam when re-entering a wave.  L/b ratios of all 3 hulls can be at their most efficient, namely 13-16 at the waterline.   The amas are now more like permanent training wheels and with a much longer central hull and no heeling force from sails, diagonal stability is no longer something to consider.    Overall beam will depend on maintaining a clean flow between the main hull and the shorter slim amas, that need to extend well down into the water, so that motion is acceptable in waves.   Typical overall B/L ratios might now be down around 0.4, becoming even less as boat design gets bigger, provided the center of gravity is kept low.

"New articles, comments and references will be added periodically as new questions are answered and other info comes in relative to this subject, so you're invited to revisit and participate." —webmaster

"See the Copyright Information & Legal Disclaimer page for copyright info and use of ANY part of this text or article"