feathering propellers for sailboats

Yachting Monthly

• Digital edition

Folding and feathering propeller test

• Emrhys Barrell
• March 24, 2015

Which is the best folding or feathering propeller for your boat? Emrhys Barrell compares 15 props in a test of speed, thrust, drag, stopping speed and propwalk

in 2009, Yachting Monthly tester Emrhys Barrell put 15 folding and feathering props through the most comprehensive test ever Credit: Graham Snook/YM

What’s the difference between a bucket and a fixed, three-bladed propeller? Not much, if you want to slow your boat down by at least half a knot when you are sailing. That’s the conclusion of our fixed, folding and feathering propeller test – the most detailed ever conducted as far as we are aware. A fixed three-bladed prop, locked in gear, exerts as much drag as hanging a bucket over the stern.

So what is the solution if you don’t want to sacrifice precious speed? The answer is, fit one of the many folding or feathering props on the market. But which one, and what are the drawbacks?

We measured the force generated by each propeller across the engine’s rev range

We tested all the props we could get our hands on (except the Volvo, Radice and J-Prop, which turned up too late for the test), measuring top speed under power, thrust (bollard pull) ahead and astern, stopping distance, and – for the first time anywhere – we measured the side-force (propwalk) generated when you put the engine into reverse.

We also measured propwalk while running astern. It’s a lot stronger than you think

It is this vital, unwanted component that sends you swinging off to one side when you try to stop suddenly, or back-up in the marina. We then towed three typical props behind a test boat to measure their drag, and how it compares to the overall drag of a yacht under sail.

Prop drag has been an issue for sailing vessels since the propeller was invented. Early trials were carried out on English warships, using jointed shafts that could be lifted into a trunk in the hull when sailing. In the 1890s, Danish pilot boats used similar lifting shafts.

For many years, long keels reduced the drag of two-bladed props on yachts, but the advent of the fin keel and exposed shafts brought the problem back again, with the added factor of more powerful engines making three-bladed props a necessity. The need to manoeuvre precisely in tightly packed marinas and overcrowded harbours has convinced even the owners of many long-keeled yachts to fit three-bladed props.

1970s: the first folding props

Most cruising skippers simply ignored the unwanted drag and loss of speed, but in racing circles it became increasingly significant. This led to the development in the 1960s and 70s of propellers whose blades folded backwards when sailing, reducing the drag markedly. The blades flew out under centrifugal force when the engine was put into ahead or astern. The earliest folding props had blades that moved independently, but this could lead to the lower blade dropping down when sailing, so the roots of the blades were linked with geared teeth, ensuring that they opened and closed together.

At the same time, an alternative approach was developed: the feathering propeller. Here, the blades were set at right-angles to the boss, as in a conventional prop, but on swivelling hubs. When motoring, the blades swing to the ahead or astern angled position, but under sail they ‘feather’, turning parallel to the boss.

One great advantage of feathering props is that they’re suitable for the many fin-and-skeg and long-keel yachts that have a small prop aperture in the rudder, where a folding prop won’t fit.

In the earliest feathering props, the blades remain in the same orientation to the boss in ahead or astern, as with a conventional fixed blade prop. In astern the aerofoil is working backwards, giving less thrust than in ahead. Some new feathering props have blades that swing right round, so the same leading edge is presented to the water in ahead or astern.

Cut prop drag by 90-95%

Under sail, the drag of folding and feathering props is tiny compared to a standard fixed-blade unit. Feathering props create about 5-10% of a fixed prop’s drag, sometimes less, while folding props have almost zero drag. This gives a significant gain in sailing speed, between half a knot and one knot, with the greatest percentage saving at low speeds.

Inevitably, there are drawbacks. The first is expense: a folding or feathering prop costs between two and six times more than a fixed equivalent. The second issue is complication – the gearing and folding mechanisms are prone to wear and corrosion in the salty and sandy environment, leading to reduced performance, and even loss of blades in extreme circumstances.

The third problem was performance under power. The early folding and feathering props produced less thrust than an equivalent fixed prop, particularly in astern, with dire consequences if the blades fail to deploy when you need to make a crash stop.

Now, the manufacturers claim to have addressed all the issues except cost. They claim the latest generation of their products give as good a performance or better under power, and major gains in speed under sail. We put their claims to the test on two chilly days in February. To our folding and feathering props we added a fixed three-blade prop as a benchmark, and the Axiom prop, a radical new development in fixed propellers, just to see how it compared.

Pitch, diameter, number of blades and handedness all determine a propeller’s performance

To help you understand our test, we will take a quick look at propeller theory and numbers. The four main figures you will see used to describe any prop are diameter, pitch, number of blades, and rotation.

Diameter is twice the distance from the centre of the boss to the tip of the blade. As a rule of thumb, the more powerful your engine, the bigger the diameter you will need.

Pitch is the measure of how far the propeller will advance in one revolution and thus how fast it will push your boat through the water for a given engine rpm (revolutions per minute). To understand pitch, imagine screwing a screw into a block of wood. The angle of the spiral thread governs how far it goes in for each turn. Similarly, the blades of a prop are set at an angle to the boss. The greater the angle, the greater the pitch. However, this is only the theoretical pitch. In practice, as water is not solid, the prop will slip to a degree and not advance so far. The amount of slip is around 30% for the props and speeds we are looking at.

Diameter and pitch are still measured in inches throughout the world – a quirk of history that would delight Henry VIII, and have Napoleon turning in his grave. But pitch can also be measured in degrees, especially relevant with feathering props whose blade angle can be varied.

The number of blades will vary between two, three or four, or even five in some high-speed craft. In practice, more blades will take greater power for a given diameter. For many years sailing boats used two-bladed props as they gave least drag in a boat with a full-length keel and an aperture for the prop, provided it could be locked in the vertical position. Today, most fixed props have three blades. Folding or feathering props have either two for cheapness, or three for higher power.

The hand of the propeller is the direction of rotation in ahead, when you are looking from astern. A right hand prop is one that turns clockwise in ahead.

Blade Area Ratio (BAR), sometimes called Disc Area Ratio, (DAR) is the area of the blades as a percentage of the area of a circle the same diameter as the prop. A prop with a greater BAR will take more power, but have more drag. Figures for sailing boat props are around 60%.

Incidentally, the explanation that a propeller advances just because its blades are angled forward is a convenient way to imagine what is happening, but not strictly correct. The blades of a standard prop are in fact aerofoil in section, like the wing of a plane, and move the boat forwards because as they spin round they develop lift. This lift is caused by a reduction in pressure on the back of the blade (‘back’ being confusingly the blade’s forward face). The faster they go, the greater the reduction in pressure. Once a certain point is reached, the reduction in pressure causes the water next to the blade to vapourise, and form bubbles. This is called cavitation, and limits the amount of power that a given area of blade can cope with. Also, as the bubbles collapse, they erode the metal of the prop, resulting in surface pitting on the back of the blade.

Our test boat was a Beneteau Oceanis 323 with a shaft-mounted fixed three-blade prop

We used a Bénéteau Oceanis 323, kindly leant to us by Sailtime in Lymington. She has a typical fin keel form, but atypically she has a built-in skeg carrying the shaft, rather than the P-bracket or saildrive of most other modern yachts. The skeg protects the shaft and prop from underwater damage, but a downside is increased vibration as the blades of the prop pass through the disturbed waterflow behind the skeg. This is resolved in normal use by fitting a three-bladed prop as standard rather than two, but otherwise did not alter the propulsive element of our test for either two- or three-bladed units.

The engine was a Yanmar YM20, giving 21hp at a maximum 3600rpm. The gearbox ratio is 2.6:1 in ahead, but somewhat confusingly a higher ratio of 3:1 in reverse. This is a very common engine/gearbox combination, so not an unreasonable test. Yanmar says it gives better thrust in astern, but in practice it meant the folding props were forced to use a compromise pitch. Some of the feathering props were able to set a different astern pitch.

We measured the force generated by the engine when running astern

We measured thrust, or ‘bollard pull’, in ahead and astern, throughout the rev range, using a load-cell borrowed from Diverse Yachts, with a remote read-out.

We then measured the side-thrust at full power in astern. This enabled us to predict the prop-walk created when you go into astern. To put this figure into context, the thrust produced by the worst prop in our test is the same as a 3hp outboard mounted on the transom, driving at right-angles at full throttle. No wonder so many yachts veer off to one side!

On the water, we measured speed through the rev range to maximum. We then carried out a crash stop from 6 knots. We recorded the time it took to bring the boat to rest at full throttle from the moment we engaged reverse gear.

To put these times into context, the distance the boat would travel before stopping would be 12m (39ft) with the best prop tested, but 17.4m (57ft) with the worst.

To measure the drag of all 18 propellers precisely enough to compare them with one another, making allowances for different yacht hull forms, we would have had to build a sophisticated testing rig, hire a team of scientists and spend several days in a research laboratory with a very large towing tank. Our objective was just to demonstrate the difference in drag caused by different types of propeller.

We tested the drag of three types of propeller using this test rig

We fitted a fixed prop, then a folding one, then a feathering one, to an outboard motor leg mounted on the transom of a lightweight 14ft skiff. We then towed the skiff at speeds up to 7 knots, and measured the difference in drag. We don’t claim this gave us the last degree of accuracy, but it was sufficient to compare with published drag figures. We then compared this drag to the hull-only drag of the Océanis 323 – a typical 10m cruising yacht.

A question of some gravity, Mr Newton

To keep things simple, we have presented our drag and thrust figures in kilograms (kg). Strictly speaking, thrust is a force and should be measured in Newtons – 1kg is multiplied by the acceleration due to gravity to give a figure of 9.81N. On another planet, with different gravity, our units would be wrong, but until we hear they are holding regattas on the canals of Mars, we will rest our case.

The results

Featherstream three-blade

Made in England at the time of writing (2009), this is a three-blade feathering unit with a bronze boss, and stainless steel blades. The pitch of the blades can be adjusted externally, and can be different for ahead and astern. The blades swivel 180º to present the same leading edge in ahead and astern. As a result, it performed well in astern: second best for bollard pull and third for stopping distance. However, occasionally it would not open in astern, and you had to learn to snap the throttle hard to get it to deploy.

Max Prop three-blade

Designed by Massimiliano Bianchi in 1976, the Max Prop was one of the first of the new generation of props. Boss and blades are bronze, and the pitch can be set as you assemble it, or by the factory if you want a different astern pitch. The blades swivel 180º to present the same leading edge in ahead and astern. It gave the best astern thrust, and was in the middle of the pack for stopping distance. It never missed a beat going into astern.

Max Prop two-blade

A two-blade version of the Max prop. As expected, it gave some vibration on our test boat, but this would not occur on a yacht with a P-bracket or saildrive. Mid-range performance for astern thrust and stopping distance.

Kiwi Prop three-blade

Designed in New Zealand in 2000, this is only available as a three-blade unit. The boss is stainless steel, and the blades are glass-reinforced Zytel plastic. Each blade has two different aerofoil sections, as you move out from the boss. It has no internal gears, so each blade feathers independently according to the waterflow over it. The blades do not swing completely round in reverse, so the trailing edge becomes the leading edge. It was one of the simplest to fit – just slide it on and tighten the nut. Mid-range for astern thrust and stopping distance, but the lowest top speed. It also went easily into astern.

Brunton’s Autoprop

Brunton’s Autoprop marked a completely different approach to feathering props when it was brought out in 1987. The three blades are linked together, going from fully feathered while sailing, or in neutral, to fully twisted under power. The difference is that when you go into gear, the amount they rotate depends on engine speed and loading. Thus the ahead or astern pitch varies according to engine rpm, which, Brunton claims, improves performance and fuel economy, with reduced rpm for a given cruising speed. We can confirm the latter: our tests show the Autoprop achieved 6 knots at 2,100rpm, compared to 2,500rpm for our standard prop and most of the others on test. However, previous drag tests have shown that this is achieved at the expense of slightly more drag than other feathering props, though still 80% less than a fixed prop. Bollard pulls were on the low side, but it still achieved near the maximum top speed, with mid-range stopping distance.

Autostream three-blade

From Australia comes the Autostream, a three-bladed feathering unit that has been in production for 20 years. Construction is all-stainless steel, with the blades swivelling 180º to give the same leading edge in astern as ahead. Separate ahead and astern pitch can be adjusted by the owner without dismantling the prop. It has been designed to stay feathered at speeds up to 25 knots, helped by extra blade area aft, making it suitable for fast multihulls. On test, it gave the fastest stopping time of all the folding or feathering units, plus significantly lower side-thrust than the rest, while still maintaining good ahead speed.

Variprofile three-blade

This is a three-blade feathering prop, made in Germany. The blades swivel 180º to give the same leading edge in astern, and the pitch can be set differently for ahead and astern. Usually, this is set in advance for the customer, but can be altered on site. Blades and boss are bronze, with stainless pins, and an anode aft of the nut. Ahead thrust was low, but stopping distance was good.

Flexofold three-blade

Made in Denmark at the time of writing (2009), the Flexofold is an all-bronze folding unit, with stainless steel pins, and the anode cleverly enclosed by the blades. On test, it gave the equal highest forward thrust of all props, and highest top speed. It also had one of the lowest side-thrusts. Astern performance was the best of the folding props. At a cruising speed of 6 knots, the engine was turning at 2,300rpm, compared to the 2,500rpm of our standard fixed prop and most of the others on test.

Flexofold two-blade

A two-blade version of the Flexofold, its performance was only slightly down on the three-blade, and in fact better for astern thrust. Again, it had some vibration due to the skeg. A racing two-blade version is also available.

Gori three-blade

Another of the earliest folding designs, the Gori has been made in Denmark since 1975, in two and three-blade versions, but the company only recommended the three-blade for this boat. They also make a racing two-blade version, with reduced drag. The blades have a three-way gearing system for opening and closing. Boss and blades are bronze, with stainless steel pins. A speciality is its overdrive feature, which sets the blades in a coarser pitch if you open the throttle gradually while the boat has forward way on, which allows you to cruise or motorsail at lower rpm for more comfort. Performance ahead and astern were towards the bottom of our list, with the longest stopping distance, but the prop-walk was third best.

Slipstream three-blade

From the same Australian company as the Autostream comes the Slipstream folding prop. Again the boss and blades are stainless steel, which gives greater strength, allows thinner section blades, and removes the need for an anode. The bearings are bronze bushes, while the blade gears are bevelled, with two rows each, claimed to better chew up any barnacles that might chose to grow on them. Polyethylene side thrust washers further improve the opening action. On test it performed in the middle of the folding props, though with comfortable low cruising revs of 2,250rpm at 6 knots.

Slipstream two-blade

Similar in design to the three-blade version, though with slightly worse astern figures, but it still made 6 knots at a low cruising rpm of 2,350.

Varifold two-blade

Made in the UK, this is mid-way between a racing and cruising prop, with the blades closing tightly for low drag, but still having enough shape to give good motoring performance. As a result of its close fit, you have to give the engine a burst of throttle to get the blades to open initially. It has a bronze boss and blades, and stainless steel pins. It gave equal highest top speed, but was near the bottom of astern performance.

Axiom three-blade

Axiom fixed three-blade

The Axiom is the joker in our pack. It is not a folding propeller, but it does have a revolutionary blade profile and section, if you will pardon the pun, and has never been tested on a yacht before, so we just had to put it into our trials to see how it compared. As the photograph shows, the blade profile is rectangular, while the blade section is almost S-shaped, and symmetrical in ahead and astern, with no twist. Its designers claim it gives greater thrust and stopping power, together with lower wash. So how did it stand up? Well the charts show the story, with its stopping time nearly a second better than any other model, and its side thrust again the lowest by far. However this was at the expense of lower top speed, which suggests some more tweaking is needed, but it is still one to watch.

Drag curves

Drag v speed

In the graph above, you can see that at 5 knots, a fixed three-blade prop with its shaft locked creates almost half as much drag as the entire hull. The drag can be halved by allowing the prop to spin, but the gearbox may suffer. By contrast, the drag of a feathering prop is negligible, and the drag of a folding prop is too small to plot on a graph of this scale.

The hull resistance curve for the Océanis 323 was calculated for YM by the Wolfson Unit, at the University of Southampton, using data from the Delft University Systematic Series. The propeller drag curves are based on data from SSPA Maritime Consulting, using Volvo S-drives. This data were verified by YM’s on-the-water drag test.

All but three of the propellers on test produced less prop walk than the standard fixed prop. The fixed Axiom and feathering Autostream were the best performers, but nearly all the folding props fared better than the rest of the feathering propellers.

Maximum speed

There was more than half a knot of difference between the best-performing props and the worst. Four folding propellers and one feathering prop managed to prove the claim of better performance than a standard fixed prop, but nine of them fell slightly short.

Interestingly, some of the best performers were two-bladed props, which are widely assumed to perform worse than three-blade versions.

Bollard pull ahead

The fastest props are generally also the most powerful in ahead, and most of the slower ones are among the least powerful. However, only one unit – the three-bladed Flexofold – generated a greater bollard pull than the standard fixed prop. The most powerful props produce almost a third more thrust than some of their rivals.

Bollard pull astern

Three propellers produced a more powerful bollard pull than the standard fixed prop in astern: two folding units and the newly designed Axiom. Nearly all the feathering props performed better in astern than the folding ones – some by a very wide margin. There’s a huge difference between the best and worst-performing props – the three-blade Max Prop has almost twice the bollard pull of the two-blade Varifold.

Stopping time

The new-concept Axiom prop excelled in this test, but nearly all the feathering props were better at bringing the boat to a standstill than the standard prop. The folding props were less effective and some of them were less than 100% reliable when called upon to perform an emergency stop. The difference between the best and worst stoppers was about 3½ seconds. It may not sound like much, but in a crunch, it could make all the difference.

If you want to add up to a knot to your boat speed, then fitting a folding or feathering propeller is a must, not just for racing boats. And as our test demonstrates, you can usually still retain the handling and performance under power that you had with a standard fixed-blade prop. In fact, often you’ll get better performance.

Five of the tested props gave more speed than the standard prop, with four of them being folding models, and both Flexofolds coming out top. And even though it was only 0.15 knots better, when you look at the hull resistance curve this is a considerable improvement. On the other hand, with astern performance, in general it was the feathering props that came out best, with better bollard pull than the standard, and better stopping times, and the Autostream coming out top. The folding props were generally not as good as the standard, though in the main only by no more than 10%.

But it was the prop-walk figures that proved the most interesting. Ten of our test units gave less prop-walk, with generally the folders coming out best, but the top units being the Axiom and Autostream, with 30% less side-thrust than the standard fixed three-blade, a considerable advantage when you have to stop suddenly or back-up in a marina.

In terms of resistance, our test shows that letting your fixed-blade prop spin, if the gearbox manufacturer will allow it, halves the drag. But to get the real improvement, fitting a folding prop will give at least 95% less drag than a locked, fixed propeller, while a feathering unit will give at least 92% of the drag – still an enormous saving.

But these benefits do have a price, literally on your wallet. A 16in fixed three-blade propeller will cost around £300 (2009 prices in UK). But the cheapest two-blade folding prop will be at least double this price, with most of them between £600-900. For a three-bladed folding unit expect to pay between £1,200 and £1,600. Feathering props are even more expensive, starting at around £1,200 for a two-blade model, rising to £2,100 for the most expensive three-blade version.

Because of the wide variation in cost, performance and specifications of the all the units tested, we have not felt it appropriate to recommend a best buy. The tables and curves give you the information you need at a glance, allowing you to make your own decisions as to which is best for you and your boat.

Some are easy to fit, others difficult. Professional installation is advised for such an important – and expensive – bit of kit

Some of the props on test are very simple to install, others are very complicated. However, while they all have instructions for DIY fitting, unless you’re very confident in your own skills, a piece of equipment as vital as a propeller ought to be professionally installed, both for safety and peace of mind. For our test, we had every prop fitted by the manufacturer’s representative, so there was no question about the installation, and they also observed all our measurements.

Bronze has been the material of choice for propellers almost since they were invented. Strong, resistant to salt-water corrosion, it is also easy to cast, with a low melting point, as our ancestors found out 4,000 years ago. Stainless steel has been making an appearance recently. Even stronger, it allows thinner and so more efficient blades. It is even more corrosion resistant, and also harder, so less vulnerable to impact damage. However, it has a much higher melting point, so it is more difficult and expensive to cast and machine.

Maintenance

A folding or feathering prop will need more maintenance than a fixed prop

Whatever prop you have, it should be checked every time the boat is lifted, for wear, corrosion and movement. Folding and feathering props do require more maintenance than fixed ones. Some bosses are packed with grease, which should be repacked annually. Some have nylon shims or bearings, which should be checked, especially in silted waters. Most have an anode, which should be checked and replaced if necessary.

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Many models of Max-Prop automatic feathering propellers available so you'll be sure to find the one that fits your needs perfectly.

One of the most important features of the Max-Prop is that it feathers automatically with the forward momentum of the boat. Once feathered, it provides the least possible drag (similar to a folding prop) improving the vessel's sailing speed by an average of 15% above a conventional fixed blade propeller.

In forward: the Max-Prop will offer 96% of the efficiency of a fixed blade propeller of the same diameter and pitch. The 4% loss in power can usually be eliminated by precisely matching the pitch of the Max-Prop to fit the boat engine combination. In reverse: the Max-Prop provides 80% more power than a comparable fixed blade propeller. The Max-Prop utilizes the same leading edge in forward as it does in reverse giving the propeller the same efficiency in both directions, whereas on a fixed blade propeller in reverse the trailing edge becomes the leading edge therefore reducing its power. .

RELIABILITY

The Max-Prop uses a "differential" type design so that the blades cannot fail to open in forward or reverse. This positive system eliminates the problem associated with a folding propeller and its use of centrifugal force to open the blades. In a recent survey of Seven Sea Cruising Association readers the Max-Prop received a perfect rating on no failures ( one of only two products to receive such high praise). About 32,000 Max-Prop are in operation today!

VERSATILITY

The pitch setting on all Max-Prop models can be adjusted. Changing the pitch is very simple; it is done by changing the setting of the gear inside the propeller with the Classic (usually upon a haul out). Or by removing a bolt and replacing with one of a different length with the Easy and Whisper. The ability to adjust the pitch will help achieve the maximum efficiency from the engine without having to purchase a new propeller.

Max-Prop ADVANTAGES

A Max-Prop feathers to a low drag shape. Compared to a folding propeller, the extra wetted surface of the Max-Prop blades is offset by the reduction of projected area: A.

The torque of the prop shaft acting on the "differential" type design will open the blades in unison to the preset pitch at any throttle setting. This will provide maximum efficiency (96% of same size fixed prop) plus eliminates the vibration problems of a folding prop. .

As in forward, the torque of the shaft will rotate the blades, 180 degrees in less than 3/4 of a shaft rotation, presenting the same leading edge and pitch in reverse. This provides better directional control and 80% greater power than a comparable fixed blade propeller.

Want to learn more about our Max-Prop products or how to adjust or install a Max-Prop ? Check out our Youtube channel for all of our videos.

* Only when using Seaview Modular Top Plate #ADAR1DMLTB.

Feathering Propellers: Overview, Benefits and Cost vs. Benefit Considerations

What are feathering propellers.

Feathering propellers for sailboats, also known as feathering or folding propellers, are a special type of propeller designed to improve the performance and efficiency of sailboats. Unlike traditional fixed propellers, feathering propellers allow the blades to rotate in such a way that they can be adjusted to reduce drag when the boat is under sail. This allows the boat to move more efficiently through the water, resulting in better speed and fuel economy.

Feathering propellers work by adjusting the angle of the blades relative to the water flow. When the boat is under sail, the blades can be positioned parallel to the water flow, reducing drag and allowing the boat to move more efficiently. When the boat is under power, the blades can be adjusted to a more traditional propeller position, providing maximum thrust.

The use of feathering propellers on sailboats is not a new concept, but it has become increasingly popular in recent years as sailors look for ways to improve the performance and efficiency of their vessels. With the right selection and setup, feathering propellers can make a significant difference in the speed and fuel economy of a sailboat.

how feathering propellers improve sailboat performance and efficiency

Feathering propellers can greatly improve the performance and efficiency of sailboats in a number of ways. Firstly, the ability to reduce drag when the boat is under sail allows for faster sailing speeds. This is because the feathering propeller’s blades turn in the direction of the water flow, which reduces resistance and allows the boat to travel faster.

Secondly, feathering propellers can also improve the maneuverability of a sailboat. This is because the blades can be adjusted to provide thrust in both forward and reverse, which makes it easier to turn and maneuver the boat, avoiding the dreaded “prop walk” typically found when reversing a sailboat. This can be especially useful in tight spaces or when navigating in shallow waters.

Overall, feathering propellers can be a great addition to any sailboat, providing improved performance, efficiency, maneuverability and safety. With the right selection, feathering propellers can make sailing more enjoyable and efficient.

installation, pitch adjustment and maintenance benefits

There are a few additional benefits of feathering propellers that can help justify the additional costs:

• Installation: Feathering propellers can be easily installed or pulled in just a few minutes underwater. This can avoid expensive boat hauling fees when your propeller needs maintenance or to be replaced.
• Adjusting Pitch: Adjusting propeller pitch can be done while the propeller is installed. For example, our EWOL and J-Prop feathering propellers can have their pitch mico-adjusted underwater in less than 20 seconds. This can be an expensive process for fixed blade propellers and propeller pitch is very important to the longevity of your propulsion engine as well. Your engine needs a proper load to ensure it is running in the proper rpm range. Propeller size and pitch make up an important part of this equation.
• Reduced Wear: Lastly, there are benefits such as enclosed gear drives that avoid fouling and the feathering propeller eliminates vibrations and gear box wear and tear because the propeller isn’t turning while under sail.

ARe feathering propellers worth the costs?

Value, like other things, is in the eye of the beholder! Whether or not a feathering propeller is worth the cost to you depends on a number of factors, including the type of sailing you’ll be doing, the size of your boat, and your budget. In general, feathering propellers can provide significant benefits in terms of performance, efficiency and reduced maintenance costs over time, which can make them well worth the cost for some sailors. The more you sail and the longer you plan to own your boat then the more value you will derive from your feathering propeller.

If you are interested in learning more about feathering propellers and the suitability for your vessel, give us a call and we can review various options, or you can review our products at the link below.

Beta Marine’s Feathering Propellers

The only true feathering sailboat propeller

Autoprop Feathering Sailboat Propellers

Autoprop is a sailboat propeller which varies its pitch depending on the operating conditions, to maintain maximum efficiency at all times. The propeller self-pitches based on the hydrodynamic flow at the propeller. It has a higher efficiency over a wider range of rpm settings than any other type of sailboat propeller, so it produces higher speeds throughout your engine’s speed range, allowing lower engine rpm’s, giving greater cruising ranges, fuel economy and quieter cruising. The blades automatically adjust their pitch to match the engine torque to the varying load conditions.

The feathered image on the right shows how, when sailing, Autoprop reduces drag by up to 85% compared with a three blade fixed propeller; with the two blade propeller the reduction can be even greater. This drag reduction can equate to as much as one additional knot in sailing speed.

Motor Sailing

Autoprop automatically varies its pitch depending on engine, wind or sea conditions. The result is maximum efficiency whatever the conditions, with increased sailing speeds at dramatically lower engine rpm giving lower fuel consumption and emissions.

Autoprops unusual blades maximize the thrust delivered whatever rpm the engine is running at. Conventional propellers are designed to provide maximum thrust at the engines maximum output.  Autoprops self feathering provides maximum thrust at all, not a single rpm range.

Maneuvering

In reverse the Autoprop blades swing through 180 degrees and present exactly the same blade shape as they do ahead. The result, the same excellent thrust, with greater stopping power and less prop walk.

Bad Weather

In high winds and choppy seas sailboats struggle to make way. Autoprop allows the engine to to run to a higher maximum rpm delivering more power than any competitor to get you home safely.

Autoprop can use the full power of the engine for towing, or emergencies. The self pitching blades allow full thrust to be developed for extended periods of time without causing overheating or risk to the propulsion system.

Why Autoprop?

All sailboat propellers with the exception of Autoprop are designed to work at one pitch setting.  At this point, normally the maximum engine rpm and hull speed, the sailboat propeller is at peak efficiency.   Do you run your sailboat at full throttle?

Once rpm is reduced to cruising speed, the pitch for the propeller is still set for the maximum value forcing the propeller to work harder to maintain speed; this causes an increase in fuel burn and also an increase in engine emissions. This is how all sailboat propellers work regardless of manufacturer.

Tests on all 4 of the sailboat propeller types found that at 2000 rpm a feathering sailboat propeller was able to propel a test boat at 5.4 knots, but when the same sailboat was fitted with an Autoprop feathering propeller, the boat was able to achieve 6.9 knots for the same rpm and hence fuel consumption.

Autoprop is different.  It balances the rotational forces of the propeller with the forward speed of the boat to automatically set the correct pitch for the correct seaway at every rpm. This will result in cruising speed increases of up to 1 knot or more compared to every other sailboat propeller. There is no other sailboat propeller on the market that does this and this makes Autoprop the perfect motor sailing propeller. Most sailers see typical fuel consumption reduced by 25%, allowing them to sail further for longer.

But Autoprop is not only great under power, once the engine is shutdown, Autoprop can be feathered and it becomes a low drag sailing propeller – the best of both worlds!

Only fully automatic self-pitching propeller on the market

Autoprop has a maximum mid range efficiency of 70% which is higher than all other sailboat propellers – Fixed, Folding or Feathering

Blades are custom airfoil sections and not symmetric sections like all other feathering propellers. This gives significantly improved performance and noise characteristics under power compared to all other feathering propellers

In reverse maneuvers, the blades rotate and give 100% thrust. This gives greater stopping power, greater control, improved handling, almost no prop walk

The Autoprop Range

Autoprop is available in a wide range of sizes and configurations to suit many styles of sailing and sailboats. Typical diameters are from 13″ to 39″ and engine ratings from 10 HP to 350 HP.

Autoprop Service & Support

Fitting, maintaining and servicing an Autoprop could not be easier with the help and guidance of King Propulsion of Virginia Beach, VA.

When you receive your Autoprop it comes fully assembled and pre-greased. Installation on your sailboat is as simple as bolting it on the propeller shaft / saildrive leg, tightening the lock screw and fit the anode. This operation is best completed on the hard or at a short haul. ​ Maintenance is just as simple. Once your sailboat is hauled out and on the hard, ball bearing type Autoprops need a simple cleaning and roller bearing type Autoprops need to be re-greased before winterizing. At this time any eroded anodes are changed and the blades are cleaned and painted in accordance with the maintenance schedule.

Once the blade bearings reach the end of their service life, a service kit is available for each and every Autoprop model along with the necessary tools to complete the service. These kits contain the parts needed to rebuild your propeller back to factory new. As Autoprop doesn’t use gears to pitch the blades like most of our competitors, all the wearing parts are replaceable, vastly extending the life of the propeller. This is a straight forward process that should take a couple of hours per blade. Extensive how too videos are available as well as phone support from our office (East Coast Time), should things go a little pear shaped!

Click the download archive link given below to download the fitting and maintenance instructions for any of the Autoprop models. The files are in PDF format for easy viewing or downloading. Parts to complete any maintenance or repairs can easily be purchased from our online store and ship from Virginia Beach, VA.

Autoprop Sizing & Quote

Find out how Autoprop sailboat propellers can benefit your sailboat by requesting a hassle free no obligation quote. Simply enter the details of your sailboat such as boat type , engine, gearbox ratio and so on in our online web form and we will conduct a power prediction for your vessel to size the right propeller for you. We have currently installed nearly 11,000 Autoprop feathering propellers and counting.

NEXT GENERATION FEATHERING PROPELLER

GOODWILL PROP

INTRODUCING THE RE-INVENTION OF THE FEATHERING PROPELLER .

For the sailor, faster sailing, best performance under sail at high speeds.

Our patented fully automated return mechanism returns a propeller to the correct position without complicated feathering maneuvers in less than a quarter of a shaft turn, ahead as well as astern.

Outstanding maneuverability

This provides the fastest control response to date for a feathering propeller giving greater safety and improved handling in close quarters.

Easy pitch adjustment

Our patented worm drive mechanism gives very accurate pitch adjustment of the propeller with increments as small as 0.1 degree.

FOR THE BOAT

Less damage & maintenance, fluid & reliable operation.

Our patented gear-free mechanism reduces maintenance and eliminates the need to rebuild the propeller due to wear in the gears.

Less damage to transmission

The built-in shock absorber protects the propeller and drive train from abrupt maneuvering and the automated return mechanism eliminates the need to install a shaft brake.

High strength materials

Built with advanced materials including nickel-aluminium bronze, stainless steel and titanium for reliability, wear and corrosion resistance - all protected by a long lasting zinc anode.​

CRAFTSMANSHIP

Precise engineering + italian style.

​Each propeller is hand made in our workshop in Italy with meticulous attention to detail and the greatest care. It bears within its design the signs of our efforts and tells the story of our devotion through its impressive performance and durability.

ENVIRONMENTAL

Plastic-free packaging & reduced pollution.

​Starting right from it's journey in eco friendly plastic-free packaging through it's entire life, we have taken every step to minimise our impact on the environment. Our innovative design uses 8 rubber gaskets in each propeller to prevent grease escaping into the ocean, causing less environmental pollution than traditional feathering propellers.

INNOVATIVE FEATURES

New patented gearless mechanism, fully-automated feathering, fast control  response, easy pitch adjustment, high-tech materials.

SPECIFICATION

Shaft sizes.

ISO: 25-30 / SAE:1”-1⅛” / Sail Drive

7 - 9.5 kg

Grease gaskets

N°8 Dinamic X-Rings

Spring-loaded

Stainless Steel Spring

Minimum Pre-load 270 N

356 mm (14”) to 457 mm (18”)

Pitch regulation

Manual: from 12° to 30°blade angle

(1 screw rotation = 0,53° blade angle variation)

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Choosing the Proper Sailboat Prop

• By David Schmidt
• Updated: July 21, 2021

As sailors, it’s romantic to think that our locomotion comes from the wind, but most skippers, when pressed, admit to motoring a fair portion of the time. Like it or not, your boat’s propeller is a key element of the propulsion system, and just as there are myriad considerations involved when ordering sails, decisions abound when selecting the prop that best suits your wallet and sailing plans.

Fixed-Blade Options

As the moniker implies, fixed-blade propellers are typically cast out of an alloy such as manganese bronze or nickel, bronze and aluminum. Individual propeller blades stem from a central hub, which in turn attaches to the sailboat’s prop shaft or saildrive. Depending on the manufacturer, these blades typically are pitched in a way that propels the boat forward or backward when the transmission is engaged. The term “pitch” refers to how far forward or reverse a propeller will theoretically travel through a solid material (picture a screw twisting into a wood block). For example, a prop with a 12-inch pitch will theoretically move through 1 foot of solid material with each full rotation.

Sailors have choices available when buying a fixed-blade propeller, with the biggest variables being the ­diameter, the number of propeller blades, and the pitch. Just as sailboats create “dirty air” that spills off their sails, propeller blades push water against the hull, which then reverberates back (call this “dirty water”). When the transmission is in forward, this dirty water is sent back toward the rudder, which can influence steering. An important rule of thumb for all propeller designs and types is to ensure that the propeller has a tip clearance (the amount of space between a blade’s tip and the hull when the blade is in the 12 o’clock position) that’s at least 10 percent of the length of the prop blade (hub to tip). If you don’t have enough tip clearance, the next step is to spec a smaller-diameter propeller with an extra blade. Fixed props are available with two, three or four blades.

While this can be an easy fix, additional blades create additional drag when the boat is sailing. Because of this, sailors who opt for a fixed-blade prop are typically best served choosing a screw with the fewest number of blades that can properly fit their boat and their engine (see “Choosing Screws,” right). That said, additional blades equate to more power when motoring into a stiff headwind, current or big seas. Additional propeller blades can also accommodate a more powerful engine at a given diameter. These latter points are important if you’re planning on cruising unfamiliar waters and might find yourself negotiating a lee shore under power.

While fixed-blade ­propellers are strong, simple, relatively inexpensive, and ­easier to have repaired in remote locales, they do affect sailing performance. Moreover, they’re more likely to foul a lobster pot or other fishing gear than a folding prop when the boat is sailing. If you care about sailing performance, especially in the light stuff, or if you’re planning a long-distance cruise, purchasing a folding or feathering prop is a wise investment. But if you’re seeking maximum power or punch for your buck, and you sail on breezy waters such as San Francisco Bay, where extra drag isn’t a huge concern, a fixed-blade prop could be the way to go.

Folding Propellers

Folding propellers employ a series of gears (situated around the prop’s central hub and on the inboard end of each prop blade) and centrifugal force to open when the engine’s transmission is engaged. The slipstream action of the passing water acts to fold them closed when sailing, and their gear mechanisms hold the blades in their closed position even in light airs. As with fixed-blade props, sailors can choose between models that feature two, three or four blades. Unlike fixed-blade props, however, folding propellers create far less drag when the boat is sailing.

“For the same diameter and number of blades, folding propellers have 85 to 100 percent less drag than a fixed prop, depending on the fixed propeller’s blade area and the folding propeller’s make and model,” says Geoff Prior, owner of AB Marine, the Newport, Rhode Island-based importer and distributor for Gori folding props and AutoProp, Variprofile, and Variprop feathering propellers. “Geared folding propellers stay closed or folded when the boat is sailing, so a blade cannot drop down to be exposed to the water flow, and does not catch lines and weeds like fixed and feathering propellers can.”

Others agree. “Most sailboats will gain 0.5 to even 1 knot of speed by using a low-drag folding propeller,” says Keld Willberg, Flexofold’s general manager. “Many boat owners don’t look just at the speed gains, but also the ability to sail in very light wind.” Also, he says, when tacking, a boat that’s equipped with a low-drag prop won’t lose as much momentum.

This latter point is critical to anyone who sails in places with typically light breeze. “The folding propeller’s drag reduction and increased sailing speeds produce less turbulence over the rudder, enabling you to point higher, steer easier and more precisely, and tack and jibe the boat easier,” Prior says. “The biggest speed difference is in light or medium air and with clean water flow over the rudder—the boat is a lot more responsive, especially when fine sailing on the wind.”

One important consideration when selecting a folding prop is ensuring that your boat can physically accommodate the length of the prop when it’s folded. This is especially important on full-keel boats that have an aperture between the keel and rudder. For anyone who cruises with a saildrive(s), Prior advises that saildrive propellers must be approved for use by the saildrive’s manufacturer to ensure that the prop is electrically isolated from the saildrive’s leg and shaft; also the prop’s hub must incorporate a rubberized bushing to absorb shock and inertia, as well as an easily changed and ­streamlined anode.

As with all props, ­selecting the diameter, number of blades, and pitch of the propeller are all key decisions. “Diameter is the single most critical factor in determining the amount of power that a propeller absorbs and transmits into the water,” Prior says. “It’s the most important single factor in determining the amount of thrust delivered. The larger the diameter, the greater the efficiency. A small increase in diameter dramatically increases thrust and torque load on the engine and shaft.”

Blade count is also critical, but Willberg cautions that it’s overly simplistic to think that additional blades equate to additional power (see “Calling the Pitch,” right). “What ­matters is to get the right combination of blade area and pitch for the engine and gear box,” he says. “On flat water, a two-blade propeller can be just as efficient or even slightly better than a three-blade. However, when motoring against wind and waves, and when maneuvering, you get more power from a ­three-blade prop.”

Blade shape also matters. “Propellers with flat, planar blades are like a paddle,” Prior says. “The flat shape is not ­efficient at producing thrust because a flat blade is overloaded at the tip and underloaded at the blade base, whereas a fully shaped airfoil blade shape has a constant loading over its whole surface.” Much like fixed-blade props, most folding propellers employ an efficient blade shape, while feathering props use flatter and more ­planar-shaped blades.

One drawback of most (but not all) folding props emerges when the transmission is put into reverse. “In reverse, the suction side is on the back or aft side of a blade, and with the typical folding propeller design, the blades are trying to close in reverse, giving low thrust and lots of prop walk,” says Prior, who added that Gori’s three-blade prop presents identical leading-blade edges in both forward and reverse, negating this issue. Willberg advises that folding props require slightly different operation than fixed-blade or feathering props to ensure that they stay open. “For more stopping and reverse power, it’s just a matter of giving more revs on the throttle,” he says.

RELATED: Understanding Your Sailboat Propellers

As with all props, folding propellers must be kept clean of marine growth, and anodes must be regularly changed to ensure cathodic protection. “One millimeter of growth on a blade and your propeller loses approximately 12 percent efficiency,” Prior says, adding that this applies to any make, model or design. And, he notes, “folding propellers are water-lubricated, so they do not need to be greased.”

The final consideration is cost. Folding props are roughly four to six times more expensive than a fixed-blade propeller for a given diameter and blade count. While this is a big difference, the gains are huge, and—for bluewater cruisers—can translate to ­significantly faster passage times (potentially measured in days) and happier crews.

Feathering Propellers

As do folding propellers, feathering props greatly reduce drag when the boat is sailing; however, the way that they achieve this gain is significantly different. Moreover, the physics behind how the prop transitions from its sailing mode to motoring mode is also different.

Feathering props are available with two-, three-, four- and five-blade configurations. A central hub attaches to the prop shaft or a saildrive, and it features a series of internal beveled gears. Geared propeller blades attach to the hub and rotate through 180 degrees, depending on if the transmission is in forward or reverse (more on this later); this articulation is governed by machined stops inside the hub that prevent the blades from overrotating. When the transmission is engaged, the blades present their broad sides to the slipstream, but when the boat is under sail, the blades rotate 90 degrees to align with the flow of the water.

“Feathering props work off torque from the shaft or saildrive,” says Fred Hutchison, at PYI, which distributes Max-Prop feathering propellers. Because feathering props use torque—not centrifugal force—to open, it’s “instantaneous,” says Hutchison, who points to this as the design’s biggest advantage. “It takes a feathering prop only three-quarters of a turn to go from full forward to full reverse. In that time, the blades rotate 180 degrees, and it doesn’t generate much shock load.”

Prior adds, “In the sailing position, the water flow turns the blades to the feathered position when the engine is off for vastly reduced drag.” He estimates that this drag reduction is approximately 85 percent compared with fixed-blade props.

As previously mentioned, feathering-prop blades rotate through 180 degrees, which is a big advantage when operating in reverse compared with most folding props. “A feathering propeller gives reverse thrust with the same efficiency as in forward, as the leading blade edge in forward is turned 180 degrees, and without prop walk,” Prior says.

Another advantage of feathering props for boats with full keels or with tightly spaced skegs or rudders is that they “can fit in a small aperture as they have shorter overall lengths compared to folding propellers, which have a greater length when folded,” Prior says. “If there is a diameter constraint, the feathering prop can easily be designed and built with a higher pitch to make up for the loss of diameter and blade area.”

Most feathering props are machined out of a nickel, bronze and aluminum alloy, which, Hutchison says, makes them easy to repair. Unlike fixed or folding ­propellers, feathering propellers employ flat-shaped blades to reduce drag when the boat is sailing. “Feathering propeller blades are foiled and aren’t as efficient as the helical twist found on most fixed-blade or folding props,” Hutchison says, adding that manufacturers compensate for this less-efficient shape by increasing each blade’s surface area. “Blade surface area and shape make a big difference in how efficient it is,” he says. “No low-drag prop will be as efficient under power as a fixed-blade propeller.”

Lobster pots and fishing nets are common concerns when operating under auxiliary power, and feathering props are not snag-proof. “When motoring, feathering props are the same as fixed-blade and folding propellers,” Hutchison advises. “But when sailing, a folding propeller has less of a chance of catching a pot or fishing net than a fixed-blade or feathering propeller.” This is a consideration for anyone who cruises extensively in, say, Maine or in heavily fished waters off the West Coast.

As with all propellers, feathering props require basic care and maintenance to ensure their efficiency and the engine’s longevity. This starts with a properly spec’d and regularly refreshed anode, and the prop blades must be kept clean.

Unlike folding props, which typically use exposed self-­lubricating gears, the internal gears of feathering propellers need to be greased annually. While this adds an item to an owner’s yearly to-do list, Hutchison says that this can be tackled by a diver.

Finally, while feathering props are a great upgrade, they don’t come cheap. “Feathering props are more expensive than folding props,” says Hutchison, who ­advises that a feathering prop is roughly 10 to 15 percent more ­expensive than a folding prop with the same blade count and a ­comparable diameter. “This is primarily because of ­machining costs,” he says.

David Schmidt is CW ’s electronics editor and also writes about topics ranging from sailing gear to environmental issues from his home in Bellingham, Washington.

Choosing Screws

Choosing the right propeller is complex, but the most important variables for selecting the correct prop are your boat’s make, model, LOA and displacement, the engine’s horsepower rating and its maximum rpm, as well as the transmission’s reduction ratio. While most of this information is easily ascertained, determining the reduction ratio can be challenging. But, Prior says, “the best method to get the actual ratio is to use your cellphone camera and take a photo of the plate on the transmission,” adding that this beats hanging upside down and trying to read this information using a mirror and flashlight. For the DIYer, online calculators exist that can help crunch the numbers. “After that, it gets into the art,” Hutchison says. His advice: Ask an expert.

Calling the Pitch

Unlike fixed-blade propellers, feathering and folding propellers are often designed so that the pitch can be adjusted, perchance it doesn’t perfectly match your vessel, engine and transmission right out of the box. Depending on the prop, this adjustment is typically made by changing a screw(s) or swapping out the prop blades. These adjustments can usually be done by a diver while the boat is in the water. Some general rules of thumb as to when to change the pitch involve engine rpm: If the prop doesn’t meet the engine’s ideal rpm, the blade’s angle needs to be reduced; conversely, if the prop is exceeding the engine’s rpm metrics, the blade’s angle of attack needs to be increased. As a cautionary note, overpitching a propeller can cause the engine to overheat, and it can also lead to injector-choking problems and create excessive internal engine pressure, so be sure to stay within the engine ­manufacturer’s lines.

Vendor Information

EWOL: ewoltech.com , 410-317-8104; from $2,120

Flexofold: flexofold.com , 781-797-0809; from $980

GORI: gori-propeller.com , 401-847-7960; from $650

J Prop: betamarinenc.com , 252-249-2473; from $2,500

Kiwiprop: kiwiprops.co.nz , 877-549-4872; from $1,350

Max-Prop: pyiinc.com , 425-355-3669; from $1,900

Michigan Wheel: ­ miwheel.com , 800-369-4335; from $550

Variprofile: spw-gmbh.de , 401-847-7960; from $800

Variprop: spw-gmbh.de , 401-847-7960; from $1,200

Volvo: volvopenta.us , 800-522-1959; call for pricing

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Folding Propellers vs. Feathering Propellers

Unlike a fixed propeller, which is known for creating a substantial amount of drag when sailing, fitting a folding propeller or feathering propeller will increase your speed under sail while significantly improving marina handling.

One of the most debatable and divisive issues in sailing is the varying schools of thought as far as the best sailing propeller is concerned.

Whether you believe in using the motor as your main propulsion or you fall in the purists' category who believe that a propeller should only be used for getting in and out of a marina, one thing is for sure: propeller drag is and has always been a major issue for sailboats since the invention of propellers.

While fixed three-blade props are essential in providing superb motoring performance, they can negatively affect your speed and performance when under sail. To avoid this, you should consider choosing between folding propellers and feathering propellers.

Fixed propellers are known to cause significant drag that can negatively affect your sailing speed and performance when under sail. This means that we're only left with two options: folding propellers vs. feathering propellers.

The debate generally revolves around whether you should let the propeller rotate while sailing or put a stop to the spin

Studies have proven that folding and feathering props can create less drag and in turn enhance your boat's speed and performance, especially when compared to fixed props.

But even after discarding fixed props for the considerable amount of drag that they cause, we still have to choose between folding propellers and feathering propellers.

This is what this article is all about: folding propellers vs. feathering propellers. At the end of this read, you should be able to differentiate the two and choose the right one for your sailing escapades.

Table of contents

The Importance of Choosing the Right Propeller for Your Sailboat

Your sailboat's propeller plays an integral role in enhancing its speed and performance. Whether you're planning to make a long-distance passage or trying to outrun an approaching storm, you probably have realized that an extra knot makes a whole lot of difference. An extra knot can not only save you time but also be the difference between life and death, so it should never be taken for granted.

That's not all, choosing the right propeller brings with it some sort of a feel-good-factor knowing that you're getting the best from your sailboat. It will give you the peace of mind that you deserve when out there on the water while enhancing your boat's performance and speed.

Unfortunately, choosing the right propeller for your sailboat isn't a walk in the park. If anything, choosing between a folding propeller and feathering propeller brings forth a multi-dimensional problem in terms of the level of performance, efficiency, price, maneuverability, safety, and many more. This is exactly why you should know what they are, what they will do to your boat, and the best one to go for.

Folding Propellers

A folding propeller is essentially a type of propeller that is often mounted at the aft end of a boat's keel. It is designed in such a way that its blades automatically fold out when the engine is used to power the sailboat and fold back when the boat is under sail and the engine isn't working. When the engine is on, folding propellers will spin outwards by a centrifugal force. On the other hand, the water flow forces will push the propellers back when the engine stops.

Folding propellers come in various forms and may range from the most basic types to highly sophisticated geared folding propellers. The most sophisticated ones might be costly but are quite efficient and will provide top-notch performance both ahead and astern while significantly reducing all forms of drags.

We have to note that folding propellers can be ideal for easily driven lightweight sailboats or if you do not want to ignore the unwanted drag and significant loss of speed. Folding blades are also essential in racing circles. They generally fold backward thereby reducing drag significantly and increasing speed and performance under sail.

Benefits of Using Folding Propellers

You've probably been wondering why many sailboat owners have been choosing to use folding propellers on their boats. Well, the benefits that these types of propellers bring to your sailing adventures in terms of speed, performance, and safety are unmatched.

Here are some of the benefits.

Reducing Drag

Numerous tests have consistently shown that folding propellers create the least amount of drag when sailing, especially when compared with feathering propellers or fixed propellers. The two-blade versions of folding propellers are the most efficient in reducing drag, especially when going astern.

Most two-blade folding props can perform just as well as three-blade folding props. However, their simple design of opening independently of each other can sometimes cause imbalances and vibrations, especially if one of the two blades open or close more than the other.

There are also three-blade and four-blade propellers that bring to your sailing game an interesting overdrive characteristic. These blades generally work by reversing automatically when going astern. This feature is important when the engine is on as it can be essential in saving fuel when using the engine to sail in calm conditions.

Folding props generally have better thrust when moving forward than feathering propellers but this will, of course, depend on the pitch as well as the shape of the blades. The prop will go astern if they have a weak point. This is because they rely on the centrifugal force to hold the blades open against the force trying to close them. You have to keep in mind that the blades might not be as efficient as it if going forward if the blades are open.

Offering Safety

The blades of folding propellers don't usually stick out as they do on feathering props or fixed propellers. This means that there are no chances of the prop catching debris or any marine creature. Needless to say, such issues can lead to a loss of steering ability and ultimately cause an accident. In short, your safety is much better if you're using folding propellers.

Greater Maneuverability at the Dock

Folding propellers are generally designed with powerful shapes and hydrodynamic designs that can give your boat greater maneuverability like you would at the sea. These props are designed with superior stopping, forward, and reversing power.

As we noted earlier, folding propellers are the most efficient in reducing drag, which generally affects the speed and performance of your boat. So by installing a folding prop, you will improve your sailing performance and speed by nearly 15%. Your boat will be faster and the voyages will be more enjoyable even in lighter winds.

More Comfort

In an ideal sailing situation when the wind is optimal and the weather is calm, you're likely to hear the sound of the propeller, especially if it's a fixed propeller. The resultant noise can be frustrating but this should be an issue in folding propellers. If anything, the noise levels will be as low as the drag. This is because most folding props are designed with strong built-in shock absorbers to reduce the noise levels.

In short, folding propellers are ideal if you want to reduce noise and vibration that are common in fixed blades.

Great Value for Money

If you've owned a sailboat before, you already know that having a propeller that's designed with various moving parts can be costly in terms of repair and maintenance. This is essentially why many sailboat owners prefer props with just a few moving parts.

As such, folding props can be ideal since their only moving parts are the blades. They are also structured with smooth acting gears and strong materials to ensure durability without any need for greasing, rebuilding, replacements, or maintenance. In essence, folding props will ensure that you spend most of your precious time sailing instead of being at the dock fixing your boat.

Similarly, folding props are known for having lower initial purchasing cost than feathering props. They have a simpler design, which significantly reduces the purchase costs. In short, folding props are more affordable than feathering props.

Cons of Folding Props

Despite these numerous benefits, folding propellers have noticeable downsides that we have to highlight. They include:

• ‍ The fixed pitch that cannot be removed or changed once fitted. If you have to change or remove the pitch, you'll have no choice but to seek the services of a propeller expert.
• Although this may vary depending on the brands, folding props have simple designs that tend to wear out the fastest when compared to feathering props.
• Folding props have inadequate reverse thrust, so you'll have to be very skillful to maneuver tight dock spaces.
• The gears are most likely to be exposed to the marine environment and, therefore, will wear out quickly.

Are Folding Propellers Ideal For Your Boat?

Folding props can be ideal for you if you have a small or medium-sized sailboat with moderate engine power. You'll not only attain extra speed under sail but drag will be a thing of the past. Additionally, folding props can also be ideal for motor sailors and larger boats. So if an extra knot is essential for you, folding props might make much sense.

Again, you'll have the peace of mind knowing that your safety is guaranteed as far as your boat's propeller catching debris or causing an accident is concerned. Its design can prevent seaweed from getting tagged along or anything that might make you lose your steering ability and perhaps cause an accident.

Feathering Propellers

Feathering props operate exactly as the name suggests: the prop blades feather when the engine is on neutral or shut down. They generally feather in the passing water flow in the same way a sail positioned head-to-wind would. It has a small profile that is essential in reducing drag while enhancing speed and sailing performance.

The blades of a feathering prop are designed in such a way that they set themselves perpendicularly to the water flow. This gives them a neutral cutting edge to the water, which makes the blades almost flat. As such, such types of props can be less efficient when sailing ahead since the pitch will be reversed when the engine is going astern. Fortunately, you can repitch your feathering prop by simply adjusting the point at which the flipping blades meet but you'll have to move the gears a couple of notches.

Benefits of Feathering Propellers

Here are some of the benefits of using feathering propellers.

Offers Superb Maneuverability

Generally speaking, feathering props are positive in their function. The blades or the feathering props will be opened by the torque of the shaft. It doesn't matter whether it has seaweed or not, the feathering props will open because of the torque of the shaft that reduces unnecessary shock load. The fact that it has the best thrust in reverse and commendable thrust when moving forward gives it superior maneuverability even in tight docking situations. You'll also not need any skills to maneuver the boat at the dock.

Offers Amazing Reverse

Feathering propellers are widely popular not just because of the superior maneuverability that they bring to your sailing adventures but also because of their incredible reverse features. The blades can rotate 180 degrees in turn of the shaft, thereby giving them a very high level of efficiency on both the reverse and forward thrust.

This will improve your level of control even on the reverse while decreasing prop walk. In essence, the feathering props are much better than fixed props or folding props in reverse. They should, therefore, be your first choice if you're looking for a prop that can give you complete control of your sailboat even in tight spaces. These types of props are also very durable as they're more robust in construction than folding props.

Even though not on the same level as folding props in terms of reducing your boat's drag, feathering props are much better than fixed props. To put it into perspective, a 26-foot sailboat is likely to create about 50 pounds of pull if it has fixed props while the same boat would create 4 pounds of pull if it's fitted with feathering props.

Adjustable Pitch

Unlike folding props that have fixed pitches, feathering props do have pitches that you can easily adjust to optimize the performance of your boat. The systems used by each brand can vary but you can set independent reverse and forward even when on the water. This can also help in reducing the prop walk.

Cons of Feathering Propellers

The most noticeable downside of feathering props is their expensive prices. Feathering props generally cost twice as much as folding props and this can be a major hindrance if you're on a tight budget. You'll also have to service and maintain the props due to their complex designs. Again, you might have to deal with a given level of drag, which makes them less efficient as far as speed and performance are concerned.

Are Feathering Propellers Ideal for Your Boat?

Simply put, feathering props can be ideal for you if you're looking for efficient maneuverability, especially at the dock. These types of props allow you to thrust forward and reverse even in tight docks. As such, this can be a good option for novice sailors as there are no technical skills required to maneuver the boat even in tight conditions.

To this end, we hope that you can make the right decision in choosing between folding propellers and feathering propellers. While they are much better than fixed propellers, the most ideal one for your boat will certainly depend on your specific needs.

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Daniel Wade

I've personally had thousands of questions about sailing and sailboats over the years. As I learn and experience sailing, and the community, I share the answers that work and make sense to me, here on Life of Sailing.

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Of propellers

Welcome to bruntons propellers.

Whatever type of vessel you require a propeller for you can be sure that Bruntons have the solution – not just any solution but exactly the right one. Why? Because Bruntons are the one company in the world that designs and manufactures just about every type of propeller in regular use today. We have no reason to try and get you to settle for second best because we will have the perfect answer.

The ECOSTAR

A new version of the Autoprop called the Autoprop Eco*Star has been developed to propel the rapidly growing number of hybrid and purely electrically driven craft, both motor and sail, which are being launched around the world.

The Autoprop

Autoprop’s unique design and superb build quality make it the first choice feathering propeller among cruising yachtsmen the world over, with drag reduction when sailing by at least 85%, and a unique ability to change pitch automatically to suit prevailing wind and sea conditions when motoring or motor sailing. 

The Varifold

Varifold – the folding propeller for larger cruising yachts, cruiser racers and purely racing yachts of all sizes with engines from 10 to 1000hp.

The Sigmadrive

Bruntons SigmaDrive is a brand new 21st Century solution that is already an award winner and provides effective anti-noise and anti-vibration solutions of the highest order.

Bruntons and our agents around the world hope to be exhibiting at as many boat shows in 2023/2024 as possible. Please keep an eye on this page and we’ll hopefully be adding more shows soon.

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Ewol propellers make maneuvering easier (reduce inertia) and increase sail speed and optimize engine speed.

EWOL adjustable pitch propellers are made of stainless steel alloys that represent the highest technology in terms of marine corrosion and galvanic corrosion resistance, and are also equipped with the most refined technical solutions that make it unparalleled on the market.

EWOL feathering propellers can be fitted on sailing boats with both traditional (endothermic) and electric engines and with both mechanical and hydraulic inverters. The components of EWOL propellers are made of super-duplex stainless steel alloys, developed by the steel industry for extremely heavy tasks.

EWOL regularly presents new versions of its products with increased performance, and is now also working on developing additional innovative products that will come out in the short and medium term. Nowadays, anyone seeking a truly reliable product that performs over time, solves boat manoeuvrability and sailing speed problems, and is always up at the cutting edge of technology and materials, should install an EWOL propeller on their boat.

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• Systems & Propulsion

Folding vs. Feathering Props

With a new engine, mahina tiare gets a new streamlined screw..

For the past 40 years we’ve sailed an average of 10,000 miles annually between Australia, Alaska, Antarctica and Spitsbergen motoring or motorsailing between 400 and 600 hours, depending on the area – more hours in high latitudes of Antarctica and the Arctic, fewer in the tropical trade winds.

Our HR 42 came with a fixed three-blade prop which served us well when pushing bergy bits out of the way in Patagonia, Antarctica and Alaska, but obviously slowed us down in light airs. When we had our current Hallberg-Rassy 46 built in 1996, anticipating better sailing performance, we opted to install a Max-Prop as that was acknowledged as the best option at that time.

Max-Prop has been around since the early 70s and is a proven design, but after 18 years and 190,000 miles of use, we had the prop rebuilt three times, each time costing between $800 and $1,200. The first time the prop was rebuilt by Henleys, an Auckland prop shop, and the other two times by PYI, the U.S. importer/distributor located near Seattle. I was told that the rebuild included brazing more bronze on to the props inside working surfaces followed by machining the built-up surfaces down to original tolerances. When I enquired what I could do to extend the period of time between rebuilds, PYI said, More grease! So for 15 years, we not only greased the prop before launching at the start of our season, but also mid-season going underwater with mask, fins and grease gun to do so.

The advantages of the Max-Prop are very little drag when sailing as the prop instantly feathers unless the engine is engaged, no freewheeling in neutral, adjustable pitch, and incredible stopping power in reverse. Max-Prop can literally bring a boat from 6 knots to a dead stop in a boat length. This feature has kept us from nailing coral heads at least twice. The ability to adjust the pitch to maximum engine efficiency improves fuel economy and the newer Easy model Max-Props can be adjusted in the water without having to disassemble and reassemble the propeller, which is a substantial improvement over the earlier Classic version. We did encounter (and frequently use to our advantage) fairly substantial propwalk.

The disadvantages are that when the Max-Props feathers, the blades are still open and prone to fouling lines and kelp. During our 2008 Atlantic crossing we had to get in the water with mask and fins three times to remove cargo nets and large 3-inch floating lines from the prop. The Atlantic Ocean has a garbage gyre similar to, but smaller than the Pacific Garbage Patch, and we must have found the edge of it during our 2008 crossing. Last month, we completed the identical route from the Canary Islands to Antigua with only one sighting of trash and favorable winds that allowed us to basically sail the rhumbline. As a funny side note we were once making landfall at Fastnet Rock when a smaller boat passed us under sail. Trim as we might, we couldn’t catch them and only when they were several boat lengths ahead did Amanda think to check astern only to discover a fat turquoise rope trailing behind. The rope, obviously was not ours, was caught on the prop and we wondered how long it had been there as we’d not used the motor for several days.

During a 2015-2016 winter refit in Sweden, after reading the results of two European propeller efficiency tests and after speaking with several owners who had switched from Max-Prop to Flexofold, I had a Flexofold prop installed. Jack Skrydstrup, Flexofolds Danish manufacturer recommended the size and pitch, and the boatyard installed it without problems.

In comparison the stopping power is not nearly as good as with the Max-Prop, and the prop freewheels when the engine is shut down in neutral. Weve found that shutting down in slow forward solves the freewheeling issue. Strong on the Flexofolds plus side are blades that feather aft, instead of extended, so they’re less likely to snag lines or kelp. We notice almost no propwalk in reverse. In addition, cost of ownership is reduced as there doesn’t appear to be a need to rebuild and there are considerably fewer spare parts to carry.

However, the improvements in efficiency are difficult to quantify as we also repowered at the same time, switching from a 95 hp. to 75 hp. engine, but our top speed rose 0.7 knots, and fuel consumption on an identical Atlantic crossing dropped from 1.33 gph to .83 gph.

On the service side, PYI, the U.S. importer/distributor of Max-Prop is renowned for their customer service, doing a superb job of shipping spare parts immediately and quickly handling rebuilds from their shop near Seattle. Flexofolds Jack Skrydstrup is helpful, and ships quickly, although shipping is factory-direct from Denmark. Ive only heard one incident of an owner needing parts during European summer vacation period when shipping was delayed slightly.

Amanda and John Neal spend seven months at sea sailing 10,000 miles a year while leading sailing training expeditions. The have more than 500,000 sea miles combined experience.

Nigel Calder, author of The Boatowners Mechanical and Electrical Manual shared propeller data collected during the course of his recent hybrid propulsion experiments. Here’s his summary: “We tested Flexofold, three Goris, two Volvo-Penta four–blade folding props, three Brunton Autoprops, a Brunton Varifold, and a fixed pitch, which was undersized so not a fair comparison – it just happened to be available. The objective of these tests was to collect baseline data for other purposes. As such, the propellers were not necessarily properly matched to the boat and these are not apples-to-apples comparisons. “The Flexofold, Volvo-Pentas and Varifold had similar efficiencies, but from an engineering perspective the Flexofold was the simplest design and easiest to fit.”

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Our experience with Flexofold is that they have not stood behind their size / pitch recommendation. Great prop otherwise — well made and much more efficient than our Max Prop.

I am considering installing a Brunton Autoprop on my 34’ Vashon cutter (26’ LOD), 6500# displacement. Has anyone had experience with these props and/or what is your opinion of installing this type of feathering prop?

It would be helpful if you labeled the pictures so that us less knowledgeable sailors knew what prop we were looking at. Very good overview article considering all of the variables involved. It provided some insight. By way of an example, I tried 3 different props on my dingy before I found the best fit for my needs; a boat is more complicated.

I absolutely love the concept of the Autoprop. After having held one at a boat show, and seeing a cutaway model, I still can’t figure out how it works, but that doesn’t stop it from being brilliant. Alas, when we re-propped our Marshall 22 catboat, there wasn’t enough room for any of the Autoprop line.

We chose a 12″ three-bladed Featherstream and are very happy with it. On the downside, you have to remove a pitch “cassette” (a specifically-sized arc of metal) and replace it with a different size in order to change the pitch. But on the upside, man is that simple. You don’t even have to fully-disassemble the prop to do it. A fellow at the boatyard watched wistfully as he talked about having to disassemble is feathering prop and try to figure out which detent a screw would fit into when covered with grease.

The price was also quite reasonable, and service from Canada has been great.

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Autostream Propellers

Autostream Propellers feature high strength 2507 super duplex stainless steel blades allowing a very thin low drag blade design, symmetrical in section and virtually flat faced, resulting in minimal drag. The Self Feathering Autostream Propellers are available in 3 blade and 15 to 20 inches in diameter If you do not see what you are looking for, or are not sure what you need, please call us at 866-790-7767 or email us at [email protected]  

The geared slipstream folding propeller design keeps blades synchronized, allowing the blades to fold back properly regardless of the propeller position, even at low speeds - no crawling into the bilge to position the shaft when racing. slipstream propellers offer all stainless-steel construction for superior life using low carbon 316l grade stainless steel. slipstream propellers are available in 2 or 3 blade and propeller sizes from 14 to 18 inches diameter. if you do not see what you are looking for, or are not sure what you need, please call us at 866-790-7767..

Autostream Self Feathering Propeller 15"

15" Autostream 3 Blade Self Feathering Stainless Steel Propeller fits shaft diameters 1" thru 1 3/8"..

Autostream Self Feathering Propeller 16"

16" Autostream 3 Blade Self Feathering Stainless Steel Propeller fits shaft diameters 1" thru 1 3/8"..

Autostream Self Feathering Propeller 17"

17" Autostream 3 Blade Self Feathering Stainless Steel Propeller fits shaft diameters 1" thru 1 3/8"..

Autostream Self Feathering Propeller 18"

18" Autostream 3 Blade Self Feathering Stainless Steel Propeller fits shaft diameters 1" thru 1 3/8"..

Autostream Self Feathering Propeller 19"

19" Autostream 3 Blade Self Feathering Stainless Steel Propeller fits shaft diameters 1" thru 1 3/8"..

Autostream Self Feathering Propeller 20"

20" Autostream 3 Blade Self Feathering Stainless Steel Propeller fits shaft diameters 1" thru 1 3/8"..

Better Sailing

Fixed Vs Folding Vs Feathering Propeller

Out of sight, out of mind goes the saying, so it often is for your boat’s propeller. Crucial as this piece of equipment is to your safe and rapid movement from a to b, it often receives very little attention. You simply set it and forget it – until something goes wrong. That’s a shame because most new boats are fitted with fixed-blade propellers as standard, and older boats often have them too. While that is fine when the engine is running ahead, a fixed propeller is inefficient astern. It applies real drag to a boat under sail.

Tests vary in their scientific-ness, but  data suggests that a fixed prop that is locked creates at least 20 times as much drag vs a folding or feathering propeller at 5kt. In speed terms, that equates to some 20% more pace with a folding or feathering propeller vs a fixed one. That data suggests that folding and feathering props are much better than fixed.  Crossing the North Sea from Harwich to Ijmuiden means that it could save you four hours.

Folding or Feathering?

Folding propellers – where the blades close up around the central boss – are marginally more efficient in sailing mode than a feathering prop, that has blades that simply rotate to a position parallel to the direction of movement. This makes them the racer’s choice, but it is a narrow margin and pales into insignificance next to a fixed prop. A feathering prop is nearly as efficient as a folding prop when going ahead and typically a bit better astern. Feathering blades can be more suited to long keel boats where the prop is enclosed, providing insufficient space for a longer folding prop.

On the other hand, a folding prop is less apt to tangle with fishing pots and waterborne debris. In the early days of these designs, folding props could be reluctant to fully deploy when going astern. However, manufacturers claim this tendency has now been eliminated. Tests suggest that they are far more effective astern at high revs rather than low and can cause a loud clunking noise when they deploy. 

Propeller Diameter

This is a measure of the prop’s size and refers to the width of the circle that the blade tips turn through. It is twice the distance from the center of the boss to the tip of a blade. In general, the more powerful your engine, the bigger the prop diameter needed to utilize that power effectively.

Propeller Pitch

The blades of your propeller slant or curve forward (or back in reverse) – this is what part of what generates the motion. This pitch is usually measured in inches and refers to the distance the propeller would advance in one revolution if it gripped the water perfectly. Imagine your prop is a screw; the pitch is how far into the wood the screw advances with one full turn.

The steeper the pitch, the more work the engine must do with each revolution. A standard pitched propeller will ensure that the engine can just reach full rpm at full throttle. Some sailors like being overpitched, however. It puts more strain on the engine, which means it will never reach peak revolutions, but it’ll keep the boat moving a bit faster through the water until peak power. Turning over more slowly, the engine is a bit quieter and more efficient.

Some props have a variable pitch, automatically adjusting to the pace of the boat and revs of the engine. Others allow the pitch to be changed via a turn of a screw on the boss or require the boat to be hauled out.

Prop Blade Number

This is essentially down to you. Fewer blades mean less drag – hence the reason that so many fixed props are two-bladers. But with the exceptionally low resistance of a fixed or a folding prop, this is barely an issue. On the other hand, there can be more vibration with a two-blade model than a three or more blader. And more blades give more power. Most cruising yachts have three blades.

Best Folding and Feathering Props

The Gori is a folding prop that claims to have the thrust of a fixed prop. Made from nickel aluminum bronze, the blades are geared so that they cannot open or close independently. They pivot through 180 degrees to give the same pitch in forward and reverse, which means optimum speeds in both directions. Uniquely, Goris have an ‘overdrive’ function for motor sailing, which deepens the pitch of the prop to give the same power from lower engine rpm.

With the lowest drag of any folding prop, according to some German tests, Goris are used by the Volvo Ocean Race boats and many of the racing one-designs, as well as cruising brands.

Bruntons’ feathering propeller is a technical marvel with either two or three blades that rotate perpendicular to the prop shaft. Because each blade’s weight is offset, they will rotate through 180 degrees between forward and astern, giving them the same optimum pitch in both directions. Free to rotate on their axis, the blades will adopt varying pitches, according to the needs of the boat.

So, when you are motor sailing, they pitch up to account for the driving force of the sails, reducing fuel consumption and engine rpm. This feature should also reduce prop walk astern.

Also manufactured by Bruntons in Essex using high-quality nickel aluminum bronze, the Varifold is designed to appeal to racers and fast cruisers. As a folder, it offers less resistance in sail mode than its Autoprop sister. 

The company claims a unique design for the blades of the prop that cuts noise and vibration. A helical pitch, including reduced pitch towards the blades’ tips, reduces pressure and noisy pulses against the yacht’s hull.

Featherstream

This UK-built propeller is manufactured using aluminum bronze for the hub and stainless for the blades. There is no standard spec for their props because Darglow prefers to talk through a client’s requirements in detail first. 

The pitch on a Featherstream is determined by the pitch cassette installed with it. This can’t be altered when the boat is in the water. Still, it is always possible to send off for a differently pitched cassette from Darglow and install it via a 10-minute operation when the boat is hauled. If you send the old cassette back, this is cost-free. 

The blades are completely flat for frictionless sailing and rotate through 180 degrees for optimum power ahead and astern.

Maxprop blades are flat and pivot through 180 degrees so that the leading edge is presented in both forward and reverse – making for excellent thrust either way. 

Pitch can be changed in 2-degree increments at the turn of a screw, which can even be done in the water with the Easy and the Whisper models. It is not quite the variable pitch that the manufacturer claims, but it does offer some flexibility. The blades are linked by gears, so they open and close at the same time. 

Maxprop says its products are particularly good for catamarans.

Unlike all the other propellers featured here, the blades of the Kiwi Prop are a special nylon-glass composite called Zytel. Glass may seem an odd choice for a propeller. Still, the material is incredibly tough, lighter than metal, and corrosion-free. It is also much cheaper than bronze, a fact reflected in the lower retail prices. The manufacturer also points out that the blades are sacrificial in the event of a collision and much cheaper to replace than potential repairs to the stern gear. 

The blades are fatter than some but symmetrical, free to rotate around their axis for excellent feathering. The boss allows the blade assembly to rotate 100 degrees, offering adjustable pitch ahead and maximum pitch astern for more power at low speeds. 

Kiwi is also developing a two-blade folder. 

This feathering prop is entirely made of 2507 duplex stainless steel for exceptional strength and resistance to corrosion. It features narrow blades that swing through 180 degrees in reverse. 

Pitch is independently set for ahead and astern and can be easily adjusted – as can direction of rotation, if a change of engine necessitates it.

The folding prop from Seahawk is also in stainless steel – but this time low carbon 316 for long life. 

The blades are geared, so they are synchronized, and the bushes can be replaced easily when worn. Plastic bump stops prevent the prop from clunking when it swings open, and the same polyurethane forms side plates to stop metal-on-metal wear. Seahawk provides a five-year warranty.

The Flexofold uses high-quality nickel aluminum bronze in its construction. Being water lubricated, its gears need no grease. Its simplicity and competitive price have made it the go-to prop for many boatbuilders. It has large shock absorbers for quiet opening, and in tests, it performs well both ahead and astern. Also available in a special race variant with a corrosion-free composite boss that saves 2.8kg of weight.

The Variprofile is a robust prop, built to order in ice-class nickel aluminum bronze for an extremely long life. Like most feathering props, the blades are flat and thin, and they rotate 180 degrees in reverse to offer the leading edge in both ahead and astern. A simple turn of a screw is enough to change the pitch, which can be independently set in both directions – ahead, it is all about optimizing thrust, while in reverse, it is about reducing prop walk. A patented multidisc brake acts as a shock absorber to eliminate the clunk when you engage the prop. Its short hub makes the prop really suitable for long keeled boats with a small prop aperture.

Variprofile

Similar to its Variprop, Variprofi le is SPW’s cheaper, small-boat feathering prop. It is mass-produced for modern serial yachts with engines up to 140hp. Otherwise, it has many of the same features as its custom-built sister, including micro-adjustment for the forward and aft pitch.  

Peter is the editor of Better Sailing. He has sailed for countless hours and has maintained his own boats and sailboats for years. After years of trial and error, he decided to start this website to share the knowledge.

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Why a feathering propeller for my Sailboat?

Published: 12/08/12 at 01:52pm.

Good question. With all of the low drag sailboat propellers on the market today. Why should you buy a feathering propeller?

To be upfront I am jaded. I have been selling Max-Prop feathering propellers for over 27 years. Wow, I still can’t believe I have been at PYI for that long, thanks to Kevin and Frederic for building such a great company. Sorry I digress.

To be simple the advantages of a feathering propeller are threefold.

First, they are positive in their function. The torque of the shaft opens the blades, even if it is encrusted in marine growth it will open. Folding propellers use centrifugal force to open, meaning the shaft has to be rotating before there is enough force to open the blades, this causes quite a lot of shock load to the drive train.

Second, a feathering propeller has amazing reverse. As the blades rotate 180 degrees in ¾ turn of the shaft a feathering propeller has the same efficiency in reverse as in forward. This increase in efficiency decreases prop walk and improves control in reverse. A fixed propeller cuts with the trailing edge and against the cupping on the blades, it loses about 80% of its efficiency in reverse. Similarly, the twist of a folding propeller's blade tries to fold the blades in reverse, presenting a less than efficient attach angle.

Third, a feathering propeller is a low drag propeller. On an average 36 foot boat, a fixed two-blade would create around 70 pounds of pull if it were attached to a scale. A two blade feathering Max-Prop would only create 4 pounds of pull. Quite the difference, think of pulling a 5-gallon bucket behind your boat, that would be a drag.

Cheers, Fred Hutchison

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Custom yacht fabrication & Engineering

Feathering propellers for sailboats from jbc engineering.

Established in 1974 by yachtsman, Jack Christoffersen, JBC Yacht Engineering is still Australian owned and run. Based at Carreening Cove in Sydney Harbour, our staff are experienced, knowledgeable, and passionate about all things marine. 

Now owned and run by experienced engineer, George Atkinson, JBC offers a wealth of experience in engineering services, specialising in both modern and traditional machining and fabrication techniques. We provide services such as welding, design and repair on site, using all materials and metals available.

JBC manufacture Hydralign Feathering Propellers and Seahawk Feathering and Folding Propellers, Australia's largest range of feathering propellers for sailing yachts. Tested in some of the world’s toughest waters, Hydralign yacht props are more efficient and durable, outperforming their competitors time and time again. Australian made and owned since 1990, our feathering props for sale are designed to get boats reacting positively in both forward and astern. With fewer working parts and positive incremental pitch adjustment, Hydralign ensures better performance and smoother transitions.

Learn More About Our Full Feathering Propellers

We have a wide range of feathering props suitable for sailboats and yachts. If you have any questions about our sailboat or yacht propellers for sale, feel free to get in touch on +61 2 9188 0825. Our team are highly knowledgeable in all things marine and will be happy to help you buy the right prop for your vessel.

seahawk feathering and folding propellers

JBC Yacht Engineering are now the proud owners of the famous and reliable line of Seahawk folding and Feathering propellers. JBC can now provide an even wider range of high quality sailing propellers including the excellent Slipstream folding propeller, perfect for serious racers. We are proud to carry on the legacy of another great Australian made product.

Production is gaining momentum and we hope to be producing our first Autostream Feathering Propellers Mid 2023 .

Limited stock of Slipstream folding propellers are available now.

Please get in touch regarding new prop sales and servicing or repairs of Seahawk Autostream and Slipstream propellers. For more information please visit www.seahawk.com.au

hydralign propellers

Proudly Australian made, Hydralign is a trusted, efficient and robust full feathering propeller ideal for sailboats and yachts.

marine engineering

We specialise in custom marine fabrication and machining, everything from made to measure sheaves to large scale bimini frames.

JBC has a well-established engineering repairs shop and can service architectural, commercial, automotive and domestic engineering needs.

hydralign props

HYDRALIGN FEATHERING PROPELLERS MAXIMISE YACHT PERFORMANCE WITH MORE EFFICIENT USE OF ENGINE POWER AND POSITIVE INCREMENTAL PITCH ADJUSTMENT TO GET THE MOST OUT OF YOUR YACHT. BUY YOURS ONLINE TODAY!

Contact JBC Engineering

Please send us any marine or non-marine engineering related questions, or give us a call on +61 2 9188 0825

Our Address is: 4/1 Bradly Avenue, Milsons Point, NSW, 2061

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FIND YOUR NEXT FLEXOFOLD FOLDING PROPELLER

Flexofold develops, manufactures,, and sells the most efficient folding, propellers for sailboats and, multihull yachts on the market..

Get a specified propeller recommendation for your sailboat

Our folding propellers are available as 2-bladed, 3-bladed, and 4-bladed in multiple sizes and pitches. All delivered for both shaft- and saildrive installation.

100 % FIT ON ALL COMMON SAILDRIVES

The Flexofold propellers fit perfectly on all common saildrives and are widely used by most of the recognised boatyards worldwide – including Beneteau, Jeanneau, Lagoon, Elan, Hanse Yacht, Dehler, Saffier Yacths, Halberg-Rassy and many more!

100% fit on all common shafts

The Flexofold propellers are designed to fit perfectly on all common shafts following the ISO; SAE and IMP standards, and are widely used by most of the recognized boat yards worldwide.

Worldwide delivery

Flexofold propellers  are delivered all over the world directly from our factory in Vejle, Denmark. No matter where you live or where your boat is located, we ship your new propeller by UPS courier service – directly to your address at very competitive costs. In most cases, we ship your new propeller within 3-5 working days from placing the order / receiving payment.

Our experience - your guarantee!

We pride ourselves in direct contact and dialogue with our customers, shipyards, and dedicated sailors from all around the world. This is why we can ensure that you get the right guidance and the best possible propeller for your sailboat!

Saildrive Propellers

Flexofold folding propellers for  Saildrive installation

Shaft Propellers

Flexofold folding propellers for mounting on Shaft

Spare Parts

Find  spare parts  for your propeller  here    

The best test for a propeller is the one carried out by the sailor himself!

Find the answers to the most frequently asked questions about folding propellers

Enjoy the performance and safety benefits that our foldable propellers provide

CUSTOMER REFERENCES

The Flexofold 3-Blade 17x13-3L/R propeller went on after the first attempt. The motors—2x Yanmar 3JH5—come to a nominal speed of 3000 RPM and the Outstar 48 goes at the speed of 9.5kn

Andreas Bock

The new outstar 48 with twin flexofold - germany.

Adding the 3 bladed Flexofold was the best thing ever. Should have done it years ago. Better performance under sail and power. Cut fuel consumption in half!

Mark Schneider

Smarter charter ltd. - usa, buy directly from the flexofold factory.

Get an offer for a Flexofold folding propeller.

Seahawk Low Drag Stainless Steel Feathering and Folding Sailboat and Yacht Propellers

Seahawk's autostream and slipstream propellers have moved to nsw.

Autostream S1/S2 3 blade feathering Yacht propellers

Feathering Propeller Features :

• Strong reverse thrust better than a folding or fixed blade propeller
• All major parts cast in 316 and 2507 stainless steel
• Easy to replace bronze and acetal bushes
• S2 model has a rubber insert to absorb shocks and can be replaced
• Simple external pitch adjustment
• Sizes from 15 to 20 inches diameter
• Rated for up to 75 horse power
• S1 model fits taper shafts up to 1-3/8 inches diameter
• S2 model fits 17 Spline Sail drives
• S2 fits 109mm Gearcase Sail Drives like : Volvo 130/150 and Yanmar SD20 SD31 SD50 SD60
• S2 model does not match : small 89mm Lombardini Sail Drives and small Volvo 120s Sail Drives

Slipstream S5 3 blade folding Yacht propeller

S5 Folding Propeller Features :

• Less chance of catching kelp and ropes than a feathering propeller
• All major parts cast in 316 stainless steel
• Easy to replace bronze blade bushes
• Sizes from 14.5 to 18.5 inches diameter
• S5 model fits taper shafts up to 1-1/2 inches diameter

Slipstream S7 3 blade folding sail drive Yacht propeller

S7 Folding Propeller Features :

• Rubber insert to absorb shocks can be replaced
• S7 model fits 17 spline sail drive shafts like
• Volvo 130/150 and Yanmar SD20 SD31 SD50 SD60

Slipstream S4 2 blade folding Yacht propeller

S4 Folding Propeller Features :

• Less drag than a 3 blade folding or feathering propeller
• Sizes from 14 to 20 inches diameter
• S4 model fits taper shafts up to 1-1/4 inches or 30mm diameter

Slipstream S6 2 blade folding sail drive Yacht propeller

S6 Folding Propeller Features :

• S6 model fits 17 spline sail drive shafts like