sailboat propeller drag

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Reduce Drag When Sailing With A Folding Or Feathering Propeller

Learn how this time-tested piece of running gear can give your boat a power boost under sail.

Photo: Stacey Nedrow-Wigmore

One thorny debate among sailors is whether it's better to let a propeller freewheel (rotate while sailing) or to lock the shaft and hold the prop steady. Whichever camp you fall into, there's no denying that a fixed prop creates drag that slows down your boat.

Consider this: If your boat has a fixed three-blade prop, you could be losing as much as a knot of speed when sailing (as verified in an independent test of several props by the author aboard his own 33-foot sloop). In other words, if your boat typically cruises around 5 knots, switching to a folding or feathering propeller could ramp up that speed to 6 knots — that's a 20% increase! Over a typical 30-mile voyage, that translates to arriving one hour sooner.

Folding and feathering props are nothing new and have been around in one form or another for more than half a century. Early props had just two blades that relied solely on centrifugal force to open them. While these props work well enough for many sailors, they have a few shortcomings: They don't work too well when maneuvering around the docks, especially when backing. And should one blade open slightly more than the other, excessive vibration can occur, causing wear to the shaft log and cutless bearing.

Newer types of folding props, such as the Flexofold , may have two or more blades interconnected to each other with a gear mechanism. This ensures that when the shaft starts rotating, they open symmetrically. Other brands include Gori Prop , Varifold , and Slipstream .

However, folding props may not work for some boats, especially if the rudder is close to the propeller hub preventing the propeller from completely folding. In this instance, a feathering prop, such as the Max-Prop , may be a better choice. Other brands include Kiwiprop and Variprop . With a feathering prop, the blades are symmetrical and rotate around a central pivot point and offer as much thrust in reverse as they do in forward gear — a boon for getting into a tight slip. When sailing, the blades align themselves with the flow of water, reducing drag.

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Yachting Monthly

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Lock your prop, or let it spin?

Emrhys Barrell
June 11, 2015

To reduce drag when you’re sailing: should you lock your prop, or let it spin? Emrhys Barrell’s conclusive test settles this long-running debate, once and for all

Some sailors lock their prop under sail, others let it spin Credit: Graham Snook/YM

The debate has raged for as long as sailing boats have had propellers, and everyone has their own theory. Brunel probably tussled with it when he designed Great Britain, and it has certainly kept waterfront bars the world over humming with arguments ever since, as to which mode gives the least drag when you are sailing.

There are two sides to this endless argument. Lockers say that if the prop is spinning, some force is causing it to spin, and that force creates drag, which slows the boat down. Spinners reply that dragging a fixed three-blade prop through the water causes much greater drag, slowing the boat more. In fact, both are correct to some degree, but which causes least drag? That is what determines whether you should lock or spin, and that’s what we set out to measure.

When the prop is fixed, the water flow hitting the blades is deflected to one side, causing drag. If the prop is spinning, the water will be deflected, but through a lesser angle, causing less drag.

To visualise this, imagine rushing through a revolving door, just as one of the panels has gone past you. If the door is spinning, and you bump into that panel, you won’t get much of a shock. If the door is stationary, however, you will be nursing a bruised nose for some weeks.

We used electric power and sheltered water to eliminate variables from the test

Propeller pitch: what it is and why it matters

The amount of the spinning drag will be affected by the pitch of the propeller. Pitch is defined by the angle of the blades, and represents the distance forward the prop would move in one revolution assuming no slippage.

A propeller is defined by its pitch (how far the prop travels in one revolution) and diameter

Props with lower pitch generate more torque under power, so they will pick up speed quickly but top speed will be lower, the engine won’t be working hard enough and they create more sailing drag. Props with higher pitch generate more speed under power, so they will pick up speed slower but eventually go faster, the engine may be working too hard but they generate less sailing drag.

As with most things, the choice is a compromise based on performance priorities, engine RPM and gearbox ratio, but a prop for a typical cruising yacht will have a pitch of 10-14in, in which case the drag of a spinning prop will be less than that of a fixed prop.

The test rig worked as we had hoped, and gave remarkably consistent results as the speeds increased. Using the electric motor allowed us to get figures for equal levels of power, which equate to equal wind speeds. The hull speed of our boat restricted us to a maximum speed of 5 knots, but in reality it is at these speeds that the drag of the prop has its greatest effect.

A locked, three-bladed prop generated nearly as much drag as a 10in bucket!

To put these results in context, towing a 10in diameter bucket produced just 10 per cent more drag than locked prop.

Conclusion: ‘Let it spin’

The results show that our spinning three-blade prop creates considerably less drag.

Many gearbox manufacturers have their own restrictions on whether you should lock or spin. Almost all of today’s hydraulic boxes can be safely left to spin in neutral but in the past, some hydraulically-operated boxes had their lubricating oil pumps driven by the input shaft from the engine, so if you left them in neutral under sail, with the engine stopped, they would suffer oil starvation.

On the other hand, some mechanical boxes actually warn you not to lock them in gear when sailing, as the load on the fixed prop can damage the internal components of the box, and even turn the engine over, so you should let them spin. As always, check the specific instructions for the gearbox in your boat before deciding.

Different props and hull shapes

Unsurprisingly, the graphs above show a compelling reason to fit a folding prop if your boat has a saildrive or P-bracket. If you have a long-keel yacht, with a thin-bladed two-blade prop set in an aperture, and you have a mark on the shaft telling you when the blades are vertical, then you will also have minimal drag. But with a fin-keeler, if the prop is behind a P-bracket, there will be little gain in orientating the blades vertically.

The drag of a three-blade prop on a saildrive will be almost identical to our test, as our outboard leg was similar in section to a saildrive, rather than a P-bracket.

How we tested

We mounted the prop on an outboard leg, which had a similar underwater profile to a typical saildrive

We wanted to measure the drag of a 12×12 (12in diameter and 12in pitch) three-bladed prop accurately, first fixed, then spinning, over a range of speeds.

We used a spring balance to measure drag and a weight on the tiller counter-balanced the weight of leg and prop

Then, as a comparison, we measured the drag of a folding prop supplied by Darglow, and finally we towed a bucket behind, to see how much drag that generated.

We measured the current and volts of the electric motor to determine drag and speed loss as power increased

To measure drag, we mounted the props on an outboard motor leg, clamped to the transom of a 14ft skiff. We then powered the skiff with an electric outboard mounted alongside, measuring the current and volts of the motor to determine the reduction in speed caused by drag for a given power – we used electric power, at sea it’s the wind.

In practice, the amount of spinning drag will be increased from the theoretical level, as some force will be needed to overcome the friction in the gearbox. Even in neutral, a gearbox will have some internal drag, but this has less effect on the boat than locking the prop. Our test leg had a gearbox, so it closely replicates the real situation.

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Understanding Your Sailboat Propellers

By Michael Cilenti
Updated: July 6, 2015

Out of sight and out of mind, sailboat propellers are often an afterthought for cruising sailors. Ironically, because manufacturers have developed a variety of efficient sailboat propellers designed to maximize thrust under power while minimizing drag under sail, selecting the right prop for a sailboat can be even more complex than it is for a power vessel. In order to make an informed decision and choose the right propeller for your needs, it’s important to understand the advantages and disadvantages of all the options available.

Propeller Geometry

Before delving into specific types of sailboat propellers, in order to grasp how all the design elements work together, it’s important to understand the basics of propeller geometry. All propellers — from sailboats to power cruisers, outboards to aircraft carriers — share the following characteristics.

To start, the hub is the central part of the propeller, to which its blades are attached either as a single casting or mechanically; it, in turn, is connected to the propeller shaft in traditional drive trains, or to the saildrive , which has become more and more prevalent in contemporary cruising boats. Regarding those blades, the leading edge is just that: the edge that leads into the water when turning ahead. (It’s also the edge closest to the forward part of the propeller hub.) The trailing edge , conversely, is the opposite edge of the blade (the one closest to you when standing on the aft side of the prop).

The root is the inboard side of the blade and forms the transition where the blade connects to the hub, while the tip is the outboard edge of the propeller blade. The blade face is also known as the pressure side, and is the side that faces aft. The blade back is also known as the suction side, and is the side that faces forward.

The majority of propellers are right-handed ; viewed from astern, they rotate clockwise when moving forward, and have a slight tendency to swing the stern to starboard. Since the propeller is designed to be most efficient when going ahead (the direction one travels the vast majority of the time), this side force is minimal. When going astern, however, the opposite is true, and the stern will “walk” to port, which is usually the more pronounced of the two side forces and can therefore be a distinct advantage, or disadvantage, when maneuvering in close quarters. Prop walk is dependent on several factors, including hull shape, but also the propeller itself. An inefficient propeller will introduce more prop walk than an efficient one.

Diameter and pitch are two of the most basic dimensions used to describe a propeller. If you were to attach a pencil to the tip of one of the blades and rotate the propeller one full turn, tracing a circle, the distance across this circle would be the diameter of the propeller. Next, if you were to rotate the propeller one full revolution in a solid medium that does not slip (think of a screw in wood), the pitch would be the forward distance that the propeller would travel in that single revolution. With modestly sized yacht propellers, diameter and pitch are routinely measured in inches (as opposed to feet or meters for ship propellers). So a 12-by-20 prop has a 12-inch diameter and a 20-inch pitch.

Given the definition of pitch, you might wonder why you wouldn’t choose a propeller with higher pitch in order to gain additional power. But propellers must be sized in relation to the rest of the propulsion system, and must match the power curve of the engine, as well as the rpm range afforded by the reduction gear. As such, a propeller with excessive pitch may not actually generate additional thrust, since it would overload the engine and prevent it from reaching the designed rpm, which can reduce fuel efficiency and increase wear to critical engine components. Additionally, an overloaded propeller is susceptible to cavitation , which happens when a prop rotates and creates a partial vacuum. Water rushes in to fill that vacuum, creating tiny bubbles; when they collapse, they basically pound the prop. While cavitation will occur in small amounts in very localized areas on almost every propeller, excessive cavitation will result in a loss of thrust, excessive noise, and vibration, and can be violent enough to actually pit or erode the propeller.

Many blades also have rake and skew . Rake is the forward or aft slant of the blades when viewed from the side. Propellers are generally given some degree of aft rake to help increase efficiency while decreasing vibration. In fact, many propellers on outboard engines exhibit a significant amount of aft rake. A propeller blade is skewed if it is asymmetrical with respect to a straight radial line drawn outward from the hub. Skew helps reduce pressure fluctuation and therefore vibration and noise.

As an example, think of those classic World War II films, when the submariners would huddle together, waiting for the next depth-charge attack while listening to the pulsating sound of the destroyer’s propellers as it passed overhead. That distinct pulsation was caused by the difference in pressure as each propeller blade passed close to the ship’s hull. Even if the propeller blades were equidistant from the hull on all sides (think of a propeller in a tunnel or nozzle), the pressure difference between the propeller tip closest to the surface and the tip that is deepest can be substantial enough, especially in larger propellers, to cause similar pulsation. The prop on a modern submarine is an example of a highly skewed propeller; the sickle-shaped blades are designed to reduce noise and vibration to an absolute minimum, even at the expense of propulsive efficiency.

The number of blades can also play a significant role in the propeller’s performance. As with skew, at least in theory, a greater number of blades will generally reduce vibration, since for a given rpm there is less time between each blade passing a given fixed point. That said, if a propeller is well designed and dynamically balanced, a two-bladed prop will not vibrate more than a three- or four-bladed prop. However, in instances where a shaft is slightly out of alignment, a three-blade prop could help decrease shaft vibrations.

Along these lines, if a propeller had an infinite number of blades — if it were a solid disc — there would be no vibration. Additionally, a propeller with more blades will generally have a larger expanded area than one with fewer blades, although that is not necessarily always the case. Expanded area is essentially the total area of the blades. For a given horsepower, a larger expanded area will result in lower thrust loading, or conversely, a propeller with a larger expanded area can absorb more power prior to experiencing significant cavitation. At the end of the day, it’s a delicate balance between optimum blade area and the potential for excessive diameter. Wide diameter causes excessive tip speed, which results in cavitation.

Propeller Options

There are several propeller types available for auxiliary sailboat applications. To begin, let’s look at some basic but often confused definitions for different types of propellers.

Blades may have constant or variable pitch. A propeller with constant pitch has blades whose pitch, or angle of attack, remains the same from the root to the tip. Conversely, a variable-pitch propeller has blades that appear twisted; that is, the blades will have greater pitch at the root and less pitch at the tip.

While constant-pitch propellers are easier and therefore cheaper to manufacture, variable-pitch blades are more efficient. Consider each blade’s motion as the propeller spins. At a given rpm, the part of the blade near the root is moving much slower than the part near the tip. If this seems confusing, think about the change in circumference as we move outboard on each blade; a point closer to the hub has less distance to travel to complete a full circle than does the tip of the blade. Since they both must complete the revolution at the same time — they are, after all, two points on the same blade — the point near the tip must move faster than the point near the root. Now, we also know that the faster the blade moves, the more thrust it will produce. So, in order to maintain constant thrust along the entire blade, the pitch is reduced as we move farther out toward the tip.

Propellers may also have either fixed pitch or controllable pitch . Fixed props are available in a wide range of diameters and pitches. All fixed props have twisted blades, but as the name suggests, they can’t be adjusted. Feathering props, alternatively, have flat blades with no twist. This makes the blade area relatively inefficient, but that drawback is offset by the ability to adjust the blades’ pitch.

A controllable-pitch propeller also has the ability to change the pitch of the prop blades, by rotating each blade at the root, but these props are generally used on superyachts, not your normal cruising boat. On these larger vessels and ships, controllable-pitch propellers are used to keep the engine operating in the most efficient rpm band by varying the pitch of the propeller to change its thrust rather than the speed of the engine.

Additionally, many controllable-pitch propellers also have reversible pitch: In order to provide astern thrust, the pitch of the propeller blades is reversed while the propeller continues to spin in the same direction. For larger ships, this has some distinct advantages, as it eliminates the need to stop the propeller before turning it in the other direction. This simplifies the machinery required and dramatically reduces the time before reverse thrust is produced, therefore increasing maneuverability. For sailing vessels, in addition to the advantages previously described, controllable-pitch propellers can often “feather” the blades to minimize drag while sailing.

Controllable-pitch props can also be adjusted to maximize the power and efficiency of your particular propulsion system and boat, something that fixed-pitch propellers cannot do. This ability to fine-tune the propeller — coupled with advanced blade designs in controllable-pitch props — may promote a notable increase in power, speed and efficiency. It’s important to note, however, that compared to fixed-pitch models, these controllable-pitch benefits do come at increased cost. Cost aside, the complexity of the system also may make it more prone to issues than a fixed-pitch propeller, and more difficult to find parts and complete repairs when voyaging in remote regions.

Of course, many sailors are familiar with folding propellers, which are fixed-pitch models designed to fold back in order to minimize drag while under sail. Like fixed props, these come in a wide variety of diameters and pitches, have twisted blades, and aren’t adjustable. Originally, folding props were generally two-bladed, but three-bladed props are now widely used and very popular, and four-bladed models are also available. Folding props are designed so the centrifugal force of the spinning shaft will cause the blades to unfold when the engine is engaged. Folding propellers are less complicated than their controllable-pitch cousins, but compared to standard fixed props, they still offer reduced drag under sail. When folded, they are also less prone to being fouled by seaweed or other debris than a feathered, controllable-pitch propeller.

In days gone by, many folding propellers got bad raps for several reasons. They wouldn’t open immediately at low rpm, particularly in reverse, or they required a revved engine to provide the sufficient centrifugal force to open them. Conversely, at low speeds while under sail, the flow of water was sometimes insufficient to keep the blades folded, particularly if the prop blades were aligned top to bottom (where gravity could open the bottom blade) rather than side to side.

When we raced sailboats when I was younger, we used to dive down and put a rubber band around the folded prop once we got out to the racecourse. Or we’d make a mark on the propeller shaft with paint or a permanent marker when the boat was on the hard; we could then position the shaft so the blades were aligned side to side once we secured the engine. However, those issues have largely been eliminated with today’s modern, highly engineered folding props. These days, the blades in most folding props are geared and synchronized, and very efficient in all conditions, whether under sail or motoring. Their reliability is underscored by the fact that they’re now standard equipment on new boats from Beneteau, Dehler, Gunboat, Hanse, J-Boats, Jeanneau, Morris and many other manufacturers.

The variety of propellers available today provides a wide range of options for sailors to choose from. The advantages and disadvantages of each propeller type must be weighed against your sailing and motoring style. When investigating a new prop, shop wisely and ask lots of questions of the specific manufacturers; it’s important to get personalized recommendations for your boat and your plans. Understand the differences to ensure you find the best fit for your needs.

Propeller Resources:

The following is a list of propeller manufacturers and their websites.

Autoprop Automatic Variable-Pitch Propellers
Flexofold Folding Propellers
Gori Folding Propellers
J Prop Feathering Propellers
Kiwiprop Feathering Propellers
Max-Prop Feathering Propellers
Martec, Autostream and Slipstream Folding and Feathering Propellers
Variprop and Variprofile Feathering Propellers
Volvo Penta Folding Propellers

A graduate of the U.S. Coast Guard Academy, where he raced inshore on the varsity sailing squad and offshore to Bermuda and Halifax, Lt. Cdr. Michael Cilenti is currently second-in-command of the Coast Guard cutter Waesche out of Alameda, California .

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Propeller Drag Under Sail Test

Post author By Rick
Post date June 29, 2010
9 Comments on Propeller Drag Under Sail Test

Propellers are a sailboat subject which sometimes turns into extremely heated exchanges when sailors gather and discuss propeller drag under sail. There are two schools of thought, of course. One school says that for best performance, propellers should be locked in reverse when sails are raised, and the engine(s) stopped. The other school of thought says that our transmissions should be put in neutral, and the propeller(s) allowed to free wheel while sailing with the engine off.

This is of particular concern for us cruising catamaran owners as we have two propellers in the water and double the drag. We all know that underwater drag under sail is drag we can do without. So, which school of thought is correct? Hint …you don’t have Helicopter rotors on a boat.

I have never seen so much misinformation on a sailing subject tossed around the sailing forums as there is on propeller drag. I recommend you read this page carefully, as there’s no hidden agenda here. This page exists because it’s important for all of us to get this right.

First, a note on Marine Diesel Engine transmissions

Concerning Yanmar diesels, there’s solid information from Yanmar on this subject. In Yanmar Advisory Number: MSA08-003 Dated: February 8, 2008 and sent to all Marine Distributors, they state that Yanmar requires their transmission be kept in neutral while sailing. In fact, they warn of internal damage to the gear or sail-drive which will result if the Yanmar transmission is locked while sailing, and that this damage will not be covered by Yanmar’s Limited Warranty. This advisory points to another which states the identical policy for sail drive units. This is an advisory which pretty much ends the debate on whether or not to free wheel propellers while under sail with Yanmar diesels installed… don’t you think?

Read the Yanmar Advisory But wait there’s more. Volvo has also addressed where their transmission should be when sailing. They also say the transmission should be put in neutral during sailing. If you ignore this, you’ll be buying new transmissions regularly.

Read the Volvo instruction manual (page 21) Volvo and Yanmar diesel engines probably represent 90% of diesel engines found in sailboats. So, for 90% of the sailing community the issue of where your gear shift lever should be when sailing has already been decided. If people don’t have one of these engines, they should look to their owner’s manual on their transmissions, but engine manufacturers like Yanmar and Volvo actually require their transmissions to be put into neutral under sail or the engine warranties are invalid.

Unless your transmission specifically says to shift into reverse while sailing, all sailboat owners should be free wheeling their propellers while sailing.

Now …. we know where the transmission should be set when sailing … but … RC of Sailnet.com , better known as “Maine Sail” decided to find out if locking the transmission hurt his sailing performance by increasing underwater drag, or if freewheeling the propeller reduced drag and was actually faster. This test has put an end to the bickering and has done what I feel is the definitive work on this subject. He has graciously allowed me to reproduce his work on this page.

This is the first comparison I’ve read between free wheeling propellers and fixed propellers that has an accompanying video verifying each phase of the testing procedure, as well as photos illustrating the jig constructed for the test. Also, it should be mentioned that this test was done in a harbor, not a test tank and the results are both conclusive and inescapable. Scroll down the page a bit to view the video of the actual propeller test.

Now, on to his test…

Maine Sail’s Propeller Drag Test (with his permission!!)

Over last winter there were a few discussion on sailing forums that although entertaining, lead to no hard conclusions on whether a fixed prop or a locked prop causes more drag while under sail. There have been two studies that have both concluded that a freewheeling prop causes less drag but these studies were done in test tanks and some sailors argued that vortexes created within the tanks throw off the results.

I don’t like not knowing.

I spent a few late nights in the barn, over the winter, listening to good tunes and plugging away on a way to test the theories and came up with a test rig. This jig told me what I needed to know. It was designed to be affixed off the side of my dinghy and dragged through the water ahead of the motor, to avoid vortexes & whirligigs and what ever else, and at a depth similar to that of my own sailboats fixed prop.

Propeller Drag test

I obtained drag test results with both a locked propeller and a freewheeling propeller as well as measuring the drag of the jig alone, (which was 12 lbs). The jig drag was subtracted from the actual drag test results of both the locked propellers and the freewheeling propellers, to arrive at a net difference in the test.

I designed the jig bearings to have a similar resistance to the prop shaft on my own sail boat so from that perspective all is quite comparable in terms of freewheeling.

The propeller drag measurements were captured with a 50 Lb. analog scale (I had to ditch the digital scale shown in the photos as analog showed better on video) and GPS was used to measure SOG so as to more accurately compare between the same propeller in both fixed and freewheeling modes. The range of motion on the scale (movement of the hook) from 0-50 lbs. is about 1/8 inch so this did not affect any readings what so ever by changing the angle of the test jig in the water..

The propeller I used is a standard three blade fixed sailboat prop. It is made by Michigan Wheel. So this post focuses on the Michigan Wheel three blade prop which is perhaps the most common fixed prop used on sailboats in the US.

This is an age old argument, which can be resolved with a relatively easy test, yet surprisingly no one has done it, not even Practical Sailor.

The results of the Michigan Wheel MP propeller were…well surprising to say the least. I want to clarify some points below so there is less confusion.

1) This test was only to determine if a standard Michigan Wheel three blade fixed prop causes more or less drag when towed through the ocean at a similar depth to that of a sailboat, particularly my CS-36, and with a comparable shaft resistance to a sailboat (namely mine). It is not to give accurate numbers or data on how much drag the specific prop creates.

2) Drag is relative to the the drag jig I used. The drag jig alone, with no propeller attached, created about 12 lbs. of drag in this configuration at WOT (wide open throttle) on my 4 hp Johnson outboard.

3) Because the test jig is exactly the same in both fixed and freewheeling tests and the ONLY difference between the fixed propeller and the freewheeling propeller test was a 2.5 inch roofing nail, I can definitively state that the only differences in the propeller drag tests comes from the propeller not being able to spin and spinning.

4) The motor was always run up to wide open throttle to totally minimize any throttle position variability between the propeller being locked or freewheeling.

5) The pin point accuracy of the scale means little because it is only a control. The same scale was used for both fixed and freewheeling and it was only compared to itself in an A/B situation, fixed/freewheel.

6) The difference between the fixed and freewheeling tests was LARGE , so a pound or two here or there means very, very little. The test jig measured the average drag at WOT (wide open throttle) in freewheeling mode, including the strut, at 20-25 pounds. The average drag in fixed (locked) mode, including the strut, was about 45-50 pounds.

As you can see .001 differences in accuracy do not matter when trying to answer this question as related to this very, very popular sailboat prop.

For those worried about whirly gigs and vortexes and .0001 differences I then turned the test jig around, with the propeller facing forward, and ahead of the struts “interference wake”, and reran the test. I was surprised that I could not detect a discernible difference in load despite having to move the line a little higher on the strut. If there was a difference it was clearly less than one or two pounds and not noticeable in the big scheme of things.

7) Freewheeling is little bit of a misnomer. The shaft was not actually allowed to freewheel with minimal to no friction. The friction bearings I designed were tightened and adjusted to closely mimic the friction of my own sailboats shaft. This test was primarily for me and my own curiosity and then secondarily for the sailing community. This is why the depth of the prop in the water matches my CS-36T and the shaft friction was set to begin spinning at about .8 – 1.2 knots which is what it does on my own boat.

8) The results for the Michigan three blade prop are quite clear, and quite discernible, and coincide with those of the MIT study, the University of Strathclyde study and other prop drag tests like the one in a the UK’s Yachting Monthly magazine.

9) This experiment & video below is about the prop used, a Michigan Wheel three blade “MP” prop. I make NO claims or suggestions about any other fixed type props including a two blade version of the Michigan Wheel MP. If someone wants to send me a two blade MP in a 1″ shaft size I will be glad to test it too..

10) As far as I know this the ONLY video proof that clearly shows a fixed vs. freewheeling three blade sailboat prop being load tested and compared only to itself in both fixed and locked mode.

11) Before anyone gets all fired up because they are a believer that fixed three blade props cause less drag, not more, PLEASE remember that the ONLY difference between the fixed and freewheeling modes was a 2.5″ nail passing through both the jig and the 1″ shaft to lock it in place. There is NO possible way that 2.5″ nail caused a nearly 300% difference in drag or a 25 additional pounds of resistance.

12) I need a bigger motor! I was only able to attain a max speed of about 4.2 knots with the jig and prop in the water freewheeling and less in locked mode. I’d like to hit 6.5-7. Most sailors though are concerned about prop drag at less than hull speed and the 4 knot range is less than hull speed for most sailors. In light winds, and under hull speed, with a fixed three blade Michigan Wheel, you will see less drag when freewheeling!

Propeller Drag Test Results

Total Jig Drag = measured 12 pounds with no propeller mounted. Jig drag measurement was taken at WOT. (wide open throttle)

Locked Prop Drag = 45-50 pounds: When we subtract the measured jig drag, 50-12 = 38 pounds measured of actual propeller drag when locking the propeller in reverse under sail.

Freewheeling Prop Drag = 20-25 pounds: 25 – 12 = 13 pounds of actual propeller drag when freewheeling the propeller under sail.

The locked propeller drag is 2.92 times more drag or a 192% increase in drag over a freewheeling propeller when you remove the test jig from the equation!!!!

As I said earlier, the test results are not even close. There’s no need to worry about the .001’s or a few pounds of drag here or there or even the rather “unscientific” method I used in this test. If a sailor cares to find an additional knot of boat speed in light winds, he must free wheel his propeller under sail. (note: I picked an average wind day with flat water and tried my props both locked and free wheeling while under sail. I have two props on my catamaran, and Main Sail’s test was verified on my boat (it wasn’t even close) -end of test data-Rick)

Despite the Yamar advisory, which voids their warrantee if you lock their transmissions while sailing and despite Volvo’s recommendation that you sail while their transmission are in neutral and despite the MIT study, the University of Strathclyde Ocean Engineering white paper, the Yachting Monthly data and this webpage, which all show the same thing, that a locked propeller creates more drag when under sail , there are still a few Forum “expert” types arguing the helicopter blade theory. Which kinds of makes me wonder how many of these forum “experts” actually own a boat…..

I’ll repeat that I’ve never seen as much misinformation on a sailing subject as we get on propeller drag under sail.

Supporting Documentation

Now that you’ve read the warnings and understand that most sailboat owners should be free wheeling their propellers while sailing. What’s more …. ‘Main Sail’s’ test positively demonstates that your boat is faster with the transmission in neutral.

Since it was mentioned, I’m posting a link to both the original MIT paper on the same subject and The Sailboat propeller drag paper written by P.M. MacKenzie and M.A. Forrester below this paragraph. They are with the Department of Mechanical Engineering, University of Strathclyde, Glasgow , Scotland. The MIT report is an in depth study of 10 Propellers from many manufacturers and both fixed 2 and 3 blade as well as Maxi props. Actually, both papers are interesting reading and you would have thought these papers would have ended the controversy. In fact every study which was ever done on this subject has come to the same conclusion, a locked propeller creates more drag when under sail , yet that hasn’t even slowed down all the misinformation being dished out in sailing forums by ‘arm chair’ sailors.

I’m hoping that our very own “Maine Sail’s” work can do what MIT and the University of Strathclyde could not. Educate sailors and dispel old wives tails and actually change the thinking in the sailing community to understanding that Free Wheeling a propeller instead of locking props under sail is better whenever it’s appropriate.

MIT Propeller Report

University of Strathclyde Propeller Report

One final note on this subject. We have to mention Prop Feathering. The helicopter blade theory cited by some arm chair sailors does have a basis in fact. If you are able to reduce the pitch of a propeller to zero and actually feather the prop, as you can on an aircraft, … you will achieve very low drag. For almost all of the sailing world this is irrelevant trivia as very few boat owners can justify the expense of adjustable pitch propellers (do people really spend $2500 on a single propeller???) I would call sailboat Prop Feathering with an adjustable pitch propeller a red herring. Although it’s the perfect solution to reducing prop drag, it simply doesn’t apply to more than 99% of sailboats affected.

This webpage has been mentioned as the best propeller drag comparison test on the internet and the only place all the propeller drag tests can be found in one place. I will humbly point out that apparently Michigan Wheel Marine (propeller manufacturer) feels this way as they have cited this webpage as the definitive resource on the subject ( link to their page ).

A huge “Thank You” to Maine Sail for the time and trouble he devoted to answering this question once and for all and for allowing his test to be published on catamaransite.com , a resource for catamarans for sale by owner .

Tags Buying Advice

Owner of a Catalac 8M and Catamaransite webmaster.

9 replies on “Propeller Drag Under Sail Test”

Eric Hiscock locked the prop with two blades as he described using Wanderer 4. He locked it vertically, hidden somewhat behind the keel. I wonder what the comparison would be under those conditions. I understand he locked the shaft, not the transmission. I would love to get remarks, please disclose my email

Frank. If you have a Yanmar, or a Volvo marine diesel, you sail with the engine in neutral because the diesel manufacturers tell you to. And it’s faster…

2.92 times more drag is actually 192% more, not 292%. Remember that a factor of 2 times increase is a 100% increase because the percentage is relative to the base number. This is, unfortunately, a common error in citing percentages greater than 100 or more.

The Yanmar and Volvo directives make me wonder what harm could come to those engines from leaving them in gear while sailing? They say to leave it neutral or get a shaft lock. Hmmm. Must have something to do with vibration backfeeding into the engine.

My understanding is it wears out the transmissions.

It is likely that the transmissions are not properly lubricated when driven from the output shaft while in neutral. Many transmissions are lubricated by the gears on the transmission input side, not the output side. This is why you see most vehicles (cars) being flat towed behind motorhomes are vehicles that have a transfer case. This is also why tow trucks tow vehicles with the drive axle no spinning.

If Yanmar and Volvo (and Lombardini marine for LDW 502 M, LDW 702 M, LDW 1003 M, LDW 1404 at https://www.deltaservicedieselengines.com/img/manuals/Focs_Manual_IT_EN_FR_DE_ES_PT.pdf ) advise or require running in neutral (unless you have folding or feathering prop, where reverse is advised), the problem greater than gearbox wear might be that the prop could be rotating the cold engine when not powered on, but didn’t see any explicit answer on that. I have also seen reported: “Our Volvo manual albeit a 2040 says don’t put in gear and to run the engine every 10 hours of sailing. If that’s not an option fit a shaft brake. “, but didn’t see that manual yet. That is a no-brainer if you allways overnight in a port or a marina and approach and exit on engine, but might be a problem if you a long ocean passage, and you could need a brake (or better folding prop). I didn’t yet see what should be the exact reason for that reported Volvo piece of advice. About drag: Beneteau Oceanis 41,1 went about 4.5 kts with gear locked in reverse and about 6.5 kts with the same sail and boat configuration and weather situation when I got awake and put gear to spin in neutral. The guy that put it in reverse has a folding prop on his own boat and didn’t see the difference he had caused during night shift of sailing. Instruction leaflet for engine and gearbox for that Beneteau instructs neutral or reverse for folding, but no reason for that. I also couldn’t find that manual online yet to let you check there.

This was a great read and very helpful. Many thanks for all the effort that went into getting it this far. It has always seemed logical to me that a free wheeling prop would be less drag, confirmation is nice.

Thanks for the positive feedback. We are working on additional articles. If you have topic you would like us to cover, send in a message anytime.

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.

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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Max-Prop Automatic Feathering Propellers

Proven Cruising and Racing Propellers Since 1972

Max-Prop has led the low drag propeller market for 40 years and is still the leader today. Since starting production in the 1970's Max-Prop has proven itself on racing and cruising boats around the world. With over 50,000 propellers in the water, the Max-Prop is tested daily in the harshest conditions and has established itself as the most efficient and reliable low drag propeller.

The combination of low drag, outstanding reverse power, efficient forward performance, and fail-safe design makes Max-Prop the ideal sailboat propeller on the market today. Now with the recent introduction of the Whisper, and the Boomerang models, Max-Prop has taken a further lead over the competition in the propulsion of sailboats.

Max-Prop Models

2, 3 and 4 Blade

For Racers to Large Cruising Boats

Max-Prop Easy SailDrive feathering boat propeller

Easy for SailDrive

For Volvo, Yanmar, TwinDisc, ZF, Sillette or Bukh SailDrives

Max-Prop Whisper feathering boat propeller

For Heavy Displacement Large Cruising Yachts

Max-Prop Boomerang feathering boat propeller

For Larger Vessels with Electronic Shift Transmissions and High Sailing Speeds

Features of a Max-Prop

Under sail, a Max-Prop will increase sailing speed between 10% to 15% in average wind conditions compared to a fixed blade propeller, with an ever-larger difference being given when sailing in light air. The drag under sail varies widely between propellers, number of blades, angle of the shaft as well as location of the propeller on the boat. It is fair to say that a 2 blade Max-Prop propeller located on a horizontal shaft (sail-drive) will have the least drag while a 5 blade Max-Prop on a high angle shaft will have the most drag. However, even a 5 blade Max-Prop on a high angle shaft will have substantially less drag and provide more power when motoring than a fixed 2 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

Max-Props are feathering propellers, so unlike folding propellers, Max-Props do not rely on centrifugal force to open. Instead, the Max-Prop relies on the torque from the shaft rotation acting on the differential type gear design in the body of the propeller. This in turns ensures an immediate opening in forward and more importantly in reverse, unlike folding propellers which have a lag time in reverse.

VERSATILITY

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

INSTALLATION & MAINTENANCE

The Max-Prop will fit directly onto your existing shaft with the boat in or out of the water. The Max-Prop will be matched to your specific shaft taper or SailDrive Spline. The only required maintenance is to grease the propeller once a year, and to replace anodes when they erode away.

Worldwide, many of the top racing boats have opted for the Max-Prop solution.

The three, four or five blade Max-Prop is the propeller of choice for the cruising sailor. The combination of low drag, great performance in forward, increased speed under sail, outstanding backing power, safety and maneuvering, and fail-safe design makes the Max-Prop the ideal cruising propeller.

Advantages of a Max-Prop

Under Sail...

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 .

In Forward...

While not always exactly as efficient as a perfectly sized fixed propeller, a good choice of Max-Prop diameter, pitch and number of blades will usually achieve 96% or better efficiency compared to a fixed blade propeller. This maximum of 4% drop in efficiency is only seen at maximum throttle, which is seldom, if ever, used. The fact that with a Max-Prop, a boat owner or a designer can choose not only the diameter and number of blades of the propeller but can also adjust the pitch easily after sea trials makes the Max-Prop an ideal tool to fine tune a boat’s performance under power.

In Reverse...

The simple fact that the Max-Prop blades use the same leading edge and pitch in reverse as in forward results in an identical power in both directions. A fixed blade propeller looses almost 50% of its power in reverse. Worse yet - a folding propeller which, depending on the brand, can loose up to 80% of its power in reverse. The Max-Prop blades switch from forward to reverse instantaneously. It takes only 3/4 of the shaft rotation for the blade switch to occur.

"WOW! I tested it out yesterday and this new Max Prop is like night and day! It feels like I finally found the "brakes" on the boat. I should have done this years ago!! Backing up is immediate (instead of the usual almost 2 second delay), I have better control in reverse, AND so much more power going forward! Plus my boat vibrates a lot less."

Disadvantage of Folding Props

A folding propeller disadvantage under sail

A folding propeller has low drag. The drag is directly proportional to the projected area: A .

A folding propeller disadvantage in forward

The blades will "slam" open and, if not perfectly aligned or true to each other, will cause vibration.

A folding propeller disadvantage in reverse

In that the blades will not open to the maximum diameter (and occasionally not at all), the reverse power is very poor (much less than a fixed blade prop).

Disadvantage of Fixed Blade Props

A fixed blade propeller disadvantage under sail

A fixed blade propeller includes a tremendous amount of drag, reducing the boats speed an average of 15%.

A fixed blade propeller disadvantage in forward

Fixed blade propellers provide maximum efficiency as long as the pitch is correct.

A fixed blade propeller disadvantage in reverse

A fixed blade propeller works with the trailing edge as a leading edge, reducing its efficiency by 50%.

Max-Prop Propellers For Catamarans

Catamarans are different from monohull sailboats under sail and power. Because of this, the advantages of the Max-Prop are accentuated on a Catamaran. The reduced drag under sail not only improves boat speed but also reduces turbulence over the rudders providing improved boat handling. This reduction in drag also allows a boat to come through a tack quicker and with more boat speed exiting the maneuver, making it easier to sail in light winds.

With the increased beam and freeboard of a catamaran comes the downside of more windage. The impressive reverse power of the Max-Prop adds to the control and safety of the vessel when maneuvering. Max-Prop has propellers for both SailDrive and Shaft driven applications in 2, 3, 4, or 5 blade designs. This allows the boat owner to pick the correct propeller for how they use their catamaran with little compromise.

Features specific to Max-Prop on Catamarans

Improves control and safety of the vessel
Very low drag under sail
Reduced turbulence over rudders under sail
Improved tacking speed with reduced drag
Overcome windage inherent to Catamarans
80% more power in reverse compared to a fixed propeller
Models designed specifically for SailDrive
Adjustable pitch to optimize powering performance
Versatility of blade number

Max- Prop was designed and built in the early 1970’s by Maximillian Bianchi in Milan, Italy. Max, a young Italian engineer invented a new type of propeller at the request of a sailboat racing friend in the golden days of the IOR racing rules. Little did he know at the time, this simple product would become his lifelong passion and livelihood. To this day, Max still oversees any new development of the product and follows it all the way through the manufacturing process. It is hard to believe, but Max quality checks each and every propeller that comes out of his factory. Nowadays, his son and daughter work with him so the legacy will continue long after Max retires (if he ever does).

The Foundry

In order to keep the metal quality to a constant high standard, Max bought a foundry in the mid 70's. To this day, the majority of Max-Prop cast parts are made in that foundry close to Lake Cuomo, a two hour drive from Milan.

The ownership of this foundry not only resulted in high quality cast parts, but also insured that any defect in the material or the part would not be passed on to the next stage of machining. This vertical integration is one of the main reasons for the success and durability of Max-Prop.

The Machine shop

The actual machining of the propellers has always been under the full supervision of Max, from the days of manual lathes and mills to the ultra-modern CNC machines of today. Through the years, the machine shop has had multiple locations and currently is in Milan, in the same building as the sales offices, management and where the final assembly of the Max-Prop occurs. Once again, Max himself oversees each and every process.

Sales Office

PYI is the only sales office for Max-Prop in North/South America and Asia. PYI was established in 1981 and on that date Max-Prop was already the main product distributed. Since then, PYI has added products which are well known in the sailing community, some as a manufacturer and some as a distributor. Through the years, Max-Prop has been the driving force for PYI, allowing us to facilitate the manufacturing of other quality products.

Max-Prop Through The Years

An evolution towards perfection!

Maximilian Bianchi Circa 1972

Maximilian Bianchi Circa 2018

Max-Prop Videos

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.

Catalogs & Price Lists

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Max-Prop Installation Instructions

Max-Prop Classic 2 Blade Installation Instructions
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Yacht Cruising Lifestyle

Everything fun you can do from your yacht

How to Choose the Right Sailboat Propeller

November 10, 2021 by Martin Parker 1 Comment

Introduction

Choosing the right sailboat propeller for your needs is a complex process. Make the wrong decision, and you could end up with an underpowered boat or a constantly over-revving engine. Get the right propeller, though, and your engine will run more efficiently and with less vibration, ultimately allowing for more comfortable cruising.

By understanding propeller basics and seeking the advice of professionals, you can easily find the right propeller for your sailboat. Below, we explain the basics so that you know what to look for when buying your next sailboat propeller. We’ll also take a deep dive into the choices of propellers available for purchase.

Propeller Basics

Propeller on a sailboat out of the water

Before we jump into the more technical details of propellers, it’s essential that you know the basic parts of a sailboat propeller and what they do. Understanding the basics will help you choose the right propeller and give you some knowledge when speaking to the experts.

The hub serves two purposes. First, it connects the propeller to the driveshaft, allowing the engine to turn the propeller and drive the boat forward. Second, the blades are attached to the hub, either as a one-piece casting or using some mechanical means.

There are three terms relating to the blades.

Root: The point where the blade attaches to the hub.

Leading-Edge: When rotating, the blade edge cutting through the water is the leading edge, while the opposite side of the blade is the trailing edge.

Tip: The furthest end of the blade from the hub.

Basic Dimensions

Two measurements define the basic propeller dimensions, the diameter and the pitch, and propellers are described in terms of their pitch and diameter.

The size of the circle made by a rotating propeller. Imagine attaching a marker to the end of a blade and then spinning the propeller one full rotation, with the marker drawing a circle on a piece of card. Measure the distance across the circle, and that is the propeller’s diameter.

The distance the propeller would move forward during a single rotation. Think of a nut and bolt. The pitch of the bolt’s thread is equivalent to that of the propeller. When you rotate the nut through a single rotation, it moves forward a set distance. The distance moved is the pitch, measured in inches.

Sailboat Propeller Sizing

Both diameter and pitch are measured in inches, and the values describe the prop size. A 14/22 prop has a diameter of 14 inches and a pitch of 22 inches. While these dimensions will give you a reasonable propeller size for your boat, other factors also affect the correct values for your propeller.

Your Propeller Choices

When you are considering a new propeller, you have a significant number of choices to make. Some may be forced on you by budget constraints. Others you may deem essential regardless of cost.

Constant or Variable Pitch

The pitch is the blade’s angle of attack through the water, and blades either have constant or variable pitch. A constant pitch blade has the same pitch from root to tip, whereas the pitch of a variable pitch blade reduces towards the tip. When you look at it, a variable pitch blade twists from the hub to the tip.

If your budget is tight, you may opt for a constant pitch prop, as they are cheaper to manufacture. However, a variable pitch prop offers better efficiency and is generally the better choice.

To understand why variable pitch is more efficient, we need to look at propeller speed. As your propeller spins at a constant engine rpm, the hub turns much more slowly than the tip of the blade. Increasing propeller speed equals increased thrust, so to maintain constant thrust along the blade, the pitch reduces towards the tip.

Fixed or Controllable Pitch

Fixed propellers all have twisted blades giving a variable pitch along the blade, but the pitch cannot be adjusted as the name suggests. This makes them cheaper to produce than variable pitch props.

A variable pitch prop allows the blades to be rotated at the root, allowing you to set the correct pitch for varying conditions. Because of the increased cost and complexity, variable pitch blades are rarely seen on cruising yachts and are primarily used on superyachts. There are several advantages that you may consider worth the extra cost;

– Your engine rpm can be set at the most economical speed, with thrust controlled by varying the pitch.

– You may be able to reverse the pitch of your propeller, which is very useful when maneuvering. This eliminates the need to stop the propeller from spinning before changing its direction.

– A variable-pitch propeller can be fine-tuned to get the best efficiency, power, and speed from your propulsion system, something you cannot do with a fixed pitch prop.

– Variable pitch propellers can often be feathered. The reduced drag and therefore reduced fuel consumption offered by a feathered prop may go some way to offsetting the initial cost.

Feathering Propellers

A feathering propeller is a direct replacement for a fixed propeller but with the advantage of less drag when you’re sailing. Once under sail, the prop automatically aligns the blades with the direction of travel, removing the drag caused by a fixed prop. The only disadvantage is that the blades are flat with a constant pitch. This type of propeller is a cheaper alternative to a controllable pitch prop, although with fewer features.

Folding Propellers

If you’re looking for more sailing efficiency, a folding propeller is a common choice. It’s a straightforward design, using the force of the water over the blades to close them flat when sailing. The centrifugal force opens the blades when the prop is turning.

There are some downsides to increased sailing efficiency, though;

– They are only available as fixed pitch propellers.

– Older designs don’t always open with low engine rpm or may only partially open. You may need to rev the engine to open the blades.

– The water pressure may not always be sufficient to push the blades back at low sailing speeds, negating any potential advantage.

– Very poor reverse thrust.

Number of Blades

Older designs were only available with two blades, but nowadays, three and four-blade versions are available. Many of the issues listed above have been addressed with the more modern designs, such as gearing to ensure all the blades open together.

Saildrives are an interesting development with propellers, providing a more compact propulsion system for sailing yachts. Many of the same choices for conventional propeller drive systems apply to saildrives, and you can use all the different propeller types mentioned above.

The primary difference is that the saildrive setup moves the propeller almost directly under the engine, which means the propeller’s angle of attack is parallel to the water’s surface.

Compared to a conventional engine and driveshaft system, these factors will influence the pitch, diameter, and type of propeller you choose.

Sailboat Propeller Issues

Most propellers rotate clockwise when moving forward. Prop walk is the sideways force generated by the spinning propeller, but it’s barely noticeable moving forward.

Going astern is a different prospect, and you can usually feel a distinct movement of the stern to port. You can counter the effect with the rudder, but you can also use it to your advantage when maneuvering.

Propeller design can also contribute to the amount of prop walk you experience.

Cavitation happens when the prop becomes overloaded, and a vacuum forms around the blades. The effect of water rushing into the vacuum creates tiny bubbles, causing a loss of thrust, vibration, and noise. Excessive cavitation can even damage the propeller. Your propeller’s design and the shape of the boat hull can significantly impact how susceptible the propeller is to cavitation, so it is essential to get it right.

Ventilation

Often confused with cavitation, ventilation is the result of the propeller drawing in air. There may be a design fault when propellers sit too close to the surface, but problems can also arise when the propeller spins too fast.

Factors Affecting Your Choice Of Sailboat Propeller

Engine power

It’s crucial to choose the right size prop for your engine. If your propeller is too large or over-propped, then the engine will struggle to reach maximum rpm. When a propeller is too small or under-propped, your engine will rev out too quickly.

When looking at prop size, you must also factor in any gearing in the drivetrain. The gearbox supplies the power output from the engine, so it’s the output shaft torque and power figures that are important.

Hull Resistance

The wet surface of your hull produces resistance, but of course, you also need to factor in any drag caused by extra protrusions on your hull. This will include the rudder, driveshaft brackets, speed sensors, depth sounder, etc.

Choosing The Right Propeller For You.

Many factors affect your choice of a propeller, and no one solution is better than the other. The first consideration is your motoring requirements, followed by your budget restraints.

If your budget is tight and you only occasionally use the motor, a fixed blade prop is probably your best choice.

Alternatively, a folding or feathering prop could be the best choice if you want to maximize your sailing speed, reducing drag.

When maneuverability is the priority, a feathering prop might be the right choice.

While the options above relate to specific uses, the main characteristics of a propeller are pitch and diameter. These define how the prop will perform and should be the starting point for any propeller choice. Once you determine these basic choices, you can consider more technical factors.

FAQ’s

Is A Bigger Sailboat Propeller Better Than A Small Propeller?

Is bigger better? No, not always, and in the case of propellers, going bigger could cause you all kinds of problems. In terms of size, we’re talking about the diameter of your propeller. A larger diameter propeller will give you more blade area and give you more thrust – in theory.

However, if your propeller is too big, the engine will struggle to turn it and never let it get to its optimum rev range. An oversize propeller will restrict your boat’s performance and increase your overall fuel consumption.

Should You Choose The Highest Pitch Propeller For More Speed?

This is a similar consideration to that of the size (diameter) of your propeller. Increasing the pitch of your propeller blades should, in theory, give you more thrust. As with the diameter, though, too much pitch will limit the performance.

Does A Bigger Propeller Mean Your Boat Will Go Faster?

No, and it may make your boat slower. As we discussed throughout this article, choosing the correct propeller involves numerous factors, and it’s not a simple question of size.

What Factors Should You Consider When Choosing a Propeller?

The first and most important factor is how you sail your boat and how often you use your engine. If you tend to cruise gently, using your engine only when there are light breezes, then low vibration and low cost are possible priorities.

Anyone who enjoys racing will look for speed and low drag, so a folding or feathering prop will be a priority.

Need more advice on buying a sailboat propeller? Get a conversation started on our forum by leaving a question or comment!

If you found this article helpful, please leave a comment below, share it on social media, and subscribe to our email list., for direct questions and comments, shoot me an email at [email protected].

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Reader Interactions

July 28, 2022 at 1:24 am

First of all, your first prop size numbers are reversed. In almost all sailboat application propellers the diameter number is larger than the pitch number. 22D x 14P , for example is more along the ratio of diameter to pitch, for the reason of motor H.P. in relation to Tons of boat which you need to propel. The only applications, which are few, where you would run a prop with a higher pitch number than Diameter is when your transmission ratio is aprox. 2 or 2.5 -1, thus a slower turning prop shaft.. l am a prop shop operator in Cancun.. Thank You..

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Sailboat Propeller

Which Type of Sailboat Propeller is Right for Your Boat?

What we'd really like is a sailboat propeller that's 100% efficient under power with zero drag under sail. Of course, that's never going to be possible but we can get some way towards it.

It would be nice to think we sailors only use our engines for getting in and out of harbour and topping up the batteries.

But when the wind is being uncooperative - not enough of it, or blowing from where we want to go - then many cruisers will drop the headsail and motor-sail towards their destination.

The point at which we do so is a personal decision. Some of us only resort to it after the spinnaker has collapsed lifeless and deflated onto the foredeck, whilst others cheerfully turn on the donk if they can't fetch their destination on one tack, or get ashore before the bars close.

Skippers of older yachts with single cylinder long-stroke thumpers may be more reluctant to do so than those with modern high-revving but quieter, vibration-free installations - but sooner or later even they will be reaching for the ignition keys.

Fixed-Bladed Sailboat Propeller

And having made the decision to motor you might as well get a move on, and a fixed three-bladed propeller is the one to have for performance under power.

Ah, but what about the drag it creates when under sail?

Good point, the drag created by a fixed three-bladed prop is akin to towing a bucket, although the drag of a fixed twin-bladed prop can be reduced somewhat by lining it up vertically so that it's in the disturbed water aft of the keel.

Under sail, and with the engine off, popular opinion tells us it's best to put the engine in gear as a non-turning propeller will create less drag than one which is spinning freely.

If you're at all interested in performance under sail, there's little option but to spring for either a folding or a feathering sailboat propeller. Unless that is, you have opted for a shaft driven generator to top up the batteries; if so a folding or feathering prop isn't an option.

In light airs one of these low-drag props can offer a dramatic increase in speed under sail, typically around half to a full knot - maybe 1.5 knots in light airs. They're not cheap, but usually represent the best performance gain per dollar when considered against other possible speed-seeking expenditure on rig or sail modifications.

Folding Sailboat Propeller

Folded 2 bladed sailboat propeller on saildrive leg

A 2 bladed folding prop is shown here on a saildrive unit, but 3 bladed versions are also available.

On both types, the blades are pivoted and fold backwards under the force of the water flow when not being driven by the engine.

It's often necessary to put the engine in gear to stop the shaft from turning which will get the blades to close.

Very low drag characteristics;
When folded, won't get hooked up on ropes or other floating flotsam and jetsam;
Simpler design, hence lower purchase price than the feathering type.

Disadvantages

Astern performance compromised due to the centrifugal force required to hold the blades open being opposed by the thrust of the blades pulling the boat astern;
Tendency to wear quicker than feathering type;
Pitch of the blades is fixed.

Feathering Sailboat Propeller

feathering 3 bladed sailboat propeller on saildrive leg

An internal mechanism turns the blade's edge into the water flow to minimize drag when under sail, as shown here.

As engine power is applied the blades are turned into the required position for forward or reverse propulsion.

Most feathering propellers have a pitch adjustment mechanism that allows adjustment of the propeller to the optimum pitch for the vessel.

Some feature external pitch adjusters, which give simple access to the adjustment for forward and reverse independently.

Forward can be set for optimum motoring performance and reverse can be set for best maneuverability and thrust - handy when trying to back off a sandbank, or bringing the boat to a rapid stop.

Adjustable pitch offers optimum performance both forward and astern;
Much lower drag than a fixed prop;
More robust construction than a folding prop.
High price;
Slightly more drag than a folding prop;
More likely to foul ropes or nets when feathered.

fixed or feathering sailboat propeller in skeg rudder aperture

Sailboat Propellers in Apertures

Long-keel boats and some fin and skeg arrangements (like the one shown here) where the propeller is located in an aperture are unlikely to have room for a folding prop; a fixed or feathering propeller is the only option in this situation.

And whichever type of sailboat propeller you choose, a rope cutter fitted just forward of it may well turn out to be a wise investment.

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How to Choose a Boat Propeller That Won’t Drag You Down

If you own a boat, chances are it has a propeller. Well, unless you're tacking, jibing and hoisting sails , that is.

You wouldn't think there was much to a prop. After all it's a piece of metal with a couple of blades on it, right? Well, no. Though seemingly unobtrusive (it does spend most of its time under the water) piece of metal actually has quite a lot to do with the performance and fuel efficiency of your boat .

You might be surprised by all of the different technical terms that go into boat propellers. I know I was. It's so much more than a spinning piece of metal hanging onto the bottom of your boat's engine (or a decorative touch on the trailer hitch on the car in front of you in the drive-through).

How to Choose a Boat Propeller That Won't Drag You Down

Features of boat propellers.

When you think about all of the words that describe boat propeller - words like slip, rotation, cup and skew - it sounds like something out of a baseball game. Before you call a ref to intervene, check out these things you should know about choosing the best boat propeller.

The blades are probably the most obvious part of the propeller. They're the things that spin and propel your boat forward. They're also the things you have to watch out for when swimming around the back of the boat while anchored out , but that's a different topic altogether.

Number of Blades

Two Blades: Two-bladed boat propellers are made for smaller boats and smaller motors. They provide quiet and gentle power. These are usually the propellers you'll find on trolling motors.

Three Blades: Three-bladed propellers are the most common type. They're usually made out of aluminum and are less expensive to produce. Being that fewer blades means less drag, this allows for faster speeds. However, this can also cause more vibration.

Four Blades: Four-bladed props are also fairly common. They're usually made of stainless steel, making them strong and durable. Four blades are good for rough conditions and offer great fuel efficiency.

Five and Six Blades: As with most anything, the more parts there are, the more expensive the item is going to be. Five and six-bladed props are the most expensive to produce.

On the upside, more blades equal less vibration. They're used on boats that need more thrust, but they also create more drag.

Bore is the middle of the prop where it fits into the boat's shaft. The bore size has to match the boat shaft size.

Cup refers to a curve at the edge of the blades. Just like your coffee cup, it allows the prop to hold water, or coffee as the case may be.

An un-cupped blade would be perfectly flat (and not very good at holding water). Cupped props can enhance speed and add to the blade's pitch. Pitch is coming up.

You can find the prop's diameter by measuring from the center hub to the tip of one blade, and then multiplying times two.

I won't bring in complicated math here. It's basically the distance around the outer edges of the blades.

More diameter equals more control and power, but it can also increase drag. Large boats require more diameter, and small boats require less diameter.

Drag is pretty much what it sounds like. Something is dragging down, which makes for a slower ride. Drag can be caused by water conditions or, as mentioned above, a prop that has too much diameter for the size of the boat.

Like the pitcher's mound in our proverbial baseball game, the hub, a.k.a. barrel, is the center of the action. It's the middle part of the prop that the blades spin around as well as where the prop attaches to the shaft of the boat engine.

Aluminum: Most stock props are aluminum, which is less expensive than stainless steel but not necessarily as durable. It's fairly easy to repair a slightly-damaged aluminum prop, but if the damage is too dramatic, it can't be repaired.

Composite: Composite props are made out of a plastic polymer substance and are the least expensive to produce. The composite prop's main job is to protect the inner workings of the boat.

They're actually designed to break off if they hit something, in order to avoid damage to other parts of the boat. Price-wise, it's much less painful to replace a prop than your boat's whole lower unit.

As we all know, there's no crying in baseball, but there can and will be crying in boating when you have to shell out thousands of dollars to repair that lower unit.

Stainless Steel: Stainless steel props are very durable, but they're also the most expensive. They're meant to provide high performance as they protect the shaft and gears. After-market props are usually stainless steel.

No, it's not what the guy with the ball does in a baseball game. Well, okay, it is, but not in this particular instance.

Pitch refers to the measurement that the prop goes around in one full rotation, but there's also a hypothetical side to it.

For instance, a 23-inch propeller should move 23 inches in one rotation. Makes sense, right? Now here's where the hypothetical part comes in. That's just the distance it could go if all conditions were perfect.

Let's be honest. Are all conditions ever perfect? Factors like cupping and slip play into this, so it might not actually be 23 inches.

When there's more pitch, the boat goes faster. Likewise, less pitch means less speed. Boat propellers can have controllable pitch or be self-pitching, but we'll get to that in a minute.

Rake refers to the degree of slant on the blades. They slant to either the front or back of the hub.

If the blades are raked, or slanted, toward the front, it can help to increase speed. Think of it as digging with a shovel. It's much easier, and faster, to dig out a spot for your petunias with a curved end than a flat piece of metal, isn't it?

Here's an example of a prop with a high angle of rake.

This is an easy one. Rotation refers to the turning of the blades, either left or right. Rarely are there switch hitters in the propeller world.

Much like the wind, slip is something that's always changing. Slip works in conjunction with pitch, as described above.

It's the difference between the theoretical distance the blade could revolve and how far it actually does revolve after taking into consideration all of the external factors.

Slip can be affected by water conditions, the wind or even the boat's weight and design. As the boat slows down, slip increases. It decreases as the boat goes faster.

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Types of Boat Propellers

Controllable pitch.

Controllable pitch, also called variable pitch, is when the blades rotate around the axis, much like helicopter blades. Boats like ferries and tugboats use this type of prop as it needs a really big hub to turn the blades.

Fixed Pitch

In fixed pitch props, the blades are just that, fixed in place. They don't move around the axis. Most boats use fixed propellers.

Skew refers to the shape of the blade. Skewed propeller blades have a slight angle or curve along the side, like a leaf. Skewed prop blades help to reduce cavitation and noise.

The Best Boat Propeller for a Pontoon Boat

Big rounded blades that give a more responsive, but slower, ride
Four blades can be beneficial because of all the surface area
High diameter
Low rake angle

Our Choice: Solas Amita 4-Blade Aluminum Propeller, 13" diameter x 15" pitch

The Best Boat Propeller for a Deck Boat

The best boat propeller for a ski boat.

Three or four blades
Moderate pitch, but higher than a pontoon boat
Light cupping
Less diameter for less drag through the water, creating the ability to go faster

The Best Boat Propeller for a Speed Boat

Whether you own a Scarab or Stinger, have adrenaline issues or you've watched one too many episodes of Miami Vice (or perhaps all three), if you have a speed boat, you want to get there and get there quickly.

Besides looking sleek and colorful, speed boats were designed for racing and going fast, and it's apparent in their propellers.

High cupping
Specialized stainless steel props with thin blades

Our Choice: Turning Point 3-Blade Stainless Steel Propeller (check price on Amazon)

Hopefully, I've covered all the bases (pun intended) with this propeller tutorial. Now, get in the game and get out on the water!

choosing a selection results in a full page refresh

The GORI folding propeller has amassed a record and reputation unmatched throughout the world of propellers for cruising and racing.

Geared blades.

Geared blade design ensures that the blades open and close together giving less vibration ahead and astern.

Gain a Full Knot of Speed

GORI folding propellers reduce total drag by up to 35%. This results in one full knot of improvement in speed under sail.

Full Power Astern

A GORI propeller gives you the optimum thrust in reverse by virtue of it’s propeller blade shape and profile. It does not rely solely on centrifugal force to open the blades as do many other folding propeller types.

History of GORI

Read a brief history of GORI propeller in Seahorse Magazine.

Reduce Drag up to 35%

Increased efficiency +11%, benefits of gori propellers.

No rotation under sail. No strain or loading to the transmission.
Blades have both camber & curve (aerofoil) to their shape.
Increases efficiency (thrust) under power and over a greater Rpm range.
Lower propeller noise from blade wash due to curve of blade.
Dramatic reduction in prop-walk (almost non-existent).
Overdrive function allows for a pitch increase over normal of approx. 2″-3″.
Simple installation. No gear & blade assembly or pitch settings to make at time of install.

GORI 2-Blade

For shaft and saildrive, with engines up to around 50HP

GORI 3-Blade

For shaft and saildrive, with engines from 10HP to 300+HP

GORI 4-Blade

For shaft and saildrive, with engines over 150HP

For shaft and saildrive, with engines up to 110HP

New from GORI

GORI 3-Blade Single Pitch

No Overdrive For shaft and saildrive, engines from 10HP to 300+HP

Quality Construction

All propellers sold by AB Marine are manufactured from NIBRAL, a metal alloy made of nickel, aluminum and bronze. NIBRAL is far stronger in all specification areas than manganese bronze (commonly used by other prop manufacturers).

Tensile Strength

Impact strength, fatigue strength, 0.2% proof strength, cavitation erosion resistance, corrosion resistance, testimonials.

For the last five years my boat, a Catalina 270, has struggled to get through the water under power, especially against a tide or current. After talking with Geoff at AB-Marine, he suggested a GORI folding propeller. I installed it in the spring and it has made an amazing difference. The speed has increased with less rpm’s, the boat is much more maneuverable and responsive in forward and reverse and I have no trouble making my way through an oncoming current. The new prop has been the best upgrade I have made yet.

– Steve Taylor | Catalina 270

Since it came from the factory six years ago our 46 foot sailboat had a fixed three bladed (speed brake). In a quest for more efficient sailing speeds we recently purchased and installed a GORI 3-blade Folding prop. To our delight our new GORI prop has increased our sailing performance one to two knots and we have also gained over a knot while under power. Soon we will leave San Francisco Bay and begin our cruise to the south and on through the Panama Canal to the Caribbean. With our new GORI prop we will arrive at the fun anchorages even sooner.

– Anna & Steve Sabree | Hunter 46

The Gori 3-Blade propeller has proven invaluable. Our boat’s prop-walk-to-port drove us into neighboring boats until we changed to your 3-blade folding propeller. Now we can easily and safely power in reverse to starboard. Another pleasant surprise was the forward power that a combination of our little 18hp engine and the Gori 3-blade over-drive function provides as they lift our 32ft sailboat’s bow to surge across the bay.

– D. Holden | Beneteau 323

Just want you to know that the 3-blade GORI prop is fantastic! I consistently get at least a 1/2 knot improved performance over my old 2-blade folding prop and the boat doesn’t bog down in head winds & seas. Thanks for steering me to this product, it is worth every cent. Sorry I haven’t had a chance to run flat water RPM sea-trials for you, been too busy racing and doing deliveries to regattas.

– Steven | C&C 115 – Primal Scream

Hi Geoff, I am writing you on route from Newport to Martha’s Vineyard. The GORI 3 blade 15” x 12 x 3 RH propeller has performed beautifully for my Catalina 350 with Universal M35, rated at 35hp, 3000rpm, with the 1.88:1 ratio, RH rotation, 1.00” dia. shaft. I just want to thank you for your assistance, after what we think was a tressle strike a few days prior to the parade when we discovered that the blade had come off our old Autoprop. Thanks again.

– David Olio | Catalina 350

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Model of Interest: 2-Blade 3-Blade 3-Blade Single Pitch 4-Blade Race Series All Models

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PROPELLERS FOR YOUR SAILBOAT

GORI Propeller design and manufacture some of the world’s most efficient and manoeuvrable folding propellers for yachts.

GORI PROPELLERS SINCE 1975

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GORI Propeller supplies a full range of folding propellers and custom-made propellers for leisure projects all over the world. Superior stopping power, second to none due to the unique design of the propeller. Our folding propeller range offers the following products:

2-blade folding propellers.

The 2-blade GORI Folding Propeller is designed for sailing yachts fitted with engines up to approximately 60 HP (44 KW). Tests show it’s highly efficient in comparison to many alternative two and three blade feathering and folding propellers available. Looking for efficiency and less vibrations, then look no further.

2-blade Racing propellers

With GORI Racing Propeller, everything is geared towards speed. From the intricately designed aquadynamic shape and the ingenious folding mechanism to the precision engineering. When looking to reduce drag the Gori Racing Propeller is the choice for the majority of One Design racing yachts. .

3-blade Folding propellers

The 3-blade GORI Folding Propeller is the only folding propeller operating the same pitch in forward and in reverse. This is a technological and functional leap forward in the development of sailboat propellers. Gain the folding propeller’s speed advantages under sail, and the fixed propeller’s thrust capability when motoring.

3-blade Overdrive propellers

The 3-blade GORI Overdrive Folding Propeller give the helm the ability to choose the pitch and profile of the blades without the use of hydraulics or complicated mechanical devices. One propeller. Two settings. When in Overdrive there is less engine noise, less vibration, and better fuel economy. It really is that simple.

4-blade propellers

The 4-blade GORI Propeller has the lowest drag all four blade propellers. It has the same features and operates the same way as the 3-blade GORI Propeller, with the blades pivoting 180 degrees between forward and reverse, providing the same thrust in both directions.

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Low Drag Sailboat Propellers

West by North are specialists in low drag, feathering and folding propellers. We manufacture and supply propellers for any sailing boat, anywhere.

The Campbell Sailer propeller is designed and manufactured to be one of the most efficient fixed blade sailboat propellers on the market today. Unique and innovative, it has been granted a Canadian patent.

After nearly thirty years of production and refinement, the Campbell Sailer has proven, against other leading fixed blade designs, to be a superior choice for sailboat owners.

The Autostream line of shaft and sail drive feathering propellers provides the ultimate in low drag performance under sail, and high performance under power. Manufactured of quality stainless steel, the service life is a high performance story in and of itself.

From Auckland, New Zealand, the KiwiProp is a simple solution to the low resistance feathering yacht propeller.

Features include auto blade alignment with water flow, preventing autorotation for best performance, adjustable pitch and no gears!

The Slipstream folding propeller was designed using many years of collective experience to achieve three main goals: • Outperform competing brands • Provide a long service life, while being user-serviceable • Develop an enhanced product at a competitive price

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Sailboat propeller drag

2008, Ocean Engineering

All but the smallest classes of modern keelboats are fitted with inboard engines and consequently, when making way under sail, the craft experience parasitic drag due to trailing propellers and associated appendages. The variety of screw configurations used on sailing boats includes fixed-blade, feathering, and folding set-ups, with blades numbering two or three. Although the magnitude of the resultant drag is thought to have a significant influence on sailing performance, the published literature having regard to this problem is sparse. Here, the aim was to evaluate the drag effect of fixed-blade propellers of types commonly used on sailing craft. The results of towing tank tests on full-scale propellers are presented for the locked shaft condition; these are presented along with reconfigured data from the few previously published sources. For the case in which the propeller is allowed to rotate, tests were conducted on a typical screw with a range of braking torques being applied. It was hypothesised that the performance coefficients of the Wageningen B-Screw Series could be used to characterise adequately the types of screw of interest and that these could be extrapolated to enable prediction of the drag of a freewheeling propeller; an assessment of this formed part of the investigation.

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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.

Propeller Model	H20	H5	H6 H9 H62	APS H20	APS H5
Propeller Diameter (in)	13" - 17"	15" - 20"	19" - 35"	13" to 17"	13" to 20"
Shaft Diameter (in)	7/8" - 1 1/4"	7/8" - 1 1/2"	1 1/2" to 3"	Saildrive Spline	Saildrive Spline
Engine Power (HP)	up to 40 HP	up to 75 HP	up 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.

Michigan Wheel is the world leader in supplying boat builders, engine manufacturers, and boat owners with high quality, performance propellers. Learn about our Inboard Propellers below.

SAILBOAT SERIES PROPELLERS

SERIES PROPELLERS

Michigan Wheel knows that sailors demand the most out of their vessels. That’s why we offer a wide variety of propeller styles available to get the most out of your sailboat while under power or under sail. Our sailboat propellers may be machined to fit a full range of metric standards as well as SAE standard taper shafts.

Sailer 2-Blade

Our Sailer fixed pitch propellers are very popular among sailboaters. The 2 bladed Sailer fixed pitch propeller is the best choice for sailboaters seeking to maximize sailing speed. It offers minimum drag while under sail and the power to get you where you’re going when the wind stops blowing.

SPECIFICATIONS

Diameter Range

Sailer 3-Blade

The 3 bladed Sailer is the propeller of choice for cruising sailboats. It offers superior dock handling maneuverability and the power to maintain speed in wind and waves when the weather gets nasty with a minimum increase in drag under sail.

“M” Series Sailer 2

The “M Series” Sailer 2 is an alternative to the Michigan Sailer 2-Blade. With slightly more skew and blade area, the Sailer 2 is a good choice for many sailboats in need of an economical and effective propeller.

“M” Series Sailer 3

The “M Series” Sailer 3 is an alternative to the Michigan Sailer 3-Blade. With slightly more skew and blade area, the Sailer 3 is a good choice for many sailboats in need of an economical and effective propeller.

“M” Series MP3

With more blade area than most sailboat propellers and a small amount of skew, the MP3 is great for sailboats with more power than most. The thrust provided not only produces cruising performance when the sails are down, but also offers excellent maneuverability while docking.

Engineering Services
Wake-adapted technology
Troubleshooting

IMAGES

Beneteau drag test
The Parts of a Sailboat Explained in Words and Pictures
Reduce Drag: Make Your Boat Faster and More Efficient
Gori Sailboat Propeller
Seahawk Low Drag Feathering and Folding Stainless Steel Sailboat Propellers
Propeller Efficiency

COMMENTS

Choosing the Proper Sailboat Prop
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. Advertisement. "For the same diameter and number of blades, folding propellers have 85 to 100 percent less drag than a fixed prop, depending ...
Choosing The Right Propeller For Your Sailboat
Choosing The Best Propeller For Your Boat. Fixed propellers are the workhorses of the bunch, but they have been compared to dragging a bucket behind the boat while sailing. Folding and feathering propellers definitely reduce drag, but unless you are planning on doing multi-day passages, you may not notice the extra ½-1kt that you recoup.
Props: Folding Propellers vs Feathering Propellers
A three-blade fixed prop could reduce your boat's speed by as much as 20 percent. For a medium-sized cruising boat, that might be a loss of between 0.6 and 1.2 knots under sail. Put another way, it could add an hour to a 20-mile daysail. ... A final factor to be aware of when choosing a low-drag prop is the proximity of the propeller to the ...
Folding and feathering propeller test
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 ...
Reduce Drag When Sailing With A Folding Or Feathering Propeller
Other brands include Kiwiprop and Variprop. With a feathering prop, the blades are symmetrical and rotate around a central pivot point and offer as much thrust in reverse as they do in forward gear — a boon for getting into a tight slip. When sailing, the blades align themselves with the flow of water, reducing drag. Advertisement.
Lock your prop, or let it spin?
In practice, the amount of spinning drag will be increased from the theoretical level, as some force will be needed to overcome the friction in the gearbox. Even in neutral, a gearbox will have some internal drag, but this has less effect on the boat than locking the prop. Our test leg had a gearbox, so it closely replicates the real situation.
Understanding Your Sailboat Propellers
Props 101. Out of sight and out of mind, sailboat propellers are often an afterthought for cruising sailors. Ironically, because manufacturers have developed a variety of efficient sailboat propellers designed to maximize thrust under power while minimizing drag under sail, selecting the right prop for a sailboat can be even more complex than it is for a power vessel.
Propeller Drag Under Sail Test
Freewheeling Prop Drag = 20-25 pounds: 25 - 12 = 13 pounds of actual propeller drag when freewheeling the propeller under sail. The locked propeller drag is 2.92 times more drag or a 192% increase in drag over a freewheeling propeller when you remove the test jig from the equation!!!! As I said earlier, the test results are not even close.
Folding Propellers vs. Feathering Propellers
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.
Sailboat propeller drag
The parasitic drag imposed on sailing yachts by a range of propeller set-ups has been investigated. New data generated in towing tank tests has been incorporated with previous independently published findings in order to assess a range of typical two- and three-bladed sailboat propeller configurations in the locked shaft condition.
PYI Inc.
Proven Cruising and Racing Propellers Since 1972. Max-Prop has led the low drag propeller market for 40 years and is still the leader today. Since starting production in the 1970's Max-Prop has proven itself on racing and cruising boats around the world. With over 50,000 propellers in the water, the Max-Prop is tested daily in the harshest ...
Sailboat propeller drag
The proposal being investigated in this part of the work is built around the following three forward-performance characteristics of propellers: (i) Advance ratio: (2) J = V A D · n, where VA is the velocity of advance of the propeller, D is the propeller diameter, and n is the rotational speed. (ii) Torque coefficient: (3) K Q = Q ρ D 5 n 2 ...
Sailboat propeller drag
This design is simple, but has drawbacks. The vehicles will experience parasitic drag due to trailing propellers and associated appendages when operating in the glider buoyancy-driven mode ...
How to Choose the Right Sailboat Propeller
Pitch. The distance the propeller would move forward during a single rotation. Think of a nut and bolt. The pitch of the bolt's thread is equivalent to that of the propeller. When you rotate the nut through a single rotation, it moves forward a set distance. The distance moved is the pitch, measured in inches.
Thinking of Changing Your Sailboat Propeller?
Folding Sailboat Propeller. A 2 bladed folding prop is shown here on a saildrive unit, but 3 bladed versions are also available. On both types, the blades are pivoted and fold backwards under the force of the water flow when not being driven by the engine. It's often necessary to put the engine in gear to stop the shaft from turning which will ...
The Campbell Sailer Propeller
High Thrust - Low Drag. Independent tests by Practical Sailor Magazine show the Campbell Sailer achieves top marks in the fixed blade category for forward and reverse thrust, and for providing substantially reduced drag under sail.. All Campbell Sailer propellers are available in 2 and 3 blade configurations in sizes from 10" to 27" and larger.
How to Choose a Boat Propeller That Won't Drag You Down
Three Blades: Three-bladed propellers are the most common type. They're usually made out of aluminum and are less expensive to produce. Being that fewer blades means less drag, this allows for faster speeds. However, this can also cause more vibration. Four Blades: Four-bladed props are also fairly common.
AB Marine
GORI folding propellers reduce total drag by up to 35%. This results in one full knot of improvement in speed under sail. ... The Gori 3-Blade propeller has proven invaluable. Our boat's prop-walk-to-port drove us into neighboring boats until we changed to your 3-blade folding propeller. Now we can easily and safely power in reverse to ...
Folding Propellers
This is a technological and functional leap forward in the development of sailboat propellers. Gain the folding propeller's speed advantages under sail, and the fixed propeller's thrust capability when motoring. ... The 4-blade GORI Propeller has the lowest drag all four blade propellers. It has the same features and operates the same way ...
Low Drag Sailboat Propellers
West by North are specialists in low drag, feathering and folding propellers. We manufacture and supply propellers for any sailing boat, anywhere. The Campbell Sailer propeller is designed and manufactured to be one of the most efficient fixed blade sailboat propellers on the market today. Unique and innovative, it has been granted a Canadian ...
(PDF) Sailboat propeller drag
Tullio Opatti. 2008, Ocean Engineering. All but the smallest classes of modern keelboats are fitted with inboard engines and consequently, when making way under sail, the craft experience parasitic drag due to trailing propellers and associated appendages. The variety of screw configurations used on sailing boats includes fixed-blade ...
Autoprop Self-Feathering Sailboat Propellers
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 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 ...
Sailboat Series
Our Sailer fixed pitch propellers are very popular among sailboaters. The 2 bladed Sailer fixed pitch propeller is the best choice for sailboaters seeking to maximize sailing speed. It offers minimum drag while under sail and the power to get you where you're going when the wind stops blowing. More info.

Reduce Drag When Sailing With A Folding Or Feathering Propeller

Learn how this time-tested piece of running gear can give your boat a power boost under sail.

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The Importance of Choosing the Right Propeller for Your Sailboat

Folding Propellers

Benefits of Using Folding Propellers

Reducing Drag

Offering Safety

Greater Maneuverability at the Dock

More Comfort

Great Value for Money

Cons of Folding Props

Are Folding Propellers Ideal For Your Boat?

Feathering Propellers

Benefits of Feathering Propellers

Offers Superb Maneuverability

Offers Amazing Reverse

Adjustable Pitch

Cons of Feathering Propellers

Are Feathering Propellers Ideal for Your Boat?

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