The Offshore Voyaging Reference Site

Feathering Propeller Review

When we took delivery of our new OVNI 435 in 2008, we decided to stick with the standard 3 bladed propeller, partly for reasons of cost (we were running out of cash!).

But on all of my previous boats I’d had either a folding or feathering prop, and fully intended to fit one to Pèlerin when money allowed – none of these units are cheap, but the fixed blade could then act as a spare. Fixed props are fine and have predictable characteristics, but as has been demonstrated in numerous prop tests, a fixed three bladed prop has about the same drag coefficient as a boat’s hull.

When under sail, if the gearbox manufacturer allows, the prop can freewheel, that’s about the equivalent of towing one bucket, but if the prop has to be locked in gear, then make that towing two buckets. That will make a major dent in any boat’s performance, especially in light airs. But the prop drag can be reduced entirely by fitting a folding prop, and by over 90% by fitting a feathering prop, so we knew we wanted to make the change as soon as we could.

What Prop to Choose?

A folding prop was not possible due to space restrictions and memories of poor astern propulsion leading to heart-stopping moments in tight corners. The small aperture around the prop also meant that the interesting Autoprop, which has performed well in a number of trials, couldn’t be fitted. As ready cash was still in short supply, the excellent Variprop we’d had on our previous boat for many years was out, as was the highly recommended Maxprop, too. An interesting development at a good price looked to be the Kiwiprop, with its Zytel blades, so we decided to give it a try.

We were happy enough with the swap, and could soon see the benefits in terms of our daily average runs. Performance under power was good, although the grip astern was less impressive. It was pretty noisy, too, although that wasn’t helped in our boat by natural resonance coming through the flat aluminium plate above the prop. Overall, we were happy enough with it at the price.

Sadly, the prop came to a sticky end up the Owenboy river in Cork, southwest Ireland, when one of the rollers (that stop the blades from traveling too far in astern pitch) came out. A diver carrying out a brief inspection also removed the other two rollers, where both pins were bent. There was nothing for it but to remove the prop, send it off for repair, then re-fit the original fixed-blade prop.

The helpful people at Kiwiprop repaired it and sent it back. Their report suggested that we’d picked up a rope or wire that had caused the damage, and the prop had also been upgraded with the latest titanium pins for the blades. But we never got around to re-fitting it, and when we met someone who was looking for a Kiwiprop of the same dimensions, we decided to let it go.

Try, Try Again

We then put that money towards a new prop, and having sought recommendations decided to go for a new British made Featherstream, a three bladed feathering propeller. The Featherstream uses a bronze hub with stainless steel blades –  stainless allowing thinner, more efficient blades that are more durable and corrosion resistant. The prop seems well engineered, came with an exemplary installation manual, and the price was very competitive.

The blades swivel through 180° to present the same leading edge ahead and astern, the pitch can be adjusted externally (although it’s not easy), and maintenance is claimed to be simply external cleaning and internal greasing annually.

We haven’t got much experience with it yet, but the pitch ahead seems spot-on straight out of the box, and astern is particularly impressive with much improved stopping power. Noise levels are slightly higher than with the fixed prop, but by getting the revs just right it’s possible to reduce the resonance significantly. And now that we know the boat well, we can really feel the difference in sailing performance, particularly in light conditions, which is where we’ve worked hard to make an improvement to our boat.

The Good and the Bad News

Are there drawbacks to installing a feathering prop, cost apart? Well, with most flat blade models, cavitation can occur in certain circumstances. I’ve only ever had this happen once, on our old boat whilst punching out of a harbour into a strong headwind with a really nasty short, steep chop, where fortunately we had enough room to ‘tack’ under power. Fine tuning the pitch to suit the boat can help here, made easier if you can adjust the pitch in situ. And as the prop doesn’t turn when under sail the possibility of running a prop shaft alternator is removed. And there’s no getting away from the fact that they are far more complex than a fixed prop, which will not go down well with adherents to the ‘KISS’ principle. But reliability (in my experience) is good, and if properly maintained they give little trouble.

The big bonus is undoubtedly the improvement in sailing performance. All things being equal, we think feathering props make a significant improvement to a boat’s sailing ability at a cost worth saving up for. Better light airs performance should translate into less fuel consumption and so greater range and endurance – all worthwhile benefits for cruising to remote areas.

Have you had any experience, good or bad, with these or other feathering propellers? Please leave a comment.

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Oh no! The dreaded rotating vs. locked prop issue has been raised.
Actually, a locked prop has much less drag than a rotating prop.

A Kiwiprop fits in well with the KISS principle.
Hold on to something before engaging reverse.

John Harries

Hi Rikki

That’s an interesting one, but I’m not sure the answer is that clear. At one point I was on your side and my justification was that a helicopter that has an engine failure and a jammed rotor falls like a rock, but one that has the same failure but can allow the rotor to spin can land, albeit it hard.

On the other hand, when I was a PHRF handicapper years ago, we did some tests and the answer seemed that in most cases the boat was faster with the prop rotating.

I suspect that the answer may lie in the pitch and blade shape of the prop in question. If the locked prop is fully stalled, then lift and therefore drag would be lower. But if flow attaches to the locked blades, then perhaps drag is higher, since, as I understand it, lift and drag are directly linked—more lift, more drag.

Bottom line, I’m just confused!


When I was still flying, we always feathered the prop on a dead engine. If we couldn’t feather it but could lock it we would. Our range and glide ratio improved. Our understanding was the drag associated with the tip vortices of three stationary tips was less than the very large spiral vortex of vortices associated with a spinning prop.

Colin Speedie

Hi Rikki and John

I’d always believed that a locked prop (with a fixed prop) caused more drag – certainly looking at the turbulence behind our Ovni when under sail with the prop locked (experimentally) in reverse with the three blader it seemed far worse than when the prop was allowed to rotate. But as you suggest, there are reports to the contrary, and I’d love to hear the definitive answer.

Not that we had a choice as our gearbox manufacturer (Hurth) state that the prop should be allowed to rotate with a fixed prop, and only locked in reverse with a folding or feathering prop.


Our experience is it is better not to put the transmission in reverse even with a feathering prop. When a prop sits in a free flow stream (such as a test tank) it sits there quietly, unmoving. When it is in a natural environment with the swash and eddies that spin off the waves, hull, canoe-body, skeg, strut, etc, they don’t rotate, but they do move. In our first year with our prop (and a Hurth)—after a long sailing leg locked in reverse, we found ourselves completely, irrevocably locked in reverse. We had to start the engine that way. Since then we let the transmission stay in neutral when sailing feathered. Mfg rep said we were not the first to observe this…


Here’s the skinny from one of my aero-hydrodynamics friends. IT DEPENDS.

Imagine the following:
Water is flowing down a stream and across a straight rock lip. It cascades off and flows into a new stream. From time to time if the lip flow is disturbed, a small bit of super critical flow will cause a stronger dribble, but it won’t last long and the flow will straighten back out. This is form drag caused by the water turning a sharp corner. This is water flowing across the edge of a locked prop. Partially contrary to my earlier remark, vortex formulation is rare with a sailboat locked prop in a free flow environment. (More on that later).

Now think of the pictures you’ve seen of spinning, vortex forming propellers in operation. In the design process, vortex formulation is minimized by shaping the propeller twist and tip curve — for normal cruising prop RPM.

Now consider a free-wheeling prop now spinning in a condition that puts it well below design cruising rpm but well beyond the water flowing over a rock lip mode. In this condition, the prop is at the wrong angle of attack for the water speed compared to its rotation speed so it creates both form and lift drag. Also, the prop twist and tip shape is no longer optimum because the RPM is much lower. Props in this condition become vortex factories [and if you don’t think those create drag, consider all the airliner mods to improve fuel economy by adding tip winglets to shrink the vortexes.] So we now have form, lift and vortex drag all adding up, when form drag was all we had before. But again we are talking about free flow environment.

Non-free flow environments — those modified by hull shape — don’t change the basic physics, but they can change what excites prop behavior. In the end, the biggest factor appears to be vortex formation as a function of propeller rotation speed — which may not smoothly correlate with boat speed due to hull flow effects.

Beyond IT DEPENDS, the general rule we agreed upon was props on struts well away from the hull would be most likely to be draggier when freewheeling than locked. Props in apertures might see no measurable difference. Props under hulls with flat runs aft might also see more rotational drag than hulls with greater deadrise aft. Also if one’s keel sheds significant turbulence at prop level one may see a sinusoidal pattern imposed on the prop rotation speed as fluidic effects arise.

In the end, we concluded sailing in both locked and freewheeling conditions on a day with steady winds, under a lee for an equal distance with a stop-watch would provide the best boat by boat answer — for those conditions

John Harries

Hi Chris,

Thanks for the great comment that explains a complex subject clearly. I think I even understood it…on the third reading.


Hi John
The maneuver that helicopter pilots fly in case of an emergency is not about drag but about storing rotational energy in the rotor. See here for an explanation:


I always thought so, but no longer. See

John Harries

Hi Greg,
Thanks for the link. Well that settles that, what a relief!


We were fortunate to be able to fit a Max Prop from day one. We found their guidance on preventing rotation when stopping to be more hull-shape dependent than they realized. Experimentation found the answer. Keeping it full of grease and zinc protected has been key to our ability to trust it.

Colin Speedie

Hi Chris

I’m intrigued by your findings re hull shape – I’ve noticed that with all of the feathering props I’ve tried the prop would occasionally rotate slowly, but have always just put the gearbox astern and that’s been it.

Maxprops have a great name for reliability, and although I’ve never had one, our last boat had a German Variprop for seven years of hard work, and was faultless. And we never did more than you mention – just grease and replace the anode once a season.


When shutting down, we:
drop to idle,
shift to reverse,
accelerate to 1200 rpm for a three count,
shift back to idle and shutdown simultaneously.
The prop “flops” from reverse to feathered and stays there.

Colin Speedie

Hi Chris

Thanks for those three thoroughly enlightening comments – real food for thought.

Following your first comment that segues nicely into the third, I’ll change my ways – and there was I thinking it was all so easy. Our boat has a very flat run aft, which may explain why we saw so much turbulence from the old prop when locked.

And thanks to you and your aero/hydrodynamic friend for such a lucid explanation of a previously opaque subject!

Best wishes


Geir ove

We had a 3 blade Gori on our mono, no problem. Very happy with it. Change out the zinc and rubber dampers every 2 years. On our new Cat we will have 2 Maxprops, and hope to be happy with those? Saildrive this time.

Denis Bone

I installed an Autoprop a few years ago. I had to cut a chunk out of the rudder leading edge to allow enough space for the prop blades to swivel but my Fisher Freeward 30 has a huge rudder and this made no difference to steering. Performance is everything claimed for the propeller both ahead and astern but most impressive was the more than one knot increase in sailing performance. Only complaint, the plastic screws holding the anode are impossible to really tighten because they feel as though they are about to break before they are satisfactorily tight. I also got the impression that the tapped screw holes in the boss were fouled and the plastic screws were not capable of clearing the fouling. The holes must then be cleaned using a plug tap and probably removing metal every time you change the anode. Brunton provided me with stainless steel screws and advised me to coat the areas of the anode around the screw bosses with antifouling to prevent them corroding away, as was happening, resulting in the anode falling off.

Colin Speedie

Hi Denis

We would have liked to try the Autoprop, but lack of space due to its shape ruled that out. On the face of it, they seem to offer so many benefits, and your experience certainly seems to bear that out.

The antifouling tip re the stainless screws is the same one that we use – and saves a lot of time, money and hassle in terms of early replacement of the anodes.


Ever had any kelp or similar around the Autoprop?

How does it cope? It kills a normal prop, but at least you have enough grunt left to (hopefully) get you out of trouble…


I am thinking that getting a feathering or folding prop might improve my performance to windward and in light airs by much more than any other way I could spend that money (except by spending it on Diesel…).

Also did it improve the handling under sail, with less turbulence over the rudder?

Anybody heard anything about the 2 bladed CDI feathering propeller, looks like it’s almost within my budget.

I must say I have been impressed with the way a Slipstream with SS blades ate up any chunks of ice that went through it…a crunching sound like an ice machine and that was it, and lots of little ice cubes astern…I’m not sure if a Kiwiprop or CDI with plastic blades would fare so well?

Colin Speedie

Hi Ben

I’d agree that fitting a feathering prop will do just what you suggest – the performance benefits are noticeable throughout the range, so they represent money well spent to me.

Re the turbulence over the rudder and improved handling, certainly the boat feels a little nicer to steer in light airs, but I might be confusing the more sprightly performance with crisper steering – and as we have over tight new rudder bearings it’ll be a few miles before we can say for certain!

Stainless blades should be tough, and it’s good to hear that they cope well with ice, but equally the Zytel blades on the Kiwi should be equally tough. Zytel (I’m told) is extensively used in race cars so must be pretty durable, and it certainly wasn’t a worry for us, although we weren’t in the ice…


I suppose in the interests of safety I should add that any ice we hit with the prop was pretty small. If we were in heavy ice the engine revs and speed were kept near minimum to stop ice going under the boat. If we hit a bigger piece unexpectedly and it went under the boat (Thud bang bang wince…) we would leap for the throttle and put her into neutral as quickly as we could to try to protect prop, and drive train…

Peter Holzinger

Colin, How did the price compare between the Kiwiprop and the Featherstream? I was planning on fitting a Kiwiprop to my Tartan 37 this summer and have not considered the Featherstream as of yet. The Kiwi is $1500 shipped. Do you agree with the general principle that the Kiwi should increase my boat speed under power by about a full knot? I run a Westerbeke 50. Thanks for the great article.

Colin Speedie

Hi Peter

I’d reckon about $1000 more, but it would be best to get a quote. We ordered ours during the Southampton Boat Show on a special offer and we got a very good deal.

As far as speed under power, I’m not so sure. I can’t say we noticed it with the Kiwi, but it might be very dependent on sea state, for example. With the Featherstream in flat water we are running around 200 rpm less at 6 knots than with the old fixed prop, but I’d prefer to reserve judgement until we’ve tried it in a range of conditions.

Alan Teale

We considered the Autoprop, but when questioned Bruntons informed me that with our appropriately sized hydraulic gearbox an Autoprop would rotate when not under power. Bruntons answer was to accept it, or fit a shaft brake, or fit an oversized box with enough inherent inertia to overcome the prop’s tendency to spin. We went for Maxprop.

Paul Mills

Hi Colin

We fitted a Featherstream from new – keeping the fixed standard prop in the bilge as you have wisely done…

After one season’s use I have to say I am very happy with it – and agree with the stopping power! Thus far we are on our second anode and have applied paint around the bolts on a tip from Stephen J. I have found the cavitation an occasional problem, the best being crossing the bar at Morston on the Norfolk coast – short steep seas…but get round it by reducing revs a bit and then increasing once the water speed goes back up.

I too was very happy with the price and serviced it in half an hour last week.

Colin Speedie

Hi Paul

Good to hear another positive review especially when it agrees with mine!

We haven’t found any cavitation yet with ours, but I’m hoping it’s like our old Variprop where we only once saw it – it seems to just be in a particular set of circumstances, and I’ve not heard of any propr that seems to suffer from it more or less than another, unless, perhaps, the pitch isn’t spot on.

Donal Philby

Our current boat has a Sabb variable pitch prop—no transmission—just continuous adjustment from full forward to full reverse. I can’t imagine going back to any other kind of prop. Docking is done at a constant RPM and speed (down to barely moving) controlled by the pitch. While sailing we hide the two blades at full pitch vertical in the aperture. I spoke to a sailor who moved to a Maxprop and found that his slowest speed was 4 knots. Hundested makes VP props for engines of 150hp & up. Several years ago Sabb stopped production on their diesel engines, but adapted their VP system to other more modern engines (they produce life boat engines), and appear to have a standalone VP prop and gear box worth investigating.

Sergio Del Castillo

Hi Colin,
Thank you very much for such interesting conversation. Great to read you all.
I would like to talk about some unexpected consequences of these kind of propellers.
I have a MaxProp on my boat, a Jeanneau Sun Odyssey 45.2 equipped with a Yanmar 75 HP. Regarding performance and maneuverability, the MaxProp gets without doubt the best qualification.
But during these years I have had some problems with my silentblocks. Every 500 h approximately I found one or two broken (not the rubber, the bolt used to give the right height to the engine). Each time, I change them, checking shaft alignment and engine position. Always under the supervision of the Yanmar dealer, and trying to do those jobs with great accuracy. And again, after the next 500 h, the problem returns. We then checked all what we did again, finding that everything was perfect. Then we checked for electrolysis or static currents, and found nothing.
Next time with broken silentblocks I changed the shaft, to be sure it was completely straight, and added a deflector in line, to avoid vibrations to the engine through the shaft. This last action was suggested from Yanmar, because they believe that feathering propellers, when changing under normal conditions from forward to reverse and vice versa make a knock that damages the silentblocks. I was told that in some cases, if the engine is equipped with feathering props, like MaxProp or Gori, guaranty has no effect at all.
Now the problem seem to be solved, but I would like to know if any of you has suffered similar problems, and if the case, what are the conclusions.
Thank you for this opportunity, and excuse me for my English, sometimes it is difficult to express complicated ideas.

John Harries

Hi Sergio,

This is interesting. I know another boat with the same engine and a Maxprop that has had to replace the Yanmar mounts too.

Since you have checked everything so carefully, I suspect that these mounts are just not strong enough to take the shock loads imposed by a feathering prop. And they should be. Saying that a feathering prop voids the warranty is just not good enough since many, perhaps most, sailboats have them. Either Yanmar want to sell to the sailboat market, or they don’t.

If memory serves, that engine is based on the old 40 to 50 HP naturally aspirated Yanmar block. My guess is that when Yanmar juiced it up to 75 hp they neglected to up-strengthen the mounts to take the increased power.

Of course Yanmar will probably, like most manufacturers with a problem, claim that you are the first to have this issue.

Perhaps you might consider replacing the Yanmar mounts with a stronger after-market mount. You might need to have custom mount brackets fabricated, but it sounds like it might be worth it.

Also, one other thought. Is it possible that the idle RPM on the engine is set too high? This would result in a larger shock load each time you go from forward to reverse and vice versa.

And finally, please do not apologize for your English. If only I wrote any other second language, half as well as you write English, I would be very happy!

Sergio Del Castillo

Hi John,

Thank you for your kind answer.
You are right about the Yanmar mounts. I asked the technician about this. He made the question in Yanmar and got the answer that this engine has the right silent blocks, and all of them in the same size. However, older engines had bigger mounts and also there were differences between fore and aft units.
So probably you are right about your guess. Maybe this is also a way to reduce price in the final product.
Taking in consideration Yanmar’s answer, I took off my head that the problem could be in the mounts themselves. I think I’ll consider this again if the problem comes again.

The idle RPM is set at 700, so I think that this can’t cause the problem, but it’s true that it’s important.

And finally, congratulations for the site, simply great.


Jim Patek (S/V Let's Go!)


Probably a bit late to comment given all the other good input. But…
We had the Maxprop installed when our Ovni was launched in 2003. It took me about six years to figure out that after getting the prop to feather by putting the transmission in reverse, that I could then put it back in neutral and all would be well. This was a good thing because I cannot tell you how many times I started the engine, full tilt, in reverse (this after warning the crew to always put the transmission back into neutral before starting the engine).

The other great thing about the Maxprop, and probably the others, is that you can adjust the pitch so that you can move along at 4-5 knots at low RPM using not much fuel to make incredible distances when the weather is calm. I know this is heresy but with nearly 5000 hours on the Volvo, so far so good. Of course, it is a matter of degrees, literally. When in Ecuador, the Maxprop had to be removed to pull the shaft to replace the weak cutlass bearing (that I have commented on once before). When it was replaced, the boys set the pitch much higher than the recommended setting. However, it was not until Tonga, when I tried to make it to an anchorage before dark, that I found out I could not go faster than 6.5 knots. I now have the pitch set two settings below the recommended setting and could easily do a third without sacrificing top end speed. I miss that Ecuador pitch, whatever it was.


Colin Speedie

Hi Jim

Fascinating comment, and one I’ve never heard mentioned before. I wonder what the effect on fuel consumption is? Especially as the Ovni’s aren’t gifted with huge tanks.

Noted your point, too, about pulling the shaft to replace the cutlass bearing – we’ve just done the same, and it was only just achievable. I certainly wouldn’t want to try it between tides on a beach, except in a dire emergency.

Jim Patek (S/V Let's Go!)

Hi Colin

I checked my records from back in the day and I used about 1.5 l/hr on average. I recall that I motorsailed at 1100 RPM, motored at 1400-1500 RPM and charged at about 1800 RPM in neutral. This was before installing the wind generator and Mastervolt 3.8 kw generator. When I had the boat built I had Alubat install a third 100 litre tank and I carry 5 22 litre gerry cans in the stb aft locker. So, before I learned that the pitch was a little OTT, I could motor sail a long, long way.

The engineer at Gulf Harbour Marina in New Zealand reset the pitch to the recommended setting. He said that as long as the engine could reach 2800 RPM while the boat was tied up at the dock, that the pitch would not be too great. At a later haulout we increased the pitch one setting (I am pretty sure about this but don’t have my info with me-it could have been two) and still had no trouble reaching max revs and that is where it sits today. I now use 2.5 liters per hour at 1600 RPM and 3 liters per hour at 1800 RPM.

Hope this helps.

Colin Speedie

Hi Jim

That’s all good food for thought. I wish we had had the foresight to add an additional tank, but I also think that we were on the limit of what Alubat would allow in terms of additions – we had asked for a lot of changes.

Once we get back to our boat, and have the chance to check our ‘new’ fuel consumption levels, we’ll have a look at whether we should adjust the pitch on the Featherstream.

Best wishes


John Harries

Hi Colin and Jim,

When we re-powered we spent a lot of time on the prop pitch issue and had several very interesting conversations with Steve Dashew on the subject.

I have started working on a post on the issue. In the mean time, part of what I learned is here.

Jim Patek (S/V Let's Go!)

Hi John

Got the spreadsheet with the tip speed formula. I will try the calculation out when I get back to the boat. Thank you.

Geoff Skinner

This is a very good discussion. I would like to know if anyone has information on Maxprop or any similar prop acting up in a heavy following sea? I had such a situation recently on a passage south along the Portuguese coast from Lisbon. Loud clunking sounds coming from around the region of the P-bracket. I thought we had picked up a pot but no. The Maxprop was locked in reverse (I thought), but on every second or third wave from astern there was a loud “clunk”. All I could think of was the prop flipping orientation in the seas. We were wing ‘n wing in 25knts almost dead astern. Next morning the sea state had calmed a bit, the wind angle changed to a broad reach and the noise was heard no longer. Any thoughts every welcome. Thanks Geoff

John Harries

Hi Geoff,

Well that is indeed strange. I have been using Maxprops for over 35 years and well over a hundred thousand miles and have never had that problem. I wonder if some piece of debris was lodged in the blades, so they were not fully feathered, that came clear later on before you had a chance to inspect it.

Alan Teale

Dear All, I mentioned above that we went for the Max Prop rather than the Autoprop because Bruntons predicted the latter would spin our hydraulic gearbox rather than feather. Has anyone with an hydraulic box had problems getting the Max Prop to feather using the recommended procedure?
Thanks to Colin and everyone for a really useful discussion.

John Harries

Hi Alan,

We have been using Maxprops for nearly 20 years, first on a Borg Warner Velvet Drive and now on a ZF. Both are hydraulically activated transmissions and therefore do not lock.

We simply stop the engine with the transmission in idle ahead, as instructed by Maxprop, and the remaining hydraulic pressure in the transmission locks the shaft for long enough that the prop feathers.

Very occasionally, perhaps once every few years, the prop fails to feather. But just re-starting the engine, cycling between forward and reverse a couple of times, and the shutting down in forward has always solved the problem.

I suspect that the problem in these rare cases was that there was a bit of weed or something on the prop.


Sergio, Hola
As you said, engine bolt fractures are more likely to come from vibration, not the “gentle” tap a feathering prop makes when it seats in forward and reverse. Vibration heats the bolt metal, which causes it to lose strength and break. The relatively tiny shock of a feathering prop seating just won’t make that happen.

A feathering prop can increase vibration if there is too much unsupported shaft between it and the shaft log where the shaft exits the hull or the last strut — but this is only true when the feathering prop is much heavier than the prop the boat was originally designed for. [We shortened our shaft to minimize this distance.]

It would be very interesting to see the engine mount bolt ISO strength marks on the heads of the broken bolts. It is not uncommon for boat yards and boat builders to use the correct length and diameter bolt without verifying it is the correct strength.

Also, has it always been the same bolt location? The length of bolt between the upper and lower nuts can cause each bolt to vibrate differently.

Also, does the engine have any non-standard items such as a second or larger alternator mounted? These can change the vibration modes of a mounted engine significantly. While their vibration will be similar to the main engine vibration, it can be just different enough it can cause a “pulsing” that could affect an under-strength bolt.

None of this may help, but I just don’t see the prop seating in forward and reverse (which happens fairly infrequently per engine hour) being culpado.


Sergio Del Castillo

Hi Chris,

I’ve been discussing a lot about this with the Yanmar technician. I told him the same arguments you are using: compared with possible vibrations, the smaller number of times that the prop seats from forward to reverse could not cause the problems. But he was firm in his position, so I tended to give him the reason.
Maybe the weight of the MaxProp is bigger than the original one, and this could explain some of the issues. I’ll check this point. Anyway, as John pointed out, there are lots of Yanmar engines with this kind of props…
After a long time, when I installed a deflector between the engine and the shaft, the whole longitude increase about 5-6 cm, so now the prop is fairer, and of course that could be a new source of vibrations… It’s a never ending story, like with secondary effects in medicine…
Yours is a smart point to have in mind.
The broken bolt was different every time, but most of the time I had more than one broken when I heard the clack-clack that announced the show. I’m not sure what bolt was the first to act and maybe break the others.
The only non standard item on the engine is a high charging load alternator, replacing the old one, but more or less is the same size and weight.
Now I have the boat on the yard, so I’ll be able to “play” again with all this information.
And thank you very much for your time!!!



De nada. It will be interesting to hear what you discover. C


John, one of the most gratifying things about this site is a civil discourse.

Colin Speedie

Hi John

I’d like to second that – really great comments on this subject from which we can all benefit. There’s a real wealth of experience and technical and theoretical knowledge on display here – keep it coming, folks, and thanks to you all so far.

Best wishes


Denis Bone

This was a response to Ben’s question of 03/04/11, I mistakenly sent it to e-mail rather than the website! Sorry for the delay Ben!

I am not aware of ever having had weed or rope around the Autoprop, I did install a ropecutter and it may have worked perfectly!

My boat originally had a Sabb variable pitch propeller similar to Donal’s. Like him, I found it very easy to control using the pitch only but I also found it very vulnerable to mono-filament becoming jammed between the blade flanges and the boss. This froze the pitch controls and the only way to remove it was to strip the propeller. If this was attempted underwater, using scuba gear, I found it advisable to hang an umbrella from the prop shaft to catch the bits you would inevitably drop!

I suspect the Autoprop may be similarly susceptible although it has not happened so far and, assuming only one blade was jammed, you would retain drive and control on the other two.


Without a doubt, the umbrella suggestion is one of the best “tweaks” I have heard in a long time! Good on ya!

Pete Worrell

We have had an Autoprop on our vessel for over ten years and never had any problems with it. When we compared it to the Maxprop that we previously fitted, we found that our speed increased on average, and our fuel efficiency increased on average. The most important advantage of the Autoprop (that hasn’t been mentioned) is that when you are motor sailing and get a puff, the blades immediately open up the pitch, so at the same engine rpm your speed through the water increases noticeably, allowing you to make passages much faster and more efficiently at a given engine RPM.

Pete & Kareen Worrell


Thanks for the reply, I do like the umbrella tip. So they do have a use on a boat then…and they are not one of the three useless things on boat as claimed…

I guess the reason I asked is that twice I have got caught in heavy kelp, and nearly stalled the engine once (70 hp forward) and lost most of the thrust with another (4bt Cummins). In both cases we still had just enough drive to extricate ourselves…Once clear of the kelp a few bursts ahead and astern cleared the prop and we were fine.

Neither boat had rope cutters which might well have helped. One was a fixed 3 blader the other was a standard feathering prop. So although wrapped in a ball of kelp the pitch was still normal.

The sensitive balance between rotation and lift that sets the pitch of the Autoprop’s blades would seem like it could be badly affected by the drag of kelp or seaweed on a blade. As a prop they sound brilliant, but is this a weakness? It would be interesting to find out (for once google doesn’t seem to be able to help?).

Tony Price

Interesting reading. In our previous boat (34 ft Farr cruiser racer) we had a folding prop which was fine for that size and weight of boat. We bought our present boat in 1995 (46 ft offshore cruiser centre cockpit), which we have done several trips to the Pacific Islands and long distance NZ coastal cruising. We used a shaft brake for many years to stop our three bladed prop from rotating to at least reduce the drag but when the shaft brake suffered serious damage for the second time we decided to change to a feathering prop.
In 2006 we installed an Italian J-Prop for which our prop guy was the NZ agent. It is a dream to have, much improved light weather speeds, easy to adjust the pitch in or out of the water, only one anode to replace (one bolt) and greasing is very simple and we have done it in the water when on extended cruises with no decent haul out facilities. The J-Prop was significantly lower priced than the MaxProp.

Happy sailing

Nick Mason-Jones

We have just bought a 2004 Moody 47 that sounds pretty similar to your boat, ie centre cockpit heavyish displacement blue water cruiser. She has the original fixed 3 bladed prop fitted. We are hopefully crossing the Atlantic next year and I want to replace the prop with something with less drag that will still give decent performance under power. Are you still a fan of the J prop? Any words of wisdom would be appreciated


John Harries

Hi Nick,

I’m sorry, I’m not familiar with the J prop. We have used Maxprops for 30 years and are very happy with them.

Tony Price

Yes, our boats would be fairly similar. We have had our J-Prop for four years now and have undertaken long distance coastal cruising around northern south island and all eastern coast of the north island of New Zealand encountering very strong tidal flows in channels and a variety of conditions. We also had six months to Fiji return and we were very happy with the prop. It gives excellent thrust and top speed when needed. It has less stern walk than our old three blade fixed prop and has more stopping power in reverse. There has been no sign of corrosion and have only recently replaced the prop and shaft anodes. It took us two attempts to get the pitch correct when we installed it. We set the pitch so that we just attained maximum revs on the motor. We found that the prop is sometimes reluctant to feather if it has not done so for a while and now select slow reverse and forward several times before leaving anchor or berth and sometimes immediately prior to shutting down the motor when under sail. The unit is easy to lubricate (one grease entry point which is sealed with a stainless steel grub screw). We did it in the water in Fiji once and it went well. All best wishes for your Atlantic crossing. You can see our cruising blog at

Go well


Hi all, for anyone who has considered but ruled out a Featherstream thinking that it cannot be left unfeathered under sail if wanted, therefore preventing one from using a prop shaft alternator, just want to pass on a reply from the manufacturer to JFE at Boreal:
“The Featherstream propeller in normal use will feather under sail and the shaft will not rotate while sailing. However, if you want to run a shaft alternator while sailing you can. In this case the engine is briefly run in reverse before stopping it. The propeller cannot feather from the reverse position so it will drive the shaft and alternator while sailing. When driving the shaft alternator is no longer wanted, the engine is briefly run in forward then stopped and the propeller will feather as normal and the shaft won’t turn while sailing. Hope this helps but if you need anything else, just let me know.”
So, don’t know what kind of (in)efficiency is achieved with the blades presenting their reverse angle while sailing forward, but at least some rotation seems to be possible…hopefully enough to achieve charging rates not too far below that using a regular prop, guess I’ll find out… —M

John Harries

Hi Matt,

Thanks for the information, very useful.

Kjell Olav

Hi! I own a Ovni 435/2006 with VP 55 engine. Consider installing Feathering propeller. Reading your article from 2011 about Feathering Propeller. Considering Autoprop and Variprop. Do you know the diameter of the propeller. Should it be 19 inches? Do you have recent experience with these two propellers?

Marc Dacey


I have installed a Variprop D-107 four-bladed feathering prop on my 16 tonne steel pilothouse cutter. It is 19 x 15 (nominal pitch, which we haven’t changed to date) and is turned by a Beta 60 engine with a ZF-25 A hydraulic transmission to an AquaDrive CV thrust bearing on a 1.25 inch shaft. In both straight-line motoring and in heavy shifting to maintain position in strong winds, we have been favourably impressed with the torque of this particular model and its responsiveness in allow us to move our somewhat ungainly boat in close quarters. The sizing of your prop will depend on several factors, including tip clearance from the hull, your transmission ratio and your power curve. All I can say is that the positive attributes of a well-built feathering prop for us have been proven in practice. I can also say, having owned a different boat with a folding Gori prop, that the four-bladed feathering Variprop seems much faster in response to shifting and throttle commands.