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Old 25-01-2011, 16:16   #1
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Folding / Feathering Prop on a Pearson 365

I need to replace the prop on my 1979 Pearson 365. As long as I am at it, I thought I might cnside a folding or feathering prop. However, such props are expensive and I am unsure how much I will gain on a boat like a Pearson 365. Some makers claim an increase in sailing speed of up to 1 knot, but this seems hard to believe. Also, I am fearful that I will loose motoring speed. Can anybody shed a little light on how a feathering/folding prop is likely to affect the sailing and motoring speed of a Pearson 365? If you have installed a folding or feathering prop on a similar boat, would you do it again knowing what you know now? Any suggestions on make and model of prop would also be appreciated.
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Old 27-01-2011, 12:21   #2
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Originally Posted by Mike Sibley View Post
I need to replace the prop on my 1979 Pearson 365. As long as I am at it, I thought I might cnside a folding or feathering prop. However, such props are expensive and I am unsure how much I will gain on a boat like a Pearson 365. Some makers claim an increase in sailing speed of up to 1 knot, but this seems hard to believe. Also, I am fearful that I will loose motoring speed. Can anybody shed a little light on how a feathering/folding prop is likely to affect the sailing and motoring speed of a Pearson 365? If you have installed a folding or feathering prop on a similar boat, would you do it again knowing what you know now? Any suggestions on make and model of prop would also be appreciated.
Oops! Wrong fourm! Sorry!
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Old 27-01-2011, 13:48   #3
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Many of the folding props are aimed at the racing sailor who only cares about getting out of the marina. The performance of these props is poor in forward and sometimes non existant in reverse. Not a good choice for a cruising boat.

The feathering props are designed for real life engine use but at a very high price and often complcated maintenance. There are also some folding props that are better designed for performance under power but also at a price.

The claims of a knot of boatspeed just for the propellor alolne is subject to a whole lot of skepticism. They will give you slightly better performance but primarily on extreme low wetted surface boats. A boat like a Pearson 365 just isn't going to make a whole lot of difference. Not worth the cost unless you want to drop $3,000 or so into something that will give minimal return. Much better to invest in sails or sail handling equipment that will allow you to get the most drive out of your rig.

FWIW, sailed three Westsail 32s on 400 plus mile deliveries. Two had 3 bladed props and one had a two blade prop that was feathered behind the deadwood for minimal drag. The two boats with 3 bladed props had slighly better three day total miles than the two bladed prop. All three trips were under near identical conditions on a beam reach in force 4 conditions. These boats are the extreme for wetted surface but the P365 is closer to a Westsail than it is to a Farr 36.
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Old 27-01-2011, 15:04   #4
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I disagree with Roverhi. There was a very good article written in one of the British yachting magazines a year or so back on the theme "If you want to sail faster - buy a new propeller" which argued very convincingly that money spent on a feathering/folding propeller was a more cost-effective investment than money spent new or additional sails.

Secondly - we've experimented extensively with our own boat - a Cabo Rico NE400. She's 37' LOD, 34' LWL and in cruising trim displaces close on 30,000 lbs with a sail area of approx 680 sq ft. Not exactly a lightweight flier. Originally fitted with a three blade fixed propeller, we changed this for a Brunton Autoprop which was problematic. The Autoprop was then re-sized and tested again but finally discarded a season or two later for a 4 blade SPW Variprop which we have used for the last six or seven seasons. This has flat, feathering blades very much in the style of a Maxprop. I recorded detailed engine RPM v speed trials for each propeller and would be happy to send you the excel spreadsheet data to look at if you wish.

In terms of sailing ability we found that the feathering prop significantly improved performance throughout the wind speed range, but we notice it most in light airs when the boat moves more easily and when sailing flat out (that's about 9 knots for us!).

In terms of motoring it was probably as you expect. The fixed blade prop was best at maximum rpm (as that what most props are matched to). The Autoprop was very efficient at lower rpm but caused a lot of vibration which led to premature wear in the cutless bearing. The Variprop with its flat blades will never be as efficient at maximum rpm, but - as one can adjust the pitch - we have been able to tweak it so that it is actually slightly more efficient than the fixed prop at cruising rpm. We've lost in the region of three quarters of a knot at maximum rpm, but of course we've gained at least this when sailing.

In the end it's all a compromise, but our own experience would suggest that even a heavy cruising boat can achieve significant improvements in sailing speed whilst still maintaining an efficient motoring performance at cruising rpm.

One last point: yes a feathering prop is expensive and I was concerned that it would be easily damaged if we fouled it somehow. However, we've twice had rope around the Variprop which has stalled the engine (once so violently to the point where the engine wrecked all the mounts) but on each occasion the Variprop has been unscathed. I can therefore attest to it's robustness! (and no I have no affiliation to the company).
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Old 27-01-2011, 15:56   #5
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My Trimaran has a "Flex O Fold" folding prop. It is considered the best of the geared folding props. It is SUPER streamlined...

A few years back Practical Sailor, along with help from a test lab at MIT did comparisons of many props of equal size... (this is square inches of blade surface, NOT diameter).

What MIT found, was that in forward, the Flex O Fold was hands down the most efficient prop made, bar none! This included comparison to a Max Prop, and a "Michigan Wheel" fixed, three bladed prop!

They defined "efficiency" as the amount of thrust = boat speed, delivered at a given fuel consumption.

In reverse, the Flex O Fold was only so so. It was better than the old Martecs, but not nearly as good as the Max Prop. (Fixed props are pretty bad in reverse too.)

Besides the above, folding props VS feathering... have the advantage of being more slippery, cheaper, less complicated, and they don't snag crab pot lines when in sailing mode, like feathering ones do. The one advantage of a good feathering prop, is WAY better reverse thrust! If that is not an issue, the Flex O Fold is the way to go.

BTW... The article really debunked some myths too. size for size (= square inches of blade), a three bladed prop is NOT as good as a two. and the best would be a ONE bladed prop. The thing is that it wouldn't balance! The fewer blades the better, because one blade is a bit less in the propwash or the other, the fewer the blades.

Folks who go from a 15" two blade to a 15" three blade, and liked the results, have in fact gone WAY up in prop size, and their two blade always was too small for the boat / engine combination.

Many times there just isn't enough hull clearance to go up in diameter, (which is better than up in pitch), so a problem CAN be solved by switching to a three bladed prop. Given enough clearance however, (at least 2"), if you need more prop thrust, and the engine can still hit its max RPM, a larger TWO bladed prop is more efficient than the same blade surface sized THREE bladed.

Just thought I'd throw that "fun fact" in there,
Mark
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Old 27-01-2011, 16:37   #6
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A copy of the yachting Monthly article testing a variety of folding and feathering propellors can be found on the flex-o-fold website.

Folding Propellers - Flexofold

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Old 27-01-2011, 17:02   #7
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A copy of the yachting Monthly article testing a variety of folding and feathering propellors can be found on the flex-o-fold website.

Folding Propellers - Flexofold

Pete
Thanks for the link Pete. I hadn't seen that review before, but it's certainly comprehensive and the conclusions match our own experience.
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Old 27-01-2011, 19:13   #8
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If you opt for a prop with an overdrive feature you may actually gain both when motoring and when sailing. Also the models with continuous pitch work towards this end.

I would say the folding / feathering thing is a must for a racer and a welcome luxury for a long distance cruiser. Otherwise it is just luxury and if you can afford it you will probably go for it.

Make sure the option you take goes well with the prop aperture / offset you have there - not all boats have the space there that allows for a folding prop.

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Old 27-01-2011, 19:30   #9
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My Autostream feathering three blade (sold by Martec) has given me about .6 kt increased speed sailing over the old prop--about a 10% improvement--I do not recall what a Pearson 365 has around the prop--mine is in the open so i am guessing that that is about it. Nicest thing is being able to adjust it forward and reverse so that you get the right pitch in each--you can adjust this one externally and separately for forward and reverse. My stock prop was grossly over pitched and lugged the engine. Would have cost me many hauls and a lot of prop shop work to get the pitch right in a fixed blade prop. Maintenance is just greasing it every year or so. I consider it an important investment for cruising. I installed it myself--it is not complicated.
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