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Old 21-10-2017, 12:39   #1
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Folding or Feathering Prop Advice

Hi all

After years of research and looking at several boats I finally pulled the trigger and bought a Broadblue 38 Prestige last summer.

Since it is a true blue water boat by design and well maintained, there is actually not so much which needs to be done, but as you all know, when one starts...

So one of the things I plan to replace are the props. She once had feathering props but they where stolen while she was on the hard, so now she's got the original fixed two blade props back on again.
She is somewhat overpowerded as she has got two 55 hp Volvo Penta engines with saildrives. With the current 2-blade props she makes 8 knots in flat water with 2'000 rpms (both engines on) and manouvering is basically done at idle speed. So from that aspect there is no need to get bigger props.

The only reason to replace the props is the drag and the constant wear on the sail drives due to the turning of the props when sailing.

I should have enough space between the saildrive and the rudder, so mounting folding props should be possible but I'm not sure if this is the best option?

Planned usage of the boat: full time livaaboard while cruising incl. ocean passages as well as coastal cruising. I like the simplicity of folding props vs. feathering ones, but a little worried over the open machanics and barnacle growth. In general I prefer simple solutions, but the drag of a fixed prop seems to be bad enough to justify the extra cost and complication of a prop with moving parts?

Do you have suggestions of which brand and type of prop I should choose? Especially long term experiences in tropical waters would be great!

Or even if I should just leave the fixed ones on?

cheers Jan
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Old 21-10-2017, 13:11   #2
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Re: Folding or Feathering Prop Advice

This has been debated many times here on CF, so some searching will give you LOTS of opinions. Some of them are valid.

But in a nutshell, here are the facts:

Folding
Less expensive
Simpler construction
More efficient due to twist in blade design
Some designs don't do well in reverse
Pitch is fixed and not adjustable
lowest drag sailing


Feathering
More expensive
Complicated mechanically
Inefficient blade design due to zero twist
High thrust at stall in both forward and reverse
Pitch adjustable, some designs in the water.
Drag less than fixed but more than folding.
Some designs seem to need rebuilding after relatively low hours of use

A look at the tests that were done at MIT some years ago show unbiased comparisons between several designs of each type... highly recommended reading.

In your place, I'd fit Flex-O-Fold three blade folders, on the basis of personal experience covering both types and several makes of props.

Jim
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Old 21-10-2017, 13:43   #3
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Re: Folding or Feathering Prop Advice

I've been all though this decision have had a boat with a MaxProp and a boat with a Flex-O-Fold.

Get the Flex-O-Fold!!
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Old 22-10-2017, 03:48   #4
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Re: Folding or Feathering Prop Advice

Yes I have read the MIT test already, but this just covers the direct comparison. I was more after practical long term experiences in terms of durability, trouble-free operation and as little maintenance as possible
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Old 22-10-2017, 09:41   #5
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Re: Folding or Feathering Prop Advice

I've sailed decades and thousands of miles using both folding and 3-blade feathering props, though never a flex blade. My choice would be the MaxProp 3-blade feathering.

With regard to folding props: Over time, there is considerable wear on the pins that attach the blades to the hub. Reverse action is poor, both because the blades are spinning backwards in respect to their design and they do not work effectively at idle speeds.

With regard to feathering: I disassembled and serviced the props once a year. Never had a maintenance issue. In that the blades actually reverse when in reverse gear, their reverse performance is better than that of fixed blade props.

I used Max Props on two of my boats, each for more than a decade, and never had a problem.
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Old 22-10-2017, 09:50   #6
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Re: Folding or Feathering Prop Advice

Two years on, we are delighted With our Flexifolds.
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Old 22-10-2017, 09:57   #7
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Re: Folding or Feathering Prop Advice

I have never had a problem in reverse with my Flex-O-Fold folding prop and it does seem any different that my last boat that have a Maxprop. I know that this reverse thing is something Maxprop likes to say, but testing doesn't really support it.

And I'm more interested in going forward anyway.
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Old 22-10-2017, 10:25   #8
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Re: Folding or Feathering Prop Advice

This boat has had flexofolds since new 2011. Never had a problem, pins are fine, the zincs wear down pretty quick in the Caribbean, good for only a year, but can be changed underwater if necessary. Reverse gear is adequate but not brilliant. Other point may be that lobster pot lines may catch on blades that are not folded. When using power and a lobster pot threatens we put the relevant engine in neutral, haven't hooked one yet.
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Old 22-10-2017, 10:27   #9
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Re: Folding or Feathering Prop Advice

Try putting the gear into reverse to stop the props from spinning. Makes a big difference on our cat with Max Props.

Cheers,
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Old 22-10-2017, 10:36   #10
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Re: Folding or Feathering Prop Advice

Quote:
Originally Posted by jdazey View Post
Try putting the gear into reverse to stop the props from spinning. Makes a big difference on our cat with Max Props.

Cheers,
No shaft locking feature other than the transmission?
I would think that would put strain on the transmission without lubrication.
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Old 22-10-2017, 10:55   #11
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Re: Folding or Feathering Prop Advice

To either feather a Max Prop or to fold any folding prop, one only needs to momentarily put the transmission in reverse.

We put ours back in neutral as soon as it's folded, and can hear the difference.
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Old 22-10-2017, 11:04   #12
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Re: Folding or Feathering Prop Advice

Quote:
Originally Posted by CruiserAD View Post
Yes I have read the MIT test already, but this just covers the direct comparison. I was more after practical long term experiences in terms of durability, trouble-free operation and as little maintenance as possible


Your description is a fixed prop, anything with moving parts will detract from your statement, perhaps a Campbell Sailor to reduce drag somewhat.
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Old 22-10-2017, 11:20   #13
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Re: Folding or Feathering Prop Advice

I originally fitted a two blade folder on my Parker 27 three years ago which increased my speed under sail by almost a knot and under power could easily achieve hull speed, however, I moved from my swinging mooring to a double pile mooring two years ago, which required that I be able to stop smartly abeam my berth as it was at 90 degrees to the prevailing wind which nearly always blew me off (I had another boat alongside that had the upwind berth) Many times I had to go round again as I could not stop quickly enough with the folding prop and if I approached too slowly, my bows would be blown off and miss my mooring (narrow channel as well). In the end had to change to a more expensive feathering prop (featherstream) which solved the problem. Don't notice any difference in my sailing speed but have to push the engine harder to reach hull speed (6.5 kts) and cruising speed of 5.5kts requires 2500 rpm. Otherwise, it's a great prop. Tried a higher pitch cassette but the engine smoked at 2750rpm which was the highest I could achieve and it is supposed to be able to achieve 3400rpm (Yanmar 2GM20) but I am reluctant to push it that far as it's already done over 5000hrs. All in all I would prefer the folder but if you need stopping power, go for a feathering prop.
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Old 22-10-2017, 13:47   #14
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Re: Folding or Feathering Prop Advice

Quote:
Originally Posted by Jim Cate View Post
Feathering
.
.
Inefficient blade design due to zero twist.
.
Pitch adjustable, some designs in the water.
Not all feathering props are inefficient, or allow changing of pitch. Probably the oldest design out there is the Luke, which dates back nearly a century. It has efficient curved blades and is a simple, sturdy construction in bronze. The stops are machined into the bronze - they can be altered by the factory or a good machine shop but not by the owner and certainly not in the water. The downside is that it needs to have a low viscosity grease pumped into the hub occasionally, which can be done underwater.

For racers it is important that a prop have the absolute least drag under sail, even at a substantial loss of performance under power, which is the case for most feathering and folding props. For cruisers I feel that a small loss of performance under sail (i.e. much better than fixed but less than other feathering/folding props) is acceptable for a large increase in efficiency under power, which is what the Luke offers.

Automatic Feathering Propellers, P. E. Luke. Full Service Boatyard, Boothbay, Maine.

Greg
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Old 22-10-2017, 13:56   #15
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Re: Folding or Feathering Prop Advice

The sure expensive.

The folding prop on my Nordhavn ''get home" engine consisted of two floppy blades. Nothing expensive nor complicated. What surprised me was, when I took the boat of the water, the prop was clean.
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