Are folding props worth it?

[a64pilot]

Originally Posted by Zzmeyer

Attachment 195163



The above shows the results from the Yachting Monthly prop walk test. Note that one fixed prop is the best, the standard one is only so so. I've read that the feathering prop is the best in reverse because the leading edge is generally reversed when you put it in reverse making it more efficient than a reversing fixed prop that has its trailing edge leading. This would likely affect prop walk.

No, it’s that most feathering props blades are just flat plates, they have no blade twist nor an airfoil shape, both of course increase efficiency, but when a normal fixed prop is spun backwards neither the blade twist or more importantly the airfoil shape is of any use because of course the flow of water is backwards, so you lose any increase in efficiency that you had from those attributes, actually its working against you.
Most feathering props being flat plates don’t lose those attributes because they didn’t have them to start with.

Flat plates as a propellor is inefficient, people don’t like to accept that, but it’s true, that most feathering props are less efficient in producing thrust. Compared to other designs.
They will argue that until the cows come home, but it’s either accept that flat plates are inefficient or accept that all other propellor manufacturers who make props with airfoil shapes and blade twist are fools, cause a flat plate will work just as well.

[zboss]

I always thought prop walk was a virtue for docking and maneuvering in tight spaces but since we switched to a feathering JProp our low speed maneuvering has gotten much much better. The boat handles exactly the way you would expect it to handle and there is no comparison to our old Michigan Wheel fixed three blade.

Reversing is so much easier without the tendency of the boat to go off in a random direction.

We can still get prop walk at very high revs if we need it but so far we haven't.

[Jammer]

There are three facts to consider regarding the Yaching Monthly analysis:


1. The props tested were not of identical size or pitch, with diameters of 15, 15.5, 16, and 17 inches, and pitches of 11, 11.5, and 12 inches. The small difference in the test results could be explained as much by these differences in size and pitch as by the inherent performance of the various designs. Due to differences in blade twist among the designs and differences in where pitch is measured on a twisted blade, the effective pitch of various designs may have differed even when the same pitch was quoted by the manufacturer.



2. The fixed prop used as a reference may not have been the best prop for the vessel. The article does not state its size or pitch. The text of the article indicates that the best-performing folding prop -- which outperformed the fixed prop -- ran at significantly lower RPM than the fixed prop, indicating that there was a difference in pitch large enough to affect results.



3. The vessel used for testing had a 2.6:1 forward and 3:1 astern gear ratio. The test results may have been different had a gearbox been used that had the same ratios forward and astern.


For these reasons I would not consider some of the small differences in performance reported in the article to be meaningful.

[longjonsilver]

Here is the cause of prop walk:

http://www.castlemarine.co.uk/propwalk.pdf

jon

[Adelie]

My preference is for an outboard.

Even less drag than a folder since it doesn’t even need a prop strut.

Doesn’t need a bow bow thruster, probably as manoeuvrable as an inboard with a bow thruster.

Easier to do repairs, pull it into the cockpit no problem. Need professional help, take it to the shop, no fees for a dockside visit.

The only downside is gas mileage, but I’m keeping my eyes open for a diesel outboard.

[Zzmeyer]

Jammer - totally correct. I couldn't find the German sailing magazine article, but its results were a fair amount different. I have little experience with a fixed prop as I wouldn't have one based on sailing performance. I've quite a lot of experience with Martec, Maxprop and Flexofold and I find both of the latter to be great. Maxprop backed better. Both were reliable and effective pushing the boat. But even with that I've had the props on different boats so a perfect comparison isn't possible.

[alctel]

Firstly, not all props should be left 'locked' while sailing, my Yanmar 2qm20 transmission explicitly says to leave it in neutral while sailing. Check your manual.

Secondly, a lot cheaper option than the folding/feathered is a campbell sailor prop. Fixed three blade, but the drag is a lot less than a standard 3 blade. Only downside is any fouling on it kills your motoring speed.

http://www.westbynorth.com/campbell-sailer/

[longjonsilver]

From the aforementioned article:

Prop walk is caused by the angle of the propeller shaft to the water surface; if there is no angle, then there is no prop walk. For an increase in either the diameter or pitch of the propeller the effect is increased.

[a64pilot]

Originally Posted by longjonsilver

From the aforementioned article:



Prop walk is caused by the angle of the propeller shaft to the water surface; if there is no angle, then there is no prop walk. For an increase in either the diameter or pitch of the propeller the effect is increased.

I measured the driveshaft angle on my boat and I believe it’s three degrees, which of course is almost non existent, however with the fixed prop, the prop walk is enormous.

[a64pilot]

Originally Posted by Adelie

My preference is for an outboard.

Even less drag than a folder since it doesn’t even need a prop strut.

Doesn’t need a bow bow thruster, probably as manoeuvrable as an inboard with a bow thruster.

Easier to do repairs, pull it into the cockpit no problem. Need professional help, take it to the shop, no fees for a dockside visit.

The only downside is gas mileage, but I’m keeping my eyes open for a diesel outboard.

The efficiency difference between a good modern fuel injected out board and a Diesel is almost non existent, just as it is with some modern automobile engines.
Then take the weight into account and it’s likely the fuel injected gas motor may come out ahead.

[Jammer]

Originally Posted by Adelie

My preference is for an outboard.
...
The only downside is gas mileage

I have one.


Downside of an outboard:

1. Uses up half the transom, with consequences for ability to have a windvane, davits, swim platform, etc.
2. More susceptible to collision damage, particularly from locks, bridges, sea walls. Not feasible to fender the stern, at all, in an emergency
3. None have large enough alternators to provide useful charging of a house bank
4. The engine is relatively unprotected when motoring in a following sea, can easily be flooded in heavy weather
5. Susceptible to theft. No one will ever steal your inboard
6. Even the best designs have trouble getting the prop deep enough to remain fully under water in heavy seas

There are other problems that vary from one design to the next. Some outboard installations are extremely well thought out and have steering linkage to the rudder and remote throttle/shift controls that make them easy and intuitive to use. Mine is awkward in tight spots because it is tiller steer and hard to reach from the cockpit -- I end up with the rudder tiller in one hand and the motor tiller in the other.


But the newer outboard do very well in terms of noise, fuel economy, emissions, and ease of repair. It's great knowing that I can replace everything mechanical -- engine, transmission, prop, fuel system, the works -- for under $2500 including labor. I see larger outboards on MacGregors but not on larger sailboats. Not sure why, most of the rest of the boating industry has embraced them, even on larger boats.

[nhschneider]

We recently completed an 8-year, 49,000-mile circumnavigation with a Gori 3-blade folding prop connected to a Beta Marine 90hp engine with a ZF 45A transmission with a 2.5:1 reduction.

At 1,400 RPM, in calm conditions, we'd motor at 5.5-6 knots and burn .89 gallons per hour - not bad for a 40,000-pound, 48-foot ketch.

We never had any problems with the prop. Quite the opposite. We loved it.
We found the 2-speed feature to be especially helpful and with the prop in the appropriate attitude, I can back the boat up with a lot of confidence. We did have to replace the blade stops a few times but that's easy to do even underwater.

Fair winds and calm seas.

[Grumpy500]

I would never have a folding prop. Over the years I have seen many of them fail. Blades have falen off they have ceased up. You find out there is a problem just when you dont need a problem. Dont chance it. Stick with a good well designed fixed prop.

[DefinitelyMe]

We went from a standard 3-blade to a folding 3-blade. We get at least 1/2 a knot in decent wind conditions, but the real value is in being able to continue sailing when the winds are really light. We couldn't sail in less than 8 knots before, now we're good (on a reach) down to 5.

[cygnus]

I have a 1975 Pearson 10 Meter. Yanmar 2 GM20 F Feathering prop. I was told by a prop man when sailing put her in reverse and the prop will feather vertical so there won`t be any drag. Hope this helps. I was going to go with a fixed 3 blade prop for more power but with the price and drag combined I decided to be satisfied with what I have. Hope this helps.