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Old 28-08-2009, 18:17   #31
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The optional way is to lock the prop and then lift it out from the water. Possible with an outboard.

(Once off the water you can unlock it again).

;-)
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Old 29-08-2009, 07:40   #32
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Thanks Maine Sale for sharing your results. They appear definitive.

And, having worked in the MIT hydrodynamics lab (back in the day), I can say your experimental apparatus looks to be as carefully thought out and controlled as any of the experiments we did there at the time (I worked on the drag effects of fillet size at the keel-hull interface, with the data going into the VPP program that was just being developed at the time).

Good work with clear cut results!
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Old 29-08-2009, 14:36   #33
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Doesn't it depend on the transmission???

The factor that we seem to have strayed from in this discussion, is that different TRANSMISSIONS can be damaged by freewheeling, while some cannot.

For example a Borg Warner "VelvetDrive", a very common marine transmission, is hydraulically operated, and with the engine not turning, it doesn't matter where the shift lever is, the prop will free-wheel because the clutches will not be engaged. Borg Warner says that freewheeling at sailboat speeds won't harm the transmission

The typical transmission on older small Yanmars, for example, should have been locked in gear when sailing, since it says in the operation manual that the transmission lubrication did not work when the engine was not turning the input shaft, and the transmission could actually be damaged by allowing it to turn while sailing.

I think that the free wheel vs. fixed debate is one thing, but whether an individual boat owner should free wheel vs. lock the prop is a matter of transmission design, and not always a matter of personal choice.

Just wanted to bring that up, since it seems we haven't mentioned that in this discussion
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Old 31-08-2009, 13:34   #34
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Quote:
Originally Posted by jlogan View Post
The typical transmission on older small Yanmars, for example, should have been locked in gear when sailing, since it says in the operation manual that the transmission lubrication did not work when the engine was not turning the input shaft, and the transmission could actually be damaged by allowing it to turn while sailing.
Agreed, some transmissions share an oil sump with the engine and must be locked for sailing. However, how old a Yanmar are you talking about? I have 1985 1GM10 engines which work great and the original manuals for the engines as they came with the boat.

The manual states clearly to freewheel the props.
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Old 02-11-2009, 04:16   #35
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I was so taken with these definitive results, with Main Sail's permission, I added his prop drag test to my website. Whenever we get clear cut results on a controversial issue I feel it should be shared with the sailing community.

Main Sail is now a published author!

Propeller Drag Test
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Old 26-04-2011, 20:19   #36
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Re: Prop Shaft Spinning When Sailing

Has anybody here rebuilt their KH-18?
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Old 26-04-2011, 22:08   #37
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Re: Prop Shaft Spinning When Sailing

Thanks for that information Tropic Cat. I have twin 72hp perkins on my Motorsailer and have wondered about this. Mine automatically free wheel because of the BW velvet drive trannies. I had considered putting a brake on them, but now with the results shown I will forget that idea. I often motor with only one engine running or motorsailing that way. I only use two engines when entering or leaving a slip in a marina, so one side is most always freel wheeling.
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Old 26-04-2011, 22:49   #38
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Re: Drag...

Quote:
Originally Posted by Maine Sail View Post
...
I spent a few late nights in the barn, over the winter, listening to good tunes and plugging away on this design. ...
Wow... Thank you for your amazing efforts and well thought out experiment.

Chris
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Old 27-04-2011, 05:56   #39
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Re: Doesn't it depend on the transmission???

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Originally Posted by jlogan View Post
.

For example a Borg Warner "VelvetDrive", a very common marine transmission, is hydraulically operated, and with the engine not turning, it doesn't matter where the shift lever is, the prop will free-wheel because the clutches will not be engaged. Borg Warner says that freewheeling at sailboat speeds won't harm the transmission
That begs the question about using the max prop where a locked shaft is intially needed to get the blades to feather. I supose that the engine should be put in reverse while still running(to get the blades to reverse) and then turned off so that when sailing the flow of water will force the blades to feather.
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Old 27-04-2011, 06:20   #40
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Re: Prop Shaft Spinning When Sailing

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Originally Posted by Waterwayguy View Post
Damon and Dave, Hello from Chuck and Susan on Sea Trek. We are in Clear Lake. Sea Trek has a Yanmar 4JH3E with a different transmission than yours. But we have let the prop freewheel for several thousand miles and no issues at all. We too can here it but it lets us know what speed we are sailing by the sound it makes. Hope you guys are enjoying Panama.
I'm in agreement with the Sea Trek crew regarding the freewheeling. We also have a Yanmar 4JH3E, but still the Kanzakee transmission, and freewheeling is not a problem. On the other hand, I would not characterize the ability of forces to turn the prop, when in either gear, to indicate that the transmission is about to fail.
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Old 27-04-2011, 06:23   #41
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Re: Prop Shaft Spinning When Sailing

ALL sailboats can benefit from a feathering or folding prop, and on cruising boats, the benefit is often overlooked. Our Flex O Fold folds properly when freshly greased, but later, it sometimes tends to stay open and freewheel when I shift into N to sail. If I am not yet under sail, I slow to 1 or 2 knots, hit R, and it folds. Then shut it down. If underway sailing, I head up into the wind, ALMOST to being in irons, click it into R and then back to N, (@ low RPM), then fall off and resume sailing. Then shut it down. Only takes about 5 seconds... M.
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Old 27-04-2011, 06:33   #42
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Re: Prop Shaft Spinning When Sailing

I have the same whirring noise with my 3GM30F. It is not the noise that bothers me but the wear created when parts are moving. Motion over long periods creates wear. The cutlass bearing, seal, and internal tranny parts must be experiencing wear when they are moving for no good reason. If there were a way to safely brake the shaft at the coupling, I would do it. The boat has a 2 bladed wheel which could be set vertically behind the hull by a mark on the coupling. In this position, it would create little drag. For long trips, maybe a light piece of twine, wrapped around the shaft side of the coupling or a small dowel wedged in the bolt heads would stop it from rotating but break easily should the motor be needed quickly. ????
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Old 27-04-2011, 16:00   #43
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Re: Doesn't it depend on the transmission???

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Originally Posted by lancelot9898 View Post
That begs the question about using the max prop where a locked shaft is intially needed to get the blades to feather. I supose that the engine should be put in reverse while still running(to get the blades to reverse) and then turned off so that when sailing the flow of water will force the blades to feather.
I have an autostream feathering prop, and the instructions for feathering are to give some gas to ensure boat speed is fast enough to feather, shut down engine (while still in forward gear or neutral), then put the transmission in reverse for a few seconds to allow the prop to feather. You can then place the transmission in neutral, though I don't suppose it matters so much at that point as the prop is feathered and there's no real stress on the system. Seems to work well.
Chris
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Old 27-04-2011, 16:16   #44
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Re: Prop Shaft Spinning When Sailing

some of the leaky teaky-ites have spoken of placing a braking mechanism on their trannies--at the woodruff key. i havent noticed any problem from mine while sailing-- last time we placed it into reverse--i have a PERKINS 4-108, as many leaky teakies do-- some have yannies, some lehmans, isuzu.. depends on personal taste, as far as i can see. on ours, isnt like the drag is gonna make much difference--- ours are very nicely heavy displacement boats....and no one has mentioned problems with tranny while freewheeling.
and i really dont believe a folding prop is gonna be much of a plus on my brick..LOL...i understand there isnt any room for it in my opening between the hull and rudder.....
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Old 13-05-2011, 12:40   #45
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Re: Prop Shaft Spinning When Sailing

My 77 jeanneau had a rotor on the shaft and a small manual like caliper, to lock the shaft. red
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