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Old 13-12-2013, 14:53   #31
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Re: Prop spinning under sail ???

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Originally Posted by Parmenter View Post


Seems quite obvious doesn't it, like dragging a bucket behind the boat.
I am surprised its even being argued.
Possibly because the reverse is sometimes true. For instance a helicopter auto-rotating falls much more slowly than it does with the rotors stopped.
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Old 13-12-2013, 15:02   #32
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Re: Prop Spinning under Sail?

Interesting point.... and also.... if you want to slow a big ship down you are better off going 'slow ahead' for a few minutes than just stopping the engine. Mind you 'slow ahead' involves controlled rotation as opposed to free wheeling.
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Old 13-12-2013, 17:16   #33
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Re: Prop spinning under sail ???

[QUOTE=onestepcsy37;1402437]i've got a perkins 4-108 with a velvet drive transmission and 3 bladed prop.

according to the velvet drive manual it's ok for it to spin while under sail. but it is noisy and i've often thought about just clamping a vise grip around the shaft and letting it jam up against the hull. the reason i haven't done that is because i'm afraid i'll forget to remove it when i need to use the engine...

Used a vice grip on our W32. Worked fine. The few times I forgot to take the VG off, it just released on it's own when the engine was put in gear. A pain to find it under the engine pan later, though. Scoring the shaft would be somewhere in the middle, if it should happen, and shouldn't be a problem as the stuffing box is usually well away from the area that the seal will ride on.

I'd be afraid of using a pipe wrench. Those things generate serious torque and bite harder as more force is applied, should the shaft turn. if the wrench didn't release.

Can't get at the shaft on the current boat so am practicing my knot tieing to see if it will work. Doing that had never occurred to me. Mahalo for the tip

Yanmar says not to lock their transmissions in gear. The noise of the spinning prop drives me crazy, though, so I do it. So far the transmission has survived a TransPac with it locked in reverse.
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Old 13-12-2013, 22:02   #34
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Re: Prop Spinning under Sail?

The extra speed of a free wheeling prop is nothing compared to the extra sleep on a passage from a stopped (quiet) prop. Been there, done that. _____Grant.
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Old 13-12-2013, 22:09   #35
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Re: Prop Spinning under Sail?

Interesting that a spinning prop is thought to have less drag when the opposite is normally true.
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Old 13-12-2013, 22:50   #36
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Re: Prop Spinning under Sail?

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Originally Posted by forsailbyowner View Post
you can buy an aftermarket shaft lock if your concerned about it.The velvet drive in my boat has been in service since 1976 with the prop spinning under sail. Dont sweat it. I like the sound of the gearbox spinnning, it means Im doing above 4kts. Id take this trans above any other given the performance of and longevity of the one I have. Same goes with the perkins, how many yanmars will be around after 37 years of service and over 10k hrs and still go oil change to oil change without having to add oil?
My Velvet drive in reverse when under sail will stop the prop from spinning, great when you need some sleep.
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Old 13-12-2013, 23:42   #37
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Interesting reading

http://www.catamaransite.com/propeller_drag_test.html
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Old 14-12-2013, 00:22   #38
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Re: Prop Spinning under Sail?

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Originally Posted by robert sailor View Post
Interesting that a spinning prop is thought to have less drag when the opposite is normally true.
Less drag is thought to have a spinning prop?
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Old 14-12-2013, 03:11   #39
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Re: Prop Spinning under Sail?

Some folk compare the drag of boat prop to that of a light aircraft prop but fail to account for the differences in basic design.

Light aircraft don't have a option to put in in neutral (there is no transmission) so when the aircraft prop is spinning (with the engine off), it is actually turning the engine over (and through compression of each cylinder). Also the only control of whether your aircraft prop will spin (windmill) or stop is via the pitch adjustment and that is another variable. It is normally considered that a spinning prop on an aircraft (with engine turned off) creates more drag than a stopped prop.

On a sailboat, the opposite is considered normal.
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Old 14-12-2013, 03:47   #40
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Re: Prop Spinning under Sail?

Well now I just learned something which is always nice!! My opinions are from my flying background and are not applicable in the water. Thanks for the post and the article.
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Old 14-12-2013, 07:28   #41
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Re: Prop Spinning under Sail?

You could have shown me graphs, charts,MIT study's etc all day long but show me a prop mounted on some pipe screwed to to some wood hanging off the side of a dingy with a scale BAM! debate over !You got to love it
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Old 15-12-2013, 15:05   #42
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Thumbs up Re: Prop Spinning under Sail?

Hi Everyone,

I want to thank you all for taking the time to reply. If it ever stops snowing here in Vermont I'll go out to the boat and check the transmission and see what kind it is. And I'll definitely check the transmission oil level. As long as having the prop spin isn't likely to cause damage to the transmission, I can live with the noise (I just make someone else sleep in the quarter berth when we're on passage.). My mind is definitely somewhat more at ease.

Thanks again!
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