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Old 11-08-2016, 14:56   #16
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Re: Prop Freewheeling or dragged?

Several replies mention there is less drag when free wheeling. There is an article by Nigel Warren Body which is based on tests undertaken.
Basically in most cases there is less drag if the propeller is locked but there are a lot of variables.
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Old 11-08-2016, 15:29   #17
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Re: Prop Freewheeling or dragged?

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Originally Posted by Uplander View Post
Several replies mention there is less drag when free wheeling. There is an article by Nigel Warren Body which is based on tests undertaken.
Basically in most cases there is less drag if the propeller is locked but there are a lot of variables.
You may want to look at the University of Strathclyde Study as well as the MIT study which both specifically focused on sailboat props.. There are even videos that show nearly double the drag when locked vs. free spinning plus I believe a UK magazine also did a study. They all found the same thing with sailboat props, locked = more drag..
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Old 11-08-2016, 15:36   #18
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Re: Prop Freewheeling or dragged?

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Originally Posted by Uplander View Post
Several replies mention there is less drag when free wheeling. There is an article by Nigel Warren Body which is based on tests undertaken.
Basically in most cases there is less drag if the propeller is locked but there are a lot of variables.

Advertorial by the makers of a shaft lock?

Those "tests" are theoretical calculations based on "cavitation tunnel" data and shaft friction. And his logical in applying that data is severely flawed as well.


I much prefer the results of real world tests which have been discussed here many times previously and which are fairly conclusive that freewheeling results in less drag. Rather than regurgitate all the information, here's a link:

Spinning Props
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Old 11-08-2016, 15:40   #19
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Re: Prop Freewheeling or dragged?

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Do you have a link to that service bulletin? Usually they state to leave them in reverse (for Yanmars anyway)
Here ya go: http://www.catamaransite.com/files/Y...al_Sailing.pdf

And from the Volvo 22 Series manual:
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Old 11-08-2016, 15:49   #20
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Re: Prop Freewheeling or dragged?

All manual transmissions I have seen freewheel ok. Most hydraulic transmissions that only lube the back bearing by pressure don't. Manufacturer has the last word.
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Old 11-08-2016, 15:50   #21
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Re: Prop Freewheeling or dragged?

Do a simple test under sail on your boat. Speed when freewheeling vs speed when locked in reverse. It may take 4-5 data points because you are testing with variable wind speed, but you should get an idea of which is less drag.

If freewheeling is faster and you can put up with the noise and the wear on your stuffing box and transmission, go for it. I think Yanmar advocates freewheeling because their transmissions tend to get stuck in reverse, but velvet drives advocate the opposite because their transmissions don't get proper lubrication when freewheeling.
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Old 11-08-2016, 18:30   #22
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Re: Prop Freewheeling or dragged?

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Well never Fwd, but read your manual, mine says to lock the prop by putting in reverse, but most I believe want it free wheeling, there is less drag freewheeling but sometimes noise.
Do not tell a gyrocopter pilot that there is less drag freewheeling.
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Old 11-08-2016, 18:40   #23
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Re: Prop Freewheeling or dragged?

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Do not tell a gyrocopter pilot that there is less drag freewheeling.

I think ambulances should always be required to follow gyrocopters.


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Old 11-08-2016, 19:10   #24
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Re: Prop Freewheeling or dragged?

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Do not tell a gyrocopter pilot that there is less drag freewheeling.
I wouldn't dream of telling a gyrocopter pilot that there is less drag freewheeling a gyrocopter or helicopter rotor or an aircraft propeller.

But you are comparing a totally different profile and medium.

I will confidently tell a gyrocopter, helicopter or fixed wing pilot that there is less drag freewheeling a typical boat propellor in water.

And I have personally freewheeled helicopters rotors, fixed wing props and boat propellors (but I admit I've never flown a gyrocopter).
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Old 11-08-2016, 20:05   #25
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Re: Prop Freewheeling or dragged?

Well it seems I may be wrong. Not actually admitting it but close!
Yachting Monthly has an article which says "let it spin".
Lock your prop, or let it spin?
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Old 25-08-2016, 10:42   #26
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Re: Prop Freewheeling or dragged?

I think the mnfr. of engine is irrelevant , what is relevant is the mnfr of the g / box - my Beneteau 473 has a Z F g/box and they state that the G / Box must be locked by putting the g / lever in astern when sailing , it also, on long distance sailing , must save wear on the cutlass bearing and the propshaft seal . Fair winds Garth
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