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Old 13-07-2014, 11:08   #1
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Reverse Gear while Sailing?

I just installed a 2qm15 yanmar in my boat and went sailing for the first time. It has a kbw10 transmission. Question is should I leave the transmission in neutral or reverse when the engine is off and the boat is under sail. I have the service manual but I can't find any reference to this. Thanks
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Old 13-07-2014, 11:27   #2
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Re: Reverse Gear while Sailing????

I've sailed on a lot of boats with a lot of different people and have heard conflicting points of view: a) in reverse creates less drag and improves boat speed, b) in reverse will cause damage to the propulsion system, c) depends on whether it's a fixed, folding, or feathering prop.

I too am curious what the correct answer is.
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Old 13-07-2014, 11:34   #3
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Re: Reverse Gear while Sailing????

If your prop is auto-rotating, depending on the type of transmission you have, putting it in reverse will stop the prop from turning, which will in turn decrease drag and wear on your bearings.
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Old 13-07-2014, 11:39   #4
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Re: Reverse Gear while Sailing????

Believe Yanmar says to leave the transmission in neutral. Nice in theory but a real pain in real life. Tried neutral for a short while on the sail to Hawaii but the noise of the spinning prop drove me crazy so put transmission in reverse. So far, no signs of any problems.
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Old 13-07-2014, 12:07   #5
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Re: Reverse Gear while Sailing?

I sometimes put my Yanmar 3GM with V drive types in reverse with no ill effect.
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Old 13-07-2014, 12:27   #6
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Re: Reverse Gear while Sailing?

Most all engine/transmission manuals have instructions for how they can/should be set when underway and not in use. This will differ depending on how each is lubricated and the type of clutch used.

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Old 13-07-2014, 12:33   #7
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Re: Reverse Gear while Sailing?

a) It depends on you transmission. Contact transmission manufacturer for the right answer.

b) A prop left to freewheel creates less drag tan a prop locked in, you can find info on this across the web. This is weird as I know that any wheeling element (e.g. an angling bait) creates more drag when wheeling rather than when locked (say fouled by weed). Odd.

E.g. Our transmission on an old Volvo engine can either be reversed or else you are supposed to start the engine every 10 hours and then you can let it freewheel in the in-between periods.

b.
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Old 13-07-2014, 15:04   #8
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Re: Reverse Gear while Sailing?

The amount of drag created by a non-spinning prop is minimal. I doubt if it could be measured unless you are sailing a non-ballasted open cockpit day sailer. Most modern transmissions are not subject to output shaft bearing wear and you can allow to freewheel if you want. You could also put the transmission into forward if you wish. You would have to be going very very fast to accidentally push start the boat!
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Old 13-07-2014, 15:12   #9
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Re: Reverse Gear while Sailing?

Quote:
Originally Posted by crazyoldboatguy View Post
The amount of drag created by a non-spinning prop is minimal. I doubt if it could be measured unless you are sailing a non-ballasted open cockpit day sailer. Most modern transmissions are not subject to output shaft bearing wear and you can allow to freewheel if you want. You could also put the transmission into forward if you wish. You would have to be going very very fast to accidentally push start the boat!
Never leave a Hurth ZF in forward when sailing!Neutral or preferably reverse.
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Old 13-07-2014, 17:27   #10
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Re: Reverse Gear while Sailing?

Quote:
Originally Posted by crazyoldboatguy View Post
The amount of drag created by a non-spinning prop is minimal.(...)

Please link to relevant sources. I must read up some.

According to tests conducted, independently, by YM and Segeln:

"At 5 knots, a fixed three-blade prop with its shaft locked creates almost half as much drag as the entire hull."

and

"The hull resistance curve for the Océanis 323 was calculated for YM by the Wolfson Unit, at the University of Southampton, using data from the
Delft University Systematic Series. The propeller drag curves are based on data from SSPA Maritime Consulting, using Volvo S-drives. This data was
verified by YM’s on-the-water drag test."

Roughly the same was found by Segeln team, who conducted real life experiments towing props.

Congrats,
b.
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Old 13-07-2014, 18:29   #11
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Reverse Gear while Sailing?

A spinning prop should create more drag than a stopped one, this is very easy to demonstrate in an aircraft with the engine off, simply establish a glide at the best glide speed, look at the VSI and note rate of descent, then slow the airplane until the prop stops and re-establish best rate of glide speed, note how the rate of sink is less.
Energy is used in spinning the prop, this energy of course comes from your sails, there is no free lunch.

Stopped or spinning, the drag is rather large, just ask anyone who owns a feathering prop

BTW, I don't
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Old 13-07-2014, 18:54   #12
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Re: Reverse Gear while Sailing?

As others have said it all depends on whether the reduction gear is self lubricating (which most of the new ones are today due to popularity of twin props).

Freewheeling in neutral seems to be the most common practice and I believe (in the water) ... spinning causes less resistance in the cavitation flow than a fixed 3 bladed prop acting as a drag through the sea.
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Old 13-07-2014, 19:07   #13
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Re: Reverse Gear while Sailing?

Quote:
Originally Posted by a64pilot View Post
A spinning prop should create more drag than a stopped one, this is very easy to demonstrate in an aircraft with the engine off, simply establish a glide at the best glide speed, look at the VSI and note rate of descent, then slow the airplane until the prop stops and re-establish best rate of glide speed, note how the rate of sink is less.
Energy is used in spinning the prop, this energy of course comes from your sails, there is no free lunch.

Stopped or spinning, the drag is rather large, just ask anyone who owns a feathering prop

BTW, I don't
Not according to Maine Sail's tests:

Propeller Drag under sail, Article
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Old 13-07-2014, 19:11   #14
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Re: Reverse Gear while Sailing?

Yeah, I'm pondering that, I can't understand why a stopped prop is less drag than a turning one.
I've tried and on my boat I can't tell the difference, but then again I'm no racer, and an IP is no performance boat either.
IP says put it in reverse, so I do.
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Old 13-07-2014, 19:22   #15
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Re: Reverse Gear while Sailing?

Been doing a little pondering.
Maybe the difference is that aircraft props and helicopter blades are a very high aspect ratio airfoil, and boat props aren't, so it's an apples to oranges thing, maybe?
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