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Old 10-14-2011
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To free-wheel or not?

We just spoke with an experienced Westerbeke engine/transmission distributor who told us that a boat will sail with less drag if the shaft is locked compared to free-wheeling. This seemed counter-intuitive. Has anyone confirmed this one way or the other? Thanks
Pete
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Old 10-14-2011
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General advice for a fixed prop is to keep the gear box in reverse, with the engine off, to keep the prop from moving. However, I always thought that was to keep it from cranking the transmission if being pushed by the slip stream, not necessarily a drag reducer.

For a feathering prop, keeping it in neutral allows the prop to feather, even though you might first stop it with reverse.
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Old 10-14-2011
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Quote:
Originally Posted by prroots View Post
We just spoke with an experienced Westerbeke engine/transmission distributor who told us that a boat will sail with less drag if the shaft is locked compared to free-wheeling. This seemed counter-intuitive. Has anyone confirmed this one way or the other? Thanks
Pete

Your "experienced dealer" is stuck with helicopter blade analogies that never translated well to fixed blade props traveling at 2-7 knots through water..

This has been dis-proven multiple times as related to sailboat props. MIT, University of Strathclyde, and YM Magazine have all tested this and all come to the same conclusion that free wheeling a fixed blade prop causes less drag.

I even went so far as to physically drag props through the water locked and unlocked. Free spinning has considerably less drag..

Prop Drag Test Movie - YouTube

If you have a Yanmar with Kanzaki box you do not want to lock it in reverse. Yanmar's recommendation is to let it free spin or lock it with a shaft brake.

With a Westerbeke and Hurth/ZF you can lock it or let it free spin . You'll have less drag with a fixed prop by letting it free spin.
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Old 10-14-2011
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Whoda thunk? Although I wonder if 25 pounds of pull means much with regards to a 10,000 pound sailboat.

The vibration of the free spinning prop bugs me sometimes though. In fact that's usually what makes me lock in reverse.
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Old 10-14-2011
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Quote:
Originally Posted by Maine Sail View Post
Your "experienced dealer" is stuck with helicopter blade analogies that never translated well to fixed blade props traveling at 2-7 knots through water..

This has been dis-proven multiple times as related to sailboat props. MIT, University of Strathclyde, and YM Magazine have all tested this and all come to the same conclusion that free wheeling a fixed blade prop causes less drag.

I even went so far as to physically drag props through the water locked and unlocked. Free spinning has considerably less drag..

Prop Drag Test Movie - YouTube

If you have a Yanmar with Kanzaki box you do not want to lock it in reverse. Yanmar's recommendation is to let it free spin or lock it with a shaft brake.

With a Westerbeke and Hurth/ZF you can lock it or let it free spin . You'll have less drag with a fixed prop by letting it free spin.
Thanks so much for the info and proof in form of movie We have a ZF manufactured transmission called a JS. The manual recommends leaving gear in Neutral or Forward. Most all dealers recommend Reverse?
Pete
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Old 10-14-2011
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I was always under the impression w/ the westerbeke on my cs36 that allowing the prop to freewheel, w/o the engine running, would damage the transmission. Don't remember if that was in the manual or the original owner told me that. I do know the shaft spinning while sailing drives me nuts.
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Quote:
Originally Posted by Ninefingers View Post
Whoda thunk? Although I wonder if 25 pounds of pull means much with regards to a 10,000 pound sailboat.

The vibration of the free spinning prop bugs me sometimes though. In fact that's usually what makes me lock in reverse.
It's relative to the drag of the boat, not its mass...
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Old 10-15-2011
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We have a Paragon tranny on our Perkins 4-107, the manual says it is OK to freewheel but as stated elsewhere, the noise will drive you nuts. I have a shaft lock that does the trick while underway. Lots of people get hung up on the gear overheating if let freewheel, but the heat comes from the engine driving the hydraulic pump and squeezing the oil when the tranny is in use, when freewheeling the clutches are disengaged and the gears are spinning in their oil bath. The Paragon we have does not have oil galleys to the bearings, every thing is just oiled by splash, bath or overflow.

Last edited by HorizonOI41; 10-15-2011 at 08:09 AM.
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Old 10-15-2011
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Quote:
Originally Posted by Maine Sail View Post
...
If you have a Yanmar with Kanzaki box you do not want to lock it in reverse. Yanmar's recommendation is to let it free spin or lock it with a shaft brake.

..
Not disputing that but really interested in more information. Can you post a link to that information if possible? The Kanzaki gearbox is the one that they are using on new models? That applies also to folding propellers?

It seems logical to me that a free spinning propeller creates less drag but it also creates unnecessary wear on the material and I have heard that it was prejudicial, something related with lack of lubrication. Can you comment on this?

Regards

Paulo
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Originally Posted by PCP View Post
Not disputing that but really interested in more information. Can you post a link to that information if possible? The Kanzaki gearbox is the one that they are using on new models? That applies also to folding propellers?

It seems logical to me that a free spinning propeller creates less drag but it also creates unnecessary wear on the material and I have heard that it was prejudicial, something related with lack of lubrication. Can you comment on this?

Regards

Paulo

Yanmar MSA .pdf


"Advisory Number: MSA08-003:

DATE February 8, 2008 Dealers and OEMs
TO: All Marine Distributors
SUBJECT: Gear in Neutral While Sailing All MODELS:

All Sailboat Engines

We continue to get questions regarding the correct gear position while sailing with the engine OFF. This advisory is issued as a reminder; Yanmar requires that if sailing with the engine OFF (not running) the transmission shifter must be in the neutral position or internal damage to the gear or sail-drive will result. This damage will not be covered by Yanmar’s Limited Warranty. Please instruct customers and dealers who deliver the sailboat to the customer, of the correct (Neutral) position for the marine gear while sailing.

If the customer desires that the propeller shaft not spin while sailing, either a folding propeller, shaft brake, or other suitable device may be used.
However, Yanmar accepts no responsibility for the selection, installation, or operation of such devices. Please also refer to Marine service advisory “MSA07-001_Yanmar Sail Drive Propeller Selection” for additional information.

If you have any questions regarding this advisory please contact a Customer Support representative."


The guy from Yanmar admitted that prior to 2008 they did not take much of a position either way in regards to reverse or neutral, hence the constant confusion on the forums when talking about Yanmar's.

This info does NOT apply to other engine makers!
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