free spinning shaft makes whirring noise

[bradandnatalie]

Hello all.
I have recently fitted new 3ym30ae Yanmars to my catamaran. These replaced the 3hm35f Yanmars that I bought it with. The older engines has the KBW10 gear boxes and when sailing you could put the gear in reverse and stop the shafts from spinning. The new gear boxes don't allow for this and the manual clearly states that the warranty will be void if the gear is not left in neutral when sailing. The problem is around 5 to 6 knots it's quite noisy with the spinning whirring sound. Is this normal or does anyone have any suggestions that would not void my warranty. The props are 3 bladed fixed and I'll not be replacing them. Thanks very much.

[senormechanico]

Imho, you can't get there from here with your parameters.

[admiralslater]

The only option would be a shaft break of some type . But then the turbulence wouls be gruesome. Not sure why you dont want to change props . Kiwi maybe

[billknny]

There are only two options:

A folding or feathering prop, or a shaft brake.

Either would be a good investment, with the feathering prop a better idea. The rotating shaft does wear on bearings, seals, packing glands, etc...

But since you are putting prop change off limits, its shaft brake or WHIRRRRRRRRRRRRR

[senormechanico]

There is a third option.
Sell the boat, buy a condo.

[Uncle Bob]

Originally Posted by bradandnatalie

Hello all.
I have recently fitted new 3ym30ae Yanmars to my catamaran. These replaced the 3hm35f Yanmars that I bought it with. The older engines has the KBW10 gear boxes and when sailing you could put the gear in reverse and stop the shafts from spinning. The new gear boxes don't allow for this and the manual clearly states that the warranty will be void if the gear is not left in neutral when sailing. The problem is around 5 to 6 knots it's quite noisy with the spinning whirring sound. Is this normal or does anyone have any suggestions that would not void my warranty. The props are 3 bladed fixed and I'll not be replacing them. Thanks very much.

https://www.yachtingmonthly.com/gear...let-spin-29526 .Why would you lock it? This is just one of the tests that confirm a locked prop creates more drag therefore slows the boat more than a spinning one.(there are others) Any wear on the transmission would be minimal at worst.

[admiralslater]

Uncle bob the consern was the noise and the warranty

[Uncle Bob]

Originally Posted by admiralslater

Uncle bob the consern was the noise and the warranty

Fair enough, warranty requires that prop be allowed to spin so a given, noise usually is not that loud, but if it is excessive then something is amis. Ballance perhaps? The other consideration may be sound insulation within the engine compartments.

[s/v Moondancer]

I sailed 30,000 Miles with my shaft braked with a $20 vice grip.

[bradandnatalie]

Thanks for the reply. I just changed out my Maxi feathering props for fixed. The maxi props were worn and clunky and constantly needed cleaning to insure they opened fully. If I was racing I'd have them in a heart beat. on a cruising boat they are a massive pain in the bum. IMHO.

[bradandnatalie]

Thanks Uncle Bob that was a great article.

[FionaJC]

I let mine spin, in the drag vs noise debate I can live with noise. I have been tempted to rig an alternator to the spinning shaft but a. its too much hassle b. I think it would create issues under power. c. I dont care my boat iis a motor sailer so I get there quicker or enjoy the lack of engine noise so a spinning gearbox isnt an issue.

[Capn Jimbo]

Originally Posted by s/v Moondancer

I sailed 30,000 Miles with my shaft braked with a $20 vice grip.

This is without question, the most sensible and useful solution for the time being. Seriously. Unfortunately like the BMW cyclist in Zen and the Art of Motorcycle maintenance, fixing a problem with an aluminum shim from a beer can just was simply untihinkable by a certain number of owners.

I await the OP's solution...

[Frugal]

If the noise is limited to certain speeds you may have a resonance reaction on your shaft log seals.
Mt dry shaft log used to squeal between 3 to 3.5 knots. Quick fix was a drop of grease to "wet" the seal faces.

[jmschmidt]

Maybe you read the wrong test. A locked prop does not create more drag than a spinning one, not in a boat or in an airplane. A free-wheeling or wind-milling propeller will create drag equal to a solid disc the diameter of the prop. A locked fixed-blade prop will create drag slightly less that the surface area of the exposed blades. A folding or feathering prop on a boat will create the least drag.

If you really want to create drag, rig some kind of shaft driven generator, every KW of energy it produces is extracted directly from the power produced by your sails. There ain't no free lunch in physics.

Multi-engine propeller driven airplanes all have full feather propellers and many have auto-feathering systems which activate when an engine fails.