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Old 13-11-2014, 17:27   #16
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Re: Locking the prop's shaft -- damage?

Isn't there a commercial shaft lock or brake available to lock the prop shaft? Something similar to a disk brake on a car?
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Old 13-11-2014, 17:39   #17
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Re: Locking the prop's shaft -- damage?

I have a 3gm30f with a fixed 3-blade prop and just had my tranny rebuilt last week due to the gears wearing down from years of locking the prop in gear under sail (as per mechanic here and the tranny shop). You could put the tranny in forward gear and give the shaft almost a full turn before it locked in.

I believe Yanmar actually sent out a service bulletin on this topic in recent years.
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Old 13-11-2014, 18:42   #18
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Re: Locking the prop's shaft -- damage?

Quote:
Originally Posted by laika View Post
I have a 3gm30f with a fixed 3-blade prop and just had my tranny rebuilt last week due to the gears wearing down from years of locking the prop in gear under sail (as per mechanic here and the tranny shop). You could put the tranny in forward gear and give the shaft almost a full turn before it locked in.

I believe Yanmar actually sent out a service bulletin on this topic in recent years.

Here is the Yanmar MSA:

Yanmar Gear Position While Sailing




.
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Old 13-11-2014, 18:57   #19
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Re: Locking the prop's shaft -- damage?

Last March I took a diesel engine course organized by the national womans sailing association. The instructor, John Farrell from Mack
Boring said Yanmar engines should be left in neutral. Not in reverse. it is stated as such in the engine manual. I guess a lot of us were taught to put the engine in reverse to prevent the free wheeling.
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Old 13-11-2014, 19:42   #20
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Re: Locking the prop's shaft -- damage?

I believe the original reason to prevent freewheeling by putting your engine in reverse was that some transmissions did not circulate trans fluid/oil if the engine was not running. Not to mention that it was noisier.

Yanmar now posits that having the trans in reverse under sail can damage the trans (see one of the earlier posts).

There has been an ongoing argument as to whether freewheeling creates more or less drag than being locked in reverse. A couple of years ago I read an article by a scientific type that said that freewheeling produced less drag. I didn't understand all of what he said, but it sounded logical, and he had a whole bunch of capital letters after his name so he convinced me.

Not to mention that I have Yanmars so the factory convinced me also.
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Old 13-11-2014, 21:22   #21
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Re: Locking the prop's shaft -- damage?

As with FSMike, I also read a very scientific type article - there was an argument on this subject at my sailing club and since there are Boeing engineers everywhere someone researched it. The conclusion is that people are taught to put the engine in reverse to stop the spinning b/c the noise bugs the crap out of people. There should be less drag if it is spinning. But it seems drag isn't the only issue (unless you are a Boeing engineer).

My Perkins 4-108 spins no matter what while under sail - forward, reverse, neutral - doesn't matter if I am sailing fast enough. However, I haven't yet tried switching to reverse when I hear it stop after I slow down...I will try this. According to my crusty 40+ year old Perkins manual it depends on the type of gearbox with some being fine to freewheel for 12 hours before needing to run the engine to lubricate the gearbox, some ok up to 8 as long as shaft speed doesn't exceed certain limits, and some (reduction gear) needs to be stopped to prevent continuous freewheeling b/c the engine isn't driving the oil pump in the gearbox, and some can be trailed for any length of time provided your gearbox oil is full. My Challenger 32 manual says I need to run the engine for 15 minutes every 6 hours I'm under sail alone.
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Old 14-11-2014, 09:01   #22
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Re: Locking the prop's shaft -- damage?

It's only logical that a freewheeling prop would produce lees drag but if it harms the transmission or drippless shaft seal, you really should follow the manufacturer's recommendations.

So is there a commercial shaft lock available or is a pipe wrench the only choice?
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Old 14-11-2014, 10:12   #23
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Re: Locking the prop's shaft -- damage?

per the Perkins manual "Propeller shaft brakes ae available and the boat builder or stern gear specialist should be contacted for further details.
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Old 14-11-2014, 21:07   #24
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Re: Locking the prop's shaft -- damage?

I have a Yanmar3GM30 and at some time in the past became aware of the recommendation that Mainesail posted so I usually leave it in neutral. But it's pretty noisy. I'm wondering if I should come up with some kind of brake for the shaft. I'm sure I can engineer something. It would also make me feel a little better about wear and tear on my dripless shaft seal. Somehow, having the shaft turning all of the time seems like it will shorten the lifetime of the seal.

I wonder if there is a consensus on making some kind of shaft brake??

Bill
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Old 15-11-2014, 07:27   #25
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Re: Locking the prop's shaft -- damage?

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Originally Posted by Bill_E View Post
I have a Yanmar3GM30 and at some time in the past became aware of the recommendation that Mainesail posted so I usually leave it in neutral. But it's pretty noisy. I'm wondering if I should come up with some kind of brake for the shaft. I'm sure I can engineer something. It would also make me feel a little better about wear and tear on my dripless shaft seal. Somehow, having the shaft turning all of the time seems like it will shorten the lifetime of the seal.

I wonder if there is a consensus on making some kind of shaft brake??

Bill
I have a dripless shaft seal and as I recall, the shaft must be secured against turning if the boat is being towed, Is a trawler, not a sailboat so that's the only time I would be moving without the engine running and supplying water to the shaft seal.

If you come up with anything I would like to see it. Preferably something that doesn't require disconnecting the shaft.
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