Prop shaft lock

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This topic contains 6 replies, has 3 voices, and was last updated by Voltair Voltair 3 months, 2 weeks ago.

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July 21, 2017 at 12:18 #26099
Czarina Blue
Czarina Blue
Participant

I’m finding that sailing along at 5 knots my prop shaft is turning merrily away. On other boats putting the stick into reverse gear ( with engine off) served as a prop shaft lock. But here it is making no difference.

Other jan rigging some restraining strap onto the shaft itself under the aft cabin floor’s bilge inspection board ( I see here is a tying off point provided there) is there any other way to restrain the shaft , learning wear?

Thanks

Duncan

July 22, 2017 at 11:46 #26100

Rhapsode
Participant

Hi Duncan, tying the shaft might mean losing time if you need the engine in a hurry. Have you been able to discover why the shaft still rotates when in reverse gear?

I sometimes put mine in reverse to stop the shaft rotating when I get tired of the noise. Often I find that it can be a struggle to get it out of reverse gear when I want it back in neutral.

Mostly I leave it to rotate. The shaft has been in position for many years and it doesn’t appear to have suffered any ill health from being left to rotate. I guess that there’s less drag from a turning prop.

Peter

July 24, 2017 at 15:46 #26102
Czarina Blue
Czarina Blue
Participant

Thanks Peter. So far I could only guess that it might be the reduction gear box that stops reverse engaging,or possibly that there is no oil pressure when the engine is off so that the clutch doesn’t allow engagement of gear? I’m not a mechano-technical person so really not sure, but thanks very much for your input.

Duncan

July 25, 2017 at 11:41 #26103
Czarina Blue
Czarina Blue
Participant

Thanks Peter. I guessed it could be the reduction gear box 2:1 that stops reverse engaging,possibly that there is no oil pressure when the engine is off so that the clutch doesn’t allow engagement of gear?

I have now read in the Perkins Marine Service handbook:

P65:
“On the Nicor TMP 12000 gearboxes it is necessary to run the engine after trailing the propeller for 12 hours to lubricate the gearbox.
…Transmissions operating reduction gear must have means of stopping the transmission output shaft from prolonged or continuous freewheeling. This is because the engine, being stopped, does not drive the oil pump in the gearbox. The box therefore is not being properly lubricated.”

So once again a case of RTFM !

But still thanks very much for your input. You may of course not have a reduction gearbox, but I know I do.

Thanks again

Duncan

July 25, 2017 at 13:05 #26104
Czarina Blue
Czarina Blue
Participant

This from Kevin O’Bryan of Thamesway Engineering today:
“The neutral brake only works when the engine is running.
The prop rotation when sailing will not damage the gearbox. If the noise is annoying you can lock the coupling as long as you remember to unlock it before starting the engine again.”

So take your pick, I guess!

My shaft is slightly loose so I’m keen to lose the rattling when under sail.

Cheers

July 26, 2017 at 14:05 #26105

Rhapsode
Participant

Glad you got to the bottom of it.

Good sailing.

Peter

August 29, 2017 at 08:06 #26149
Voltair
Voltair
Participant

On Voltair, we bought her with a shaft brake fitted already. But this was pretty weedy, and a real fiddle to engage and disengage, so we took it off. It also got in the way for accessing the sump.

Then we found that if you engaged gear (forward or reverse) BEFORE turning the engine off, it locked the shaft. In the book it says not to do this, because the engine restart can be hampered or prevented by the locking of the shaft. We never found a problem in practice, but if you got a rope around the prop and everything was tight, things might be very different.

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