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Prop loose on shaft?

Beneteau381

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Engine is very poorly and out of the boat.

Cleaning out the empty space today I casually twirled the coupling. Seems like there is a couple of degrees play in both directions before the prop turns.

Is the prop loose on the shaft, and if so why? Don't want to add a Cascais liftout to the cost of fixing the engine. (Plan is to have a wee sail around the Algarve then lift out at Bruce's if there is space, so will fix wonky props etc then, but will it fall off before then?)

- W
A lot of suggestions. Get the evidence, is the shaft all one piece to the prop? Is the coupling flange you twiddled tight to the shaft? Do you have a rope cutter, one of those guillotine ones, not a circular one? If your prop had been loose I would not have expected it to stay on or drive for long, If it was loose it would have been driving on the key alone and and I would have expected it to have sheared by now.
 

webcraft

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Looks like it might be time to go marina snorkeling again...

(Last time was for a lost hearing aid in Nazaré...)

- W
 

webcraft

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Why out of the boat? Last I heard it was most likely just a head gasket problem.
My engineer disagreed. I don't know enough and I trust him, so out it came. Good opportunity to get all the oil out of the bilges.

Don't have a rope cutter, and as far as I can remember there is no anode either because there wasn't room, although it was over a year ago and I am not sure.

Here's a pic of the prop a day or so before launch, which was August last year









- W
 

Beneteau381

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My engineer disagreed. I don't know enough and I trust him, so out it came. Good opportunity to get all the oil out of the bilges.

Don't have a rope cutter, and as far as I can remember there is no anode either because there wasn't room, although it was over a year ago and I am not sure.

Here's a pic of the prop a day or so before launch, which was August last year



Looks solid enough, I doubt it is loose, as I said, if it had been loose it would have become a lot looser very quickly. Maybe some debris in the aperture catching the prop?





- W
 

Rappey

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2 nuts and no split pin ? would that mean the prop is not suitably mated to the shaft ? does the taper in the prop match the shaft taper?
Is it possible the nuts are still locked together but not tight against the propellor..
 

RichardS

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2 nuts and no split pin ? would that mean the prop is not suitably mated to the shaft ? does the taper in the prop match the shaft taper?
Is it possible the nuts are still locked together but not tight against the propellor..
It is possible to tighten up two locknuts and, in the process, inadvertently relieve the pressure on the fitting that you are trying to secure. I've done exactly that on an number of occasions over the years although I've always realised what has happened and corrected the problem. It's not a fool-proof system.

Richard
 

webcraft

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It is possible to tighten up two locknuts and, in the process, inadvertently relieve the pressure on the fitting that you are trying to secure. I've done exactly that on an number of occasions over the years although I've always realised what has happened and corrected the problem. It's not a fool-proof system.

Richard
I have no idea. The engine has however run for at least 150 hours without the prop falling off.

- W
 

webcraft

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2 nuts and no split pin ? would that mean the prop is not suitably mated to the shaft ? does the taper in the prop match the shaft taper?
Is it possible the nuts are still locked together but not tight against the propellor..
All quite possible. The 'brilliant marine engineer' who set it all up has been revealed as a serial bodger, so anything is possible.

I do not understand why the shaft would turn slightly in either direction before engaging the prop. Surely the key is either engaged or not - or is the key itself tapered? If there is no key and it is just a tapered fit on the shaft and has slid down, then I don't see how turning it would give positive engagement reliably in either direction.

I am probably not explaining this very well, but I think an underwater inspection is required. It is getting chilly here though and I am not keen...

- W
 
Last edited:

bikedaft

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All quite possible. The 'brilliant marine engineer' who set it all up has been revealed as a serial bodger, so anything is possible.

I think an underwater inspection is required, but it is getting chilly here and I am not keen...

- W
Where are you? (I like swimming!)
 

Rappey

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I do not understand why the shaft would turn slightly in either direction before engaging the prop
if there is slight movement in the prop it can keep hitting against the key and it will slowly beat it down until the prop freely spins on the shaft..
If you can turn the shaft inside and feel it clunking elsewhere I would guess the prop is quite loose.
 

RichardS

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I have no idea. The engine has however run for at least 150 hours without the prop falling off.

- W
That would not, in itself, be surprising as the locknuts might well be properly locked together so the prop will never fall off ...... but, if the prop is tapered and keyed, or just uses a tapered key, it might clunk from side to side.

Richard
 

webcraft

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That would not, in itself, be surprising as the locknuts might well be properly locked together so the prop will never fall off ...... but, if the prop is tapered and keyed, or just uses a tapered key, it might clunk from side to side.

Richard
If the nuts have not moved and the prop was tight on the shaft before, what can have moved or worn to cause this?


- W
 

bikedaft

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Ooh, i would love to swim there. Pay flights from Glasgow? 😉

There must be someone nearer you who would do it for fun or a pint?
 

bikedaft

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If the nuts have not moved and the prop was tight on the shaft before, what can have moved or worn to cause this?


- W
We had 2 nuts, but the woodruff key sheared along its length, so prop was captive, but useless. A lot of breath holding later, and two shifters, fixed it enough to last the season (prop off, new key on, prop back on)
 

Beneteau381

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We had 2 nuts, but the woodruff key sheared along its length, so prop was captive, but useless. A lot of breath holding later, and two shifters, fixed it enough to last the season (prop off, new key on, prop back on)
Thats mypoint, if the prop was loose then the key would have sheared and no drive
 

greeny

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In a fraction of the time its taken to debate this on here, someone could have been in the water and checked it out. Water cold, no wetsuit onboard, Decathlon. You may need a rope round keel to pull yourself down. 2 minutes in the water and all will be revealed. Then you can debate the solutions.
 
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