Prop shaft coupling fails when going hard astern

[pvb]

Well, that's all right then if the OP said it, I mean it must have been torqued correctly, mustn't it?

Hmmm...

 

[charles_reed]

Ooh, I shall speak to the skipper when I get home tonight - he's a computer/forum phobe and won't be watching this thread himself. But as mere crew I have to say I didn't spot any prior warning signs. Could you elaborate?

It's a brand new propshaft and brand new coupling - well new with maybe 2 hours of motoring on it.

We did indeed 'gun it in reverse' but the coupling should surely withstand that? There was no evidence that the prop has bent, but we lift out for the winter mid October and won't be using the boat before that so we'll have a good look over the winter.

In the meantime Paul will be speaking to Vetus and the engineer today. Will keep you posted.

I shall be posting another thread thanking Gosport (Premier) marina staff as we were very impressed with the serivice and help we received.

thanks

Sharon

There is plenty of warning - engine occasionally racing and a squealing sound from the clamp - once it's happened to you you'll know the signs.

 

[Poignard]

There is plenty of warning - engine occasionally racing and a squealing sound from the clamp - once it's happened to you you'll know the signs.

I have installed a Slip Detection Device on my Centaflex coupling.

A blob of paint on the coupling, directly opposite a similar one on the shaft. Every now and then I check they are still in line.

 

[Windfall]

There is plenty of warning - engine occasionally racing and a squealing sound from the clamp - once it's happened to you you'll know the signs.

Yes but there wasn't any of that, one minute we had drive, the next there was a loud bang (probably the prop hitting the rudder - which now has a tell tale gouge) and no drive. Really no warning over the preceding hours of use either.

& of course you only have my say so that it was installed correctly, but what advantage in lying? We're only trying to work out what might have happened in the hope that we can prevent it happening again.

 

[pvb]

& of course you only have my say so that it was installed correctly,

Who installed it? And did they use a torque wrench?

 

[Windfall]

Who installed it? And did they use a torque wrench?

OH installed it and yes he used a torque wrench and installed it under the guidance of a Vetus fitter. Said fitter is not contactable during the day at the moment but Paul will speak with him this evening.

 

[Tranona]

Not sure the torque is that critical. I have had a Bullflex for years and only ever tightened it with a normal Allen key. That gets it plenty tight as it is always hard to get undone and has never slipped. I would get a micrometer on your new shaft as it could be metric - that is 25mm against 25.4mm for an imperial shaft.

 

[pvb]

Not sure the torque is that critical.

The installation instructions (always worth following) specify putting grease under the heads of the clamping bolts and then torquing them to certain minimum levels, which vary according to the size of the Bullflex.

 

[NealB]

OH installed it and yes he used a torque wrench and installed it under the guidance of a Vetus fitter. Said fitter is not contactable during the day at the moment but Paul will speak with him this evening.

Might be worth knowing that Windfall's other half is a time served, apprenticed, experienced, tool maker.

 

[pvb]

Might be worth knowing that Windfall's other half is a time served, apprenticed, experienced, tool maker.

Professionals are notorious for not reading instructions!

Obviously I'm not suggesting that Mr Windfall ignored the Bullflex instructions.

 

[2copplane]

I had a similar lost drive on a penta2003 with a six bolt clamp. I'd literally just checked the clamp bolts were (very) tight following a relaunch, after reversing out gave her full throttle and..nothing. While drifting around the marina basin I nipped below and found the shaft could now spin freely in the coupling.

After tying alongside another boat I nipped down and tightened them all up again and was fine ever since. A spec of rust/muck must have been on the shaft when I fitted it and the full revs broken it up and allowed it to spin freely.

It looks like yours was a new shaft an clamp so perhaps may have just been a burr, rather than rust.

 

[Norman_E]

Cannot help with the problem, when it happened to me on my last boat the last owner had put a jubilee clip round the shaft "just in case" :/

As some one suggested here I know keep my "spare" shaft anode stored on the shaft between the engine and stern gland "just incase":/

I too use an anode because on my boat the rudder is far enough away to allow the whole thing to fall out. I suggest not using hose clamps as they are likely to wreck a Volvo type shaft seal if they hit it with the prop still turning the shaft, whereas an anode will probably not do any damage.