Drive train noises?

[Sinc]

Morning Everyone,
Over the weekend our boat developed some metallic rattlings from the drive.
This is a Westerly Fulmar with a Volvo 2002, shaft drive, ropecutter and 2 blade folding prop.
In reality there have prbably been rumblings for some time but it's now got worse and become metallic. Bad enough not to want to go far in her under engine.
Lots of investigation by myself and Seastart (very helpful) hasn't come up with any obvious cause.
Noise appears to be coming from underneath the boat. There's nothing obviously loose inside or out and the Seastart engineer pretty much excluded engine or gearbox problems. Video shows all the shaft, anode ropecutter etc in place and apparently OK. It's not precise enough to show vibration.
He did find a loose engine mount which may have put out the alignment but tightening and (roughly) realigning doesn't make the noise go away.
Three questions really
Any suggestions for the cause?
Any suggestions for further diagnostics before we have to lift her out?
Anyone recommend a good diagnostic engineer in or around Shamrock Quay?
Thanks in advance,
Graham

 

[Carduelis]

Rope cutter?

My first thought would be to check the rope cutter - they can come loose and rotate/ rattle around the shaft.

Can you disconnect the driveshaft from the gearbox easily? Then you can try running the engine gently in gear. If the noise persists it's engine/gearbox, not shaft.

 

[theoldsalt]

I had a similar noise on my boat. I eventually found that the shaft anode was loose .

 

[little_roundtop]

We have a similar rattle on our Yanmar shaft-drive. An engineer whose opinion I respect told me it was the damper disc, which is effectively the clutch plate (apparently). It's the disc in the front of the gearbox with four or five springs in it. Apparently the springs become loose in their mountings and rattle - that's the noise we can hear. He told me it'll be ok for another couple of seasons and then I'll have problems getting it into gear.

Perhaps that's your rattle too?

 

[Tranona]

Could be the well known spline wear problems in the drive plate with that engine/gearbox combination.

 

[Sinc]

We spent another few diagnostic hours today and came to the conclusion that the problem must lie under the boat in the P bracket area.
So we have arranged a lift out tomorrow and someone to look a tthe problem.
Many thanks for your suggestions.

 

[Leonidas]

We spent another few diagnostic hours today and came to the conclusion that the problem must lie under the boat in the P bracket area.
So we have arranged a lift out tomorrow and someone to look a tthe problem.
Many thanks for your suggestions.

I'm inclined towards Tranona's views, but once you have ascertained the problem, It will be interesting to hear the results of your investigation.

 

[Sinc]

Lifting her out showed the ropecutter to be the problem. It had somehow come loose and was gradually destroying itself! No idea why - been solid over two winter checks - maybe it had been doing its job and that had caused it to come loose - we'll never know.

Expensive aren't they!

Good thought Tranona but I forgot to mention the splines have been replaced with the upgrade.

 

[Carduelis]

Rope cutter

Yes I thought it might have been, having experienced the same problem myself recently. Depending on the make, you may be able to buy replacement parts. This is a bit cheaper than having to buy the whole thing which is, as you say, very expensive ...