Prop shaft rattle/knocking sound

[Sinbad1951]

Agree with Charles Reed above totally. I would suggest one of two causes if the shaft isnt hitting the stern tube. 1. Bearings in Stripper rope cutter need replacing, or 2. If the prop has its own anode attached there is a possibility that wear/corrosion on the anode and its attachment fixings has effectively unbalanced it. I suffered from this and it was only apparent whilst the boat was moving forward. Water pressure effectively pushing one side of the slightly worn anode off centre.

 

[Carduelis]

Agree with Charles Reed above totally. I would suggest one of two causes if the shaft isnt hitting the stern tube. 1. Bearings in Stripper rope cutter need replacing, or 2. If the prop has its own anode attached there is a possibility that wear/corrosion on the anode and its attachment fixings has effectively unbalanced it. I suffered from this and it was only apparent whilst the boat was moving forward. Water pressure effectively pushing one side of the slightly worn anode off centre.

I'm fairly sure that the shaft IS hitting the stern tube, mainly because of the 'tone' and location of the knock. I've experienced a loose Stripper (!) Before and the sound was more of a rattle.

I think the 'loose cable' theory unlikely too. Partly for a similar reason and partly because there isn't anything much in the vicinity of the tube.

The thing that foxes me most is that the noise is loudest at low revs in-gear while the engine is cool. It goes away somewhat after it warms up - although not entirely.

So; my thinking at the moment is that the engine mountings need adjustment. Engines do vibrate a bit more when cold. OR the whole problem was caused by the pretty excessive prop fouling and possibly a reduced flow of water through the cutlass bearing because the intake was fouled.

I'd be grateful for any comments on the above.

For those who wanted more details of the setup: the engine is a VP2040. Volvo gearbox and shaft seal. The shaft runs in a keel log to an all rubber cutlass bearing. There is a rope cutter and three bladed fixed prop with anode.

Thanks again everyone for your help.

 

[cmedsailor]

For those who wanted more details of the setup: the engine is a VP2040. Volvo gearbox and shaft seal. The shaft runs in a keel log to an all rubber cutlass bearing. There is a rope cutter and three bladed fixed prop with anode.

Thanks again everyone for your help.

Just curious, is it a Beneteau Oceanis 361 with a VP2040 instead of the usual VP2030?

 

[Carduelis]

Just curious, is it a Beneteau Oceanis 361 with a VP2040 instead of the usual VP2030?

Its a Beneteau Oceanis 36 CC.

 

[Spyro]

I'm fairly sure that the shaft IS hitting the stern tube, mainly because of the 'tone' and location of the knock. I've experienced a loose Stripper (!) Before and the sound was more of a rattle.

I think the 'loose cable' theory unlikely too. Partly for a similar reason and partly because there isn't anything much in the vicinity of the tube.

The thing that foxes me most is that the noise is loudest at low revs in-gear while the engine is cool. It goes away somewhat after it warms up - although not entirely.

So; my thinking at the moment is that the engine mountings need adjustment. Engines do vibrate a bit more when cold. OR the whole problem was caused by the pretty excessive prop fouling and possibly a reduced flow of water through the cutlass bearing because the intake was fouled.

I'd be grateful for any comments on the above.

For those who wanted more details of the setup: the engine is a VP2040. Volvo gearbox and shaft seal. The shaft runs in a keel log to an all rubber cutlass bearing. There is a rope cutter and three bladed fixed prop with anode.

Thanks again everyone for your help.

In that case I'd go with disconnecting the coupling like Tranona suggested. The Volvo seal should self centre so you will be able to tell if the engine needs to be moved to line up with the Coupling. You mave have some droop due to the weight of the coupling be aware of that. That can all be done without an expensive haul out.

 

[cmedsailor]

In that case I'd go with disconnecting the coupling like Tranona suggested. The Volvo seal should self centre so you will be able to tell if the engine needs to be moved to line up with the Coupling. You mave have some droop due to the weight of the coupling be aware of that. That can all be done without an expensive haul out.

Yes, agree, it can be done. This is how the alignment on my Ben361 was made. The distance between Volvo seal and cutlass bearing cover probably the 2/3 of the shaft and therefore self centre it. But the cutlass bearing need to be new (good condition in other words).

 

[Robin]

Its a Beneteau Oceanis 36 CC.

The same boat as we have now except we have the Yanmar 3GM30. We had a new Racor filter setup installed in ours as the original (Benny France) fitted filter of unknown make was impossible to get at to service especially in a hurry, and after that if the engine hadn't been run for a week or two it would start up very lumpy and shaking really badly, (probably the high output 150A alternator load cutting in didn't help). Our engineer checked it all and said the fuel was draining back to the tank which is low down and the engine lift pump is a fairly puny one. he said the in- built non-return valve in the new Racor filter was probably stickingand fuel drained back to the tank ( they do that sometimes he said ). He said to keep the fuel tank topped up and run the engine a bit every week if we could in the off season if we were not using the boat regularly. We do that (usually run it for 5 or10 minutes in gear in the berth) and have had no more problems since then. we have a 'Volvo' seal too, a new one fitted when we last lifted out and our shaft might have been banging in the tube as others have suggested, possibly the standard Benny 36CC engine mounts are quite soft and allow more movement than is ideal.

 

[Spyro]

Another thought. Could the bigger 40hp have a larger diameter shaft making the clearance in the shaft log rather small?

 

[Robin]

Another thought. Could the bigger 40hp have a larger diameter shaft making the clearance in the shaft log rather small?

You may be right, ours was larger than expected and we had to order a larger size Volvo seal as the one first supplied via Benny USA was too small, At the time I thought this was a simple confusion between USA built Bennies and French built ones as our is., but maybe at some stage they 'rationalised' and fitted a larger shaft on all versions.

Added PS I just checked and our shaft is supposedly 30mm according to the purchase surveyor man but he thought it was 1.25" initially, I didn't personally measure it and yanks don't understand metric.

 

[Carduelis]

Just to report back on this for the possible benefit of others; I finally got an Engineer to look at the problem this week. He removed the Volvo seal and found that the shaft was low in the tube. The engine mounts have very little adjustment on them so he recommends changing them all. He will also be replacing the shaft seal and cutlass bearing so it looks like I'm in for a big bill...

Anyone know a source of aftermarket/discounted engine bearings BTW. The VP ones are £120 each (x4)!

 

[Spyro]

I'd recommend another engineer. He should be able to tell you what other mounts are available. You could put shims under the mounts?
I take it you mean mounts rather than bearings?

 

[Tranona]

Try Vetus, Robush www.robush.co.uk or R&D for mounts.

 

[Carduelis]

I take it you me mounts rather than bearings?

Yes I mean the rubber/metal engine mountings. There are two under the engine and two at the gearbox end.

I'm mulling over doing it myself, but it's a bit fundamental and c*cking it up could be even more expensive. I don't fancy a loose engine in a rough sea either!

Getting the alignment right afterwards also sounds like it might be tricky to do well.

Thanks for the supplier suggestions.

 

[GrahamM376]

It's not a good idea to have the mounts right at the top of the adjustment range but, if they're in good nick, instead of replacing them (as Spyro says) inserting spacer blocks is normal practice and cheaper than new mounts, mine were milled by local engineering shop out of scrap material and cost around 25 euro.

All the work you mention can be DIY and there are usually enough people around a yard to advise or help if you get stuck, aligning an engine isn't difficult. Good learning exercise.

 

[Modulation]

+1