Drive vibrations - Help!

[Pelican]

I have a 32 year old Benateau motor sailor fitted with the original Volvo Penta MD2B. I have owned this boat for twelve years and during this time the engine has been rebuilt twice. I use the boat all year around and live on board in summer. During the last four weeks I had the boat refitted, the most important job was fitting new engine bearers - made of stainless steel, bolted and glassed onto the old engine bearers, rewiring, new batteries etc. On making trials yesterday the engine ran very smoothly at low and almost full speed (I don't have a rev counter - play it by ear!), BUT at mid range speeds there was an awful lot of vibration from the engine. It has always done this but it was more severe yesterday perhaps because the engine is now properly attached to the boat - a few years ago the engine mounts broke and the engine was just sitting on the bearers - and I used it this way for one year without been aware of the problem...

My question is - does there exist some sort of rubber fitting that I could fit between the gearbox and the drive shaft to stop/lessen the vibrations? The drive shaft is straight and there is no damage to the prob.

Any suggestions/advice gratefully received!

Thank you very much and happy boating!

Pelican

 

[vyv_cox]

I assume from your post that there is currently no flexible coupling at all? There is a whole range of options available, at a range of costs, I suggest that a convenient way to overview them all is to look at a Vetus catalogue. There is a description of them all that you will find helpful. The final and most expensive option is an Aquadrive, marketed in UK by Halyard.

Before installing some new kit in a setup that has operated well for 32 years, I would try to find what is causing the problem. It sounds to me that you may have some "soft foot", i.e. one or two mounts are not fully loaded. Also check the shaft run-out, it should have very little, maximum about .010 inch. The vibration may be combustion-induced, have you checked injector spray patterns?

 

[AndrewB]

Alignment problems?

Very often the cause of new vibration. Obviously you will have aligned when the engine was replaced. Was it done before relaunching, as the yacht may take a different shape in the water? Might be worth checking again.

 

[rogerm]

Re: Alignment problems?

I don't have that sort of system so this is just a suggestion..... Since it only happens at mid-revs perhaps the inherent vibration from the engine is setting up a sympathic vibration in something nearby ie perhaps, say, the battery is leaping up and down....?
Roger

 

[richardandtracy]

Could well be misalignment etc, but I would also suggest that it's worth considering using Anti-Vibration mounts under the feet of the engine. You never see a car without them.... and they do absorb the energy of forced vibration before large amplitudes can build up.

Final thing - are the bolts at the feet all tight now? Could be from the engine tapping a different foot from when the bearer was broken.

Regards

Richard

 

[byron]

I hesitate to say this because of what a fix would cost. Check the Gearbox it could be that though I sincerely hope not. But!! the symptoms you describe match my problems last year and that turned out to be the problem, the thrust bearing on the gearbox had gone.

http://www.alexander-advertising.co.uk

 

[yoda]

Given the major change you have made is to the alignment I would in the first instance recheck it. Sometimes the misalignment which is most noticable at medium speed can appear negligable at high speed but still be there. remember that getting the alignment right if you have no flexible coupling is very important and worth getting right and that it needs to be done in all planes.

Yoda

 

[seahorse]

Re: Drive vibrations - R&D MARINE!!

I binned my MD2 & fitted a Kubota, they were very helpful, prices were low & delivery was quick.
Catalog is available at their web site.

Highly reccomended.

 

[Pelican]

Thank you gentlemen for your helpful suggestions and thoughts - I will check these out over the next few days and keep you posted on findings/solution!

Best wishes

Pelican

 

[Trevor_swfyc]

If the engine mounts broke and you used the boat for two years then you would have worn the cutlass bearing oval and this could cause vibration, resonance in the shaft.
Worth considering.
Trevor.

 

[Pelican]

Vibrations update (and a bit of waffle!) - Yesterday the weather here in Geneva was lovely not a cloud in the sky, a warm breeze (well 12 degrees) the new snow glistening on the mountains and so at about 3pm, got the nautical urge and so I left office jumped in car and 10 minutes later am at the harbour - hop in tender - a Pioneer Maxi with 5hp Honda and out to boat which is on a swinging moorings. Start engine, cast off and head for Geneva 7 or so kms away - put on autohelm - go below light Bengco (for return journey) fix a drink - stroll around deck - not a ripple on the water and only two other boats in sight. Go at 80% speed to avoid vibrations. Half an hour later arrive in down town Geneva and tie up at boat yard.

Update - have ordered a Vetus flexible coupling - but unfortunately it will take two weeks to be delivered from The Netherlands - no stocks in Switzerland.

Have a drink or ten on board with engineer and crew. Now its dark and cold (about 5-8 degrees) so retire below (where Bengo has warmed up cabin nicely to about 20 degrees) and with not a sausage in sight (at least with lights on) plow
back up the lake. Vibrations - whot vibrations! I have a Astrodom fitted on the hatch and a remote for the Autohelm so no need to go on deck til harbour looms up. Tie up boat, fall in dinghy, fall in car which takes me home in 15 minutes! Today its pissing down and back to reality!
Cheers

Pelican