Engine Mounting

[sapper]

Building a steel sloop and have been advised to bolt the inboard marine directly to the engine bearer rather than use "rubber" mounts. Am I right in thinking that vibration (if not noise) will be problematic ?

 

[stamfordian]

Hi,IMHOP,this seems to be commiting suicide,it will mean there will be no play or give and could lead to fractured castings ie bellhousing or block.Allthe noise would possibly resinate through the hull,would use anti-vibration mounts at least.
If you ding the prop on the bottom there would be no give throught he drive so somthing would have to give normally sheer pins etc but with no give at all the shock of this may crack the castings all my amature view of coarse..but we did once bolt an engine in a hotrod straight to the chasis ...this resulted in a broken bellhousing...typing crap tonight

[www.arweb.co.uk/argallery/stamfordian]

 

[seahorse]

Contact R&D Marine, they have a good website

Good advice & prices, i speak from experience.

 

[kgi]

seahorses post makes good sense, pyi is also good and if you can get hold of a vetus catalogue there is some useful info in there, personally i think a thrust bearing and quality engine mounts is the way to go........keith

 

[johnsomerhausen]

I have had two engines rigidly mounted on a 7 tons displacment steel boat I had from 1971 to 1987. The original was a 12 HP Arona which I replaced with a Yanmar 2QM15. I never noticed any special vibration and the noise did not prevent me or my crew from sleeping on a crossing from France to Brazil
john

 

[vyv_cox]

Modern thinking on engine installation has been to go the opposite way - mountings have become softer over the years and, coupled with flexible couplings and possibly constant velocity joints in the drive, this allows transmitted vibration to be kept to a minimum. I would be interested to hear why this advice was offered specifically for a steel hull, I can't see why the material makes any difference. I would almost expect the opposite - vibration transmission is far more efficient in steel than in wood or GRP.

Thinking about it from the opposite direction, why would flexible mountings be a problem? I can't think of any reason.

 

[ccscott49]

If you go with flexible mounts, you will need to go with a thrust bearing, in the drive line, to take the thrust of the prop, Halyard make one, nbut theye are not cheap, anti vibration mounts are just that, they allow a very, very small amount of give, and reduce the vibrations, but i see no reason not to bolt the engine directly to the beds, its been done for years, since steel boats and engines!

 

[dickh]

I agree with vyv cox, mount the engine on marine anti-vibration mounts(which are "fail safe"), a flexible coupling and a cv joint. See the Halyard Marine site or Vetus as suggested. I would be worried about bolting solidly down on to steel bearers, if there is any misalignment you could have problems.
However, the earlier post about the steel boat which had had two engines solidly mounting is interesting, the alignment must have been excellent - I suspect there was a flexible coupling in the drive line which accomodated small misalignments.
Go for the the AV mounts, flexible coupling and possibly a CV joint - its a well proven system.
Also fit leak free prop shaft seal - like the PSS seal.
For marine AV joints go to Trelleborg or Vetus.
good luck

dickh
I'd rather be sailing...

 

[chippie]

I agree with CCScott, solid mounting is fine if set up properly, and a hell of a lot cheaper than marine cv joints and the like.
I've been on quite a few boats with solid mounts and they have been no problem at all as long as they are done properly.

 

[bedouin]

In the world of steel narrowboats it used to be standard practice to mount the engine directly onto the steel bearers without any form of mounting. Provided that you get the shaft alignment right this does not cause any problems - noise and vibration are not a significant problem because the engine is rigidly coupled to a massive structure - in general the bigger the bearers the less the vibration.

More recently there has been a move to flexible mounting systems - with flexible engine mounts and couplings. In my experience these do tend to have less vibration, though not massively so, but no significant change in the noise.