engine mounts

[Guest]

It has been opined that I must grind out & remove the balsa core where my soon-to-be glassed in engine mounts will locate in my yacht hull. The motor is not excessively heavy - a 43HP Nanni, and given that the engine bearer grid will spread the load, and the great compressive strength of end grain balsa, would this be really necessary?
Any advice or opinions would be appreciated.

 

[jfkal]

Well I am not the expert. But Balsa does not sound strong to me. The weight might not be the problem but 43 HP is as lot of force to cope with. MY engine bed is glassed in hardwood and that is for a 27 HP engine.

 

[Strathglass]

It depends on the strength of the inner moulding. But I would think that if the new engine beds are made of adequate size to distribute the loads correctly then you would not have to break into the balse core. I would certainly refrain from breaking into the core if it was in any way possible, as ensuring the core was sealed adequately would be very difficult.
Perhaps laminating additional layers of GRP on the inner moulding with epoxy, prior to fitting the new engine beds would give the necessary strength.

 

[Plum]

I agree with Ian. Check the thickness of the inner moulding (do you have a core sample? If you need to drill a hole for the engine water intake through the hul near to the engine use a hole saw to get a core sample). If both inner and outer moulding are the same thickness then there is nothing to be gained by bonding the mounts to the outer moulding. Just make sure you have a good surface area, a well prepared roughened surface and use epoxy resin not polyester resin.

 

[PaulJ]

Balsa cored sandwiches are very strong provided the the skins stay laminated. I magine that the opinion you received would be based on the fact that the various forces concerned plus vibration could cause the sandwich to delaminate - then you would have a problem.

 

[Guest]

This sounds like a 'home-build' project with a new installation ????

If you grind out the core - you must make absolutely sure that all grain / cut faces are sealed well.

BUT what does the engine supplier recc'd ? What does a yard say ? In this case I would say forget the average amateur and average Yacht Surveyor ... this is a serious business and needs the right person to advise. 43HP may seem light and no problem to you, but that laminate / structure will carry various loads, vibrations etc. for years to come.
An example is my 32 HP lump .... now bedded onto angle iron with good Vetus mounts. The mounts are to solid timber bulkheads glassed into the hull which has no sandwich core. I am happy that this will survive till most around fall apart !

Honestly, I would advise that you seek prfessional advise ... we cannot see nor gauge your boat strength from a posting like this and you must be sure of the job done !