fitting the floors that support engine foundation

i will put the floor timbers that the foundation of the engine(the frame that engine sits on) is attached by screws.
should i use epoxy of polyurethane sealant to attach the floor timbers to the hull and keel?
i was thinking polyurethane sealant is better for damping the vibration and i am afraid that epoxy can crack by vibration of the engine

regards
Ulas

 

I would check with Sikaflex, they have products that do just that, bond tenaciously while deadening vibrations.
High Strength Bonding 01a402sa05 https://usa.sika.com/industry/en/industry-markets/marine/Cruise_Ships_Ferry_Boats/01a402/01a402sa05.html

Another good one is Plexus but they are pricey!

 

I am in Tunisia and i don't have many choice. I found a mastic here called "pattex" which can be used on the roof. Doesnt a normal polyurrthane mastic do the job? It is a 31 feet boat.

 

I wouldn't use a product to connect my motor to the hull and keel if it's only labeled as a SEALANT. You need an adhesive. We use polyurethane mastics to repair concrete and stucco maybe they also make adhesives, I don't know. Think you would be better off glassing it before using a sealant.

 

Secure floors and long girders to the hull as best as possible (jorgepease recommendations) and, if you have vibration problems, use silentblocks or something similar between the engine and the bench. It is necessary to avoid, as far as possible, that the vibrations reach the hull or its reinforcements.

 

There are three separate concerns to approuch here: longitudinal engine bearers, the mounts and dampeners. The engine bearers are the structural elements, usually given enough with to set the engine on mounts within a range you don't have to go nuts with weird shaped mounts, just to make them work. The dampeners often have a mount built into its base, but most commonly they aren't of sufficient area to adequately support the weights involved. For example, a small block Chevy with the obligatory Velvet drive attached is easily 1,000 pounds of hardware. The dampeners usually have a few square inches of contact surface area to support this, which is woefully inadequate for 1/2 a ton of loading, even with bonded fastener holes.

Ideally these three elements are treated desperately on wooden boats. You're married to the engine bearers, so the mounts and dampeners are where the cleverness needs to occur. For the mounts, a fairly heavy plate or maybe a wide hunk of angle stock is placed on top of the bearers and the dampeners are attached to these. This dramatically increases the contact patch on the bearers and also offers some additional adjustments for alignment.