Verified answer

use a board type fireproof material. they make a special type fiberglass for engine compartments. attach to the engine hatch with mastic. local boat dealers should have it.

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RE:

What is the best material to insulate an engine compartment in a 40' boat? Yanmar 6YL2A 440hp x 2

There is not much room above the engines (less than 1 foot) the seats for driver and pax are directly over the front of both engines. The boat is great but it is loud. What is the best method to quiet the noise?

Engine Compartment Insulation

Been there & done that...

I forget what it is called, but, there is a Marine (USCG approved) Acoustic Vinyl/Foam & Lead sound Insulation Headliner (padding) made specifically for Marine engines and generator compartments. The are specifically designed for "sound suppression".

I had this problem a few years ago (I really like my vessel to be "NICE & QUITE" and this "soundproofing insulation" was recommended to me... as I recall, it wasn't cheap - but, not a lot is needed. So, I bit the bullet and bought it, took it to the boat and installed it on the underside of my hatch (access) covers. Never was so pleased with an aftermarket boat product,,, the stuff really did the job - kept the engine and vibration noise from being noticeable at all - unless you specifically listened for it.

Happy & Safe boating!

PS. Your in luck, I found it on the link below.

http://www.cyber-bridge-marine.com/coast-guard-app...

There are choices to make that only you can make on this one as you know your boat better than anyone who signs in here.

Check out the link below from Nautic Expo, a web site that features items you can buy. There are several choices to abate the noise level from panels to a spray on foam. Also note to that a Google search turned up many vendors selling these items so you may find it cheaper elsewhere.

Good luck!

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A person who does things the way it is supposed to be done in their marriage life. Etc. Full fill the family need to, be the leader of the house. Etc.

The rubber foam works but falls apart> Lumber yard 3/4" foam aluminumm both sides caugh or screw with washers>Have done many this way>