Insulating noise

[Bunbury]

I have an old 2 cyl 17 hp Arona diesel in my yacht. Its very noisy in the cabin as it thumps away. Is there anyone out there who knows what I can use to insulate the box cheaply and efficently. Or is spending big money on sound proofing the only way. one person suggested cork? will this work or will it rot. The boat is carvel planked. The engine box is ply wood.

[gwilli]

Noise isolation is tricky. The first check is to make sure your mounts are still resilient and not dried and hard. Make sure there are no short circuits around them for vibration from the engine to transmit to the hull or engine enclosure (directly touching). Low frequency because of long wave length is difficult to isolate as it travels through barriers but closed cell foam or preferably closed cell foam with lead-vinyl backing will provide some high frequency absorption. Same kind of stuff is used for machine enclosures. Closed cell is necessary so it doesn''t get saturated with oil. Also very important to ensure a tight fit of enclosure adjoining inhabited spaces. A tiny crack can let through a lot of noise. Of course you need air for the diesel but this should come from spaces indirectly adjoining or baffled from liveable areas. Good luck.