engine compartment sound insulation

[George DuBose]

I am looking for the best rated sound absorbing insulation for my engine compartment. The engine is not in a small box or room, rather under the cockpit and hence open to all of the aft storage areas.

I would like to find a product that absorbs the sound, is fireproof and self-adhesive.

Thanks.

George

[tkeithlu]

Let's think about the task first. You need to keep all the auditory frequency vibrations inside the engine compartment, and then dampen them in the insulating material. You're behind the eight ball from the beginning, because your engine compartment is open to the stern. Designing a tight box while not denying your engine cooling and breathing air is the first step. Apply insulation on the inside, and include the tube that lets air in. Leave absolutely no cracks or gaps. Given a fiberglass hull, you may need to go under the engine as well.

Most of the insulating boards or rolls for this job are laminates of foam and a material that just does not transfer vibrations. Some use plastic layers, but from a potential efficiency perspective I suggest lead foil. Here are Defender's offerings:

https://www.defender.com/category.js...05&path=-1|311

There is a secondary problem with vibrations outside the auditory range (50-20K Hz) setting up vibrations in other bodies, such as fuel tanks, that are auditory. You really do have to keep all that stuff inside your box.

What's best? I don't know. we might have a provider with experience comparing types. I'm inclined to believe perfection in sealing is more important than your choice of material.

Here's what Yachting Monthly said about it, which is pretty much what I just said:

Guidelines on installing marine engine soundproofing:
Foil/cloth and hard barrier soundproofing is best cut with a sharp modelling knife – but it’s easier and neater to cut the foam using
a serrated blade. Thinner sheets cut well with good scissors.

Self-adhesive sheets are easy to peel
and attach, but you must position it correctly first time. Plain-backed types
require spray or brushed contact adhesives – the latter being more controllable
in tight spaces. Mechanical fixings should be added to all horizontal upper
surfaces.

Suppliers advise that all joints are covered
using special joining tape to avoid ‘leakage’. Self-adhesive foil tape
works excellently on foil-covered material, but white plastic tape
from Vetus will peeled off easily.

Ideally, soundproofed bulkheads should
totally encase the engine area, separate from any tanks, which can resonate -
amplifying the sound. Engine noise can ‘flow’ along the bilges, so where
possible bulkheads should continue down to the hull, leaving only limber holes
for bilge water.

Remember to provide enough airflow for
combustion. Open air holes will ruin the insulation, but a simple baffle will stop most of the noise escaping.

Finally, all cables and pipes should pass
through snug-fitting rubber grommets, while any covers or side panels should
fit snugly with a noise-tight seal.

[Wood]

High frequency sounds will be attenuated with rock wool [fireproof] or similar. Low frequency attenuated by mass loaded vinyl. Not fireproof but has a zero flame spread rating.

[Emmalina]

Use car insulation self adhesive and cheap !https://www.lazada.co.th/products/no...kms9Z&search=1