Engine Room Sound Insulation

This page was last updated on 15 January 2002

Well, I had the insulation in hand before the boat went in the water last spring, but just couldn't find the time to get it installed at that point.  Then, I didn't want to take time away from sailing and more critical projects during the summer of 2001.  Finally, the time has come to install my sound insulation in the engine room!

I purchased some high quality (read: expensive!) 1" foam/lead insulation from Hamilton Marine.  This is manufactured by Sounddown and features 1/2" of acoustic foam on each side of a lead core, with a foil/Mylar facing on one side.  This is the good stuff; the products without lead just aren't as effective for a given thickness.  It weighs 1 pound per square foot.

Of course, the engine room itself is now full of stuff that is attached to the side walls--fuel filters, electrical equipment, etc.   This will make installation of the insulation more difficult, and I haven't decided how to proceed yet.  However, I did remove several pieces of my engine box that are readily transportable, and brought them to my shop to take care of the insulation on those parts.

A short time ago, I was digging around in my storage room for something and moved the box that the insulation was stored in--it's a 4x8 sheet, rolled up.  Well, I got hit directly in the face above my eye by a very surprised squirrel who had taken up residence there!  Therefore, I was hardly surprised when, a week or so later, I removed the box and found some of the foam had been chewed up to make nesting material.  Fortunately, little of the material was damaged, and I have way too much anyway.  (I had to buy the whole roll...special order.)

Back on the boat, I had marked any obstructions on  the three pieces that I removed, so I had the outlines of where the insulation could go marked on them.  To begin, I laid out the foam on the largest piece and cut a rectangle larger than what I needed.  Then, I could move the remains of the heavy roll out of the way and get to work.  The material is easy to cut with scissors or, my choice, a utility knife.

Using my predetermined lines as a rough guide, I trimmed the insulation to fit the space available on each of the three pieces of the engine box/steps.  The Mylar/foil facing is reinforced in a criss-cross pattern, so cutting is easy by following these lines. I cut first a shallow line through just the facing, to give me a better guide, and then two or three deeper cuts until the material was cut all the way through.  The soft lead cuts easily. 

This is the top of the engine box and also the top step.With the insulation cut to fit, I taped the exposed edges with foil tape.  The tape sticks well to the Mylar facing, but not so well to the exposed foam on the bottom side (it does stick, though--it's not like it's flapping around or anything).  This seals the foam around the edges and will hopefully prevent future deterioration and damage.  I tried for the smoothest application possible, but even my best efforts resulted in a few minor wrinkles here and there.  At the corners, I slit the tape so that I could lay the sides down.



When the insulation was taped up, I turned it over so the foam was facing up and sprayed on a heavy coat of 3M 77 spray adhesive.  Then I sprayed a similar coat on the plywood.  Carefully aligning the insulation with the markings on the plywood, I pressed it into place, taking care not to press so hard as to distort the lead or compress the foam.  After pressing the insulation into the adhesive all over, I further secured each piece with some #12 stainless steel pan head screws and fender washers.  I installed the screws just tight enough to dimple the top of the Mylar facing slightly, but not to compress the insulation.  This also ensures that there's enough of the fastener penetrating the wood to have an effective grip.  The mechanical fasteners are necessary because no adhesive will hold the heavy insulation up for any great length of time, and, while the adhesive is important too, the fasteners will just help hold everything tightly in place so that the adhesive is not unduly strained--particularly on upside down pieces.  I drove a number of screws through each piece, including the middle portions.

topstepinsulate.JPG (137624 bytes)This is the top step with the insulation in place.

This is the front of the engine box with the insulation in place.eboxfrontinsulation.JPG (129220 bytes)

This is the second step with the insulation in place.stepinsulation.JPG (140812 bytes)

Glissando, Pearson  Triton #381

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