My original plan was to install 2" XPS (extruded polystyrene) sheets underneath the fridge box and against the hull. XPS is good at resisting water entry but has a slightly lower R value of R5. I planned on using polyisocyanurate on the inboard walls where I had less space for insulation. Polyiso is rated at R6.5 but it doesn't deal well with moisture. It also doesn't handle being cut and manipulated nearly as well as it tends to crumble. I decided to use it only on the inboard facing wall next to the sink, mostly because it proved to be a real pain in the ass. The rest of the walls in the fridge got the XPS treatment. Against the curve of the hull above the waterline where the sun hits the hull, I glued Reflectix onto the outward face of XPS boards and left about a one inch air gap between the hull and insulation. The idea is to reflect radiative heat transfer from the sun hitting the hull. I have no idea if this will make a difference but given the difficulty of matching rectilinear foam boards with the curve of the hull, I was going to end up with an air gap anyways, so I thought I'd take advantage of it.
XPS sheets being installed in the floor. The pink and blue sheets are both XPS, just different manufacturers.
Polyisocyanurate insulation installed on the inboard wall.
The reflectix insulation installed against the hull.
Given the oppressive amounts of cold beer and ice I plan on storing in this fridge box, I needed some structure to support the weight of the box. My goal was to provide some beefy structure without having to cut out much insulation. I ended up using 2" aluminum angle iron mounted longitudinally under the fridge box. I through-bolted epoxy covered brackets on the fore and aft cabinet walls and laid the aluminum beam on top of those brackets to sit flush with a layer of insulation. I used the same material mounted under the countertop to support the vertical walls of the fridge box.
Longitudinal aluminum angle iron support.
My construction process went a little something like this:
- First, I installed an epoxy covered wood standoff on the cabinet floor so if any moisture got into the cabinet, the insulation would not sit in it. I drilled a few weep holes from the floor into the bilge so water couldn't build up.
- I put a layer of builder's plastic against the hull. The idea was if the deck to hull joint or deck stanchion started leaking into the cabinet, it wouldn't penetrate the insulation. I didn't encapsulate the entire insulation in a vapor barrier because I've read that all that does is trap moisture inside the insulation. A more accurate way of stating that would be: I encapsulated the entire insulation in a vapor barrier THEN I read that all that does is trap moisture inside the insulation THEN I spent a weekend removing the vapor barrier and three tubes of silicon I used to hang the vapor barrier.
- The only option we had to run wiring for the compressor install is currently crammed with wiring and would require removing some wire to accomodate the compressor wiring. Given that I had 9" to 11" of space for insulation against the hull near the top of the box, I decided to install a wiring conduit in the back of the box. I'm not wild about this choice. Cutting the insulation around the conduit was a giant pain.
- Cut and dry fit foam for a single wall. This is a very iterative process when you have to work through the opening (oh, this perfectly cut piece of foam doesn't fit inside the opening) and when you have a complex curve and fridge box that steps down (oh, this perfectly cut piece of foam doesn't actually fit the space it's supposed to fit in).
- Once I got all the pieces cut and dry fit (and labeled, all the pieces start to look the same after a while), I installed the insulation for that wall. I caulked every seam and joint with silicon to make sure that there was no air passage through the insulation. Every gap larger than 1/8", got injected with spray foam. Here's a tip with spray foam: wear latex gloves and a long sleeve shirt when using this crap. You'll think you're being all super careful and cautious and then your wife will point and guffaw at the cabbage-sized glob of spray foam hanging on your elbow of which portions will remain stuck to you three days later.
- Once the spray foam cured, I'd trim it back down and coat any exposed spray foam with silicon. Spray foam doesn't like moisture either. One other note about spray foam: it cures with some pretty large air bubbles in it so don't depend on it for any large voids. I relied on it more as way to prevent air passage, rather than proper insulation.
- Once the wall was done, I moved on to the next wall. Lather, rinse, repeat.
- After all the insulation was in place, I caulked all the seams a final time with silicon to make sure no air was going to leak through the box.
The end result of all this foam cutting and fitting and caulking:
- 9" of XPS insulation below the fridge box.
- Anywhere from 5" to about 11" of XPS insulation against the hull.
- 4" of XPS insulation on the aft cabinet wall.
- 6" of XPS insulation on the forward cabinet wall.
- 3" of polyisocyanurate insulation plus 3/4" of layers of reflectix because I couldn't find 3/4" foam boards.
Bare fridge cabinet.
Plastic installed against the hull.
Floor insulation complete along with brackets for longitudinal support beam.
Aluminum angle iron acting as a support beam.
Inboard wall with polyiso insulation and then covered with Reflectix. You can also see the aluminum angle iron used as a support for the vertical fridge walls.
Forward wall complete.
Aft wall complete.
This was all the foam I used in just the top half of the outboard wall against the hull.
I think I cut about 30 individual pieces of foam to fit the outboard wall.
Insulation is DONE!
Sizing some of the foam pieces.
Our disaster of a cockpit during construction. I did all the foam cutting in our cockpit. Any attempt to cut foam on the dock ended up with foam particles in the water and that's no bueno.
If you feel that you just haven't gotten enough pictures of pink and blue foam, I took an extensive amount of photos and uploaded them here.