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Old 22-02-2021, 23:00   #1
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Foam Covered Stringer in Fridge Foam

Well, the battle of installing a new fridge and freezer is fully joined at this point and I have all of the old materials out. I have been looking at the various posts for ideas but have a unique question.

In the cabinet where the fridge/freezer was installed previously there is a structural stringer which gets much closer to the freezer/fridge compartment than the rest of the hull.

I am working on 6" of insulation around the sides of the box and this stringer rises off the hull by about 3" and is about 6" wide. This stringer is about half way down the "sloped" side of the box and the fiberglass covering it is probably between 1/8" and 1/4" and is filled with structural foam. The foam is definitely dry. The stringer is well below waterline (as is most of the locker).

Trying to decide if I need to build a shelf in the fridge around it, put more foam thickness (which would make the thickness to the hull something like 9 inches but all of the other walls about 6.

Thoughts?
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Old 24-02-2021, 06:29   #2
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Re: Foam Covered Stringer in Fridge Foam

Thicker foam is always better.
The real trick is insulation with a real vapor barrier.
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Old 04-06-2021, 18:30   #3
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Re: Foam Covered Stringer in Fridge Foam

Ah but at 25" of foam one does not have many beers to consume before you have to add more :-)
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Old 04-06-2021, 18:49   #4
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Re: Foam Covered Stringer in Fridge Foam

So, at this point I have a good thermal model and assuming that the stringer has high heat conduction (i.e. the fiberglass over it is thick enough to be almost as good as if the entire block was steel and the stringer does not appear to have a huge impact once it has at least 3" of foam over it. That means a minimum of 5" of foam which I was planning for anyway.

In the end I could not use the 2nd to largest isotherm evaporator (i.e. the 54" x 12" one) due to limitations on exactly where it could be bent and getting it through the top loading hatch after the fridge was completed (i.e. if you don't build it in while making the fridge then it won't go) so had to drop down one more size. which fits comfortably and makes adding a bit more insulation here and there much easier.

In the end I have about 8" of foam under the freezer, 7" under the fridge. All exterior walls are 5", the sloping section against the hull is about 6" and the side against the hull is between 8" and 12" depending on which end. The insulation between the two boxes is 2"

In the end, I created a new outboard "bulkhead" which is 1/4" marine plywood with one layer of glass on both sides glassed to the upper stringer and the underside of the galley cabinet about 6" away from the hull at the top and against the hull at the bottom. This provides access to the outside of the insulation and makes routing the refrigerant lines now and in the future much easier.

Since most of the bulkheads were already covered in fiberglass I took the opportunity to cover all of them (first level moisture barrier) and provided a 1/2" access tube to the lowest point which is carefully sealed off under the floor (just in case moisture got between the fiberglass and the vapor barrier I would be able to do something about it without tearing everything apart).

I then used 6mm vapor barrier and 6" wide vapor barrier tape to carefully line the volume.

In California I was not able to get large sheets of blueboard, only 2x2 foot pieces of 1" thick sold as "hobby board" but verified it is the same stuff. So used 2" Rmax (isocyanate) to build up the interior until within 1 or two inches of the desired thickness and then did the last bit in expanded polystyrene (blue board) 1" pieces. Each layer had all gaps filled with foam in a bottle and then taped off with vapor barrier tape.

The interior is 1/2" marine plywood with 6oz fiberglass and epoxy resin on both sides prior to installation. I used west systems epoxy with 410 microlite filler (west claims it is not horrible insulation) on both the foam and the boards with enough to ooze out everywhere as I tapped the boards into place. I put a piece of 6oz 4" wide fiberglass in the 410 putty on each of the seams so there is some level of mechanical connection from the outside of the plywood.

Once I have sanded out the interior (luckily 410 sands very easily) I will use 4" fiberglass tape (6oz) to tape all of the seams. Sand the edges of the tape to bevel and then apply 6oz cloth over each face of the fridge overlapping the tape for the corners/joints. (I know, overkill but in sanding out the putty I have lost a bit of fiberglass)

The last question is if I should use Formica like I did on the previous boat when I did the same thing or if it will be easier to paint (either with west systems epoxy and white pigment or with 2 part LP.

Leaning toward the Formica as all of the faces are flat and I am tired of sanding :-)
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Old 05-06-2021, 13:20   #5
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Re: Foam Covered Stringer in Fridge Foam

Just one small comment: ime, sharp right angle corners in anything are grunge collectors. So, If you can find a way to radius those corners, perhaps with sealant, whoever has to clean the fridge will be grateful.

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Old 05-06-2021, 23:27   #6
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Re: Foam Covered Stringer in Fridge Foam

Very true, last time I used thickened g-flex epoxy with white pigment and a 3/8 radius (the back of a west system's mixing stick)
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