(Boat nerd post. You've been warned...)
Since we're employed and functioning members of polite society, we only have weekends to really get anything done on this fridge project. And since all work and no play makes Jack a dull boy, we keep scheduling our weekends with things that are more fun than building a fridge (like drinking wine and hanging with friends we haven't seen in ages). We should be done with this project sometime around Christmas. 2012.
I have been working on the design of the fridge box (click here for the plans I drew up for the fridge box). I don't really like fridge interiors that follow the curve of the hull. Ours was like that and it was *impossible* to have any sort of organization to the food as it all eventually ends up in a big pile. It felt like I was rumaging through a dumpster looking for something good to eat. So on the side of the fridge box next to the hull, we'll step the box down giving us a useful shelf. The lowest area of the fridge box, we are calling the "beer can well". It will be the depth of a can of beer, allowing us to pack the bottom of the fridge with cans. This guarantees we will always have something cold to drink, makes a flat space to load the rest of the food in the fridge onto and provides a sort of alcoholic holding plate to store negative BTU's between compressor cycles.
We also want to make sure that at the closest point to the hull, the box is at least six inches away. This should give us a good buffer of insulation so when the hull heats up from the sun, the compressor shouldn't have to work quite so hard. Most of the hull above the waterline will have between 8 and 10 inches of insulation protecting the fridge box.
At the floor of the box, I am going to put in epoxy-coated 1"x1" firring strips and then an epoxy coated piece of 1/2" marine ply. This will keep the insulation off the floor of the box in case any water does penetrate. There is a stanchion on deck that if it leaked, would leak into the fridge box. I'll probably provide a tiny drain hole into the bilge so water can't build up. All of the insulation will be encapsulated in overlapping sheets of builders plastic.
For insulation in the bottom of the box, I'll use 1" extruded polystyrene foam boards (XPS). Their R factor is a little lower at R5 but they are more resistant to water entry than other foams. Since I'm replacing a huge fridge box, I'll end up with around 13 inches of insulation at the bottom of the box so I'm not really concerned about R value for this insulation. I'm going to use XPS for the insulation against the hull since that's another area that's more likely to have water intrusion.
For insulation on the inboard walls, I'll only have about 4" of insulation to work with. I'm going to use polyisocyanurate there since it has a higher R value (R6.5). The downside to polyiso is that isn't as moisture resistant as polystyrene. However, it is lined on either side with aluminum foil. Once I cut the pieces, I'll epoxy coat the ends. Along with encapsulating it in 6mil builders plastic, that should keep the moisture out.
The existing fridge lids are just 2" of wood, held open by collapsible springs of death. When you have your head stuck way down in the box and accidentally touch one of the springs that hold the lids open, they come crashing down like Vlade Divac in the paint and 8lbs of solid wood lands squarely on the back of your head. Ask me how I know. We'll be replacing these evil contraptions with gas springs. I'm also going to add at least an inch of insulation to the bottom of the lids to give it a little better R factor.
In the end, we will have reduced our 11 cu.ft. fridge/freezer down to a well insulated 4 cu.ft. of fridge space and 0.6 cu.ft. of freezer space.
We got a rare sunny day that lit the hull enough to figure out where the waterline was. We marked it for posterity.
Our fridge box mockup including our highly specialized measuring equipment.
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