I have been where you are now, taking 3 months to build three new boxes in 2005. This is what I discovered and how I did it:
First, reset your brain, purge all your current
thoughts about the project
, just while reading the rest of this post. After that, compare and make your decision.
My first discovery was that vacuum panels were not going to happen. Even the Rparts panels (which are way cheaper) were still outrageously expensive. I could afford it but realized I was not crazy enough to spend that much money
on this. VIP's were quoted at $7,800.- to get the idea.
So, what I want to say is that it is much better to have a smaller box with more insulation than the other way around. If you plan to sail into the tropics and not run a genset hours each day, design a fridge with 4" foam and a freezer with 6". A 6 cubic feet box with a BD50 compressor
unit will run about 20 minutes each hour, a duty cycle of 1:3. This is for both freezer and fridge because the freezer has more insulation and is opened less.
Start with the selection of foam. Use pure refrigeration
foam, 2" and/or 4" thick, no reflective coatings or plastic lining or whatever, because you are going to have several layers and you don't want anything in there that conducts heat better than the foam. Use expanding spray-foam as the adhesive
Now, you have to make a rectangular outer box where you can put the foam in. When the space for the box isn't rectangular at all, like against the hull
, use 1/8" plywood
, some 1"x1" battens and a tacker to create the biggest possible rectangular box. You will remove it later, so nothing fancy. Use the 1"x1" battens for the corners but also for plenty supports/struts inside the box to keep it in shape. So, give the box a bottom but no top.
Next, use spray glue to put plastic foil on the outside of this wooden box, except the bottom of course (can't reach it). Use epoxy
and roller and brush to coat the inside of the space around the box (like the side of the hull
, inside of front-cabinet wall, etc.) Let the epoxy
gel to the "very sticky" phase and use it at that moment as the adhesive
for aliminium foil, which you put in with the shiny side out (shiny side facing the hull). The epoxy and foil are the moisture barrier and the radiation barrier.
Next, measure one outside of the box (largest measurement) and cut a piece of foam. Parts
, like the bottom edge, will need to be tapered. This is easy, use a bread knife and a surform rasp. You can get it to fit pretty quick and every panel will be faster. Spray some expanding foam on the bottom edge (or just into the space down there) and put the panel in. Use masking tape at the top to hold it against the plywood
. Keep going on until all is filled up. After that, remove the plywood and plastic foil.
You are now left with a big hole where the bottom should be. You can use sheet-foam or pour 2-component liquid expanding foam (but go slow, 1 mixed cup at a time). Use the surform rasp (after fully cured) to shape it when pouring went a bit out of hand.
Now is the time to decide on minimum isolation thickness and interior
volume. I would advise a maximum of 6 cubic feet interior
. You make it smaller by putting in more panels on the sides and bottom.
Next is the lining. Easy but time consuming when you want it to look pretty. Start with a sheet (or half sheet, do the math and jigsaw puzzle on paper first) of 3/8" marine
plywood. Put it on a level bench or A-frames. Using a black permanent (thin point) marker, draw out all the panels you need for the inner lining. Make the bottom piece the full size so that the walls stand on the bottom.
Don't use the existing edges of the sheet (stay a half inch away from them) anddon't cut yet! Vacuum it.
Drape the lightest fiberglass
cloth over the whole panel (in 1 piece) and cut it so that a couple of inches hang over the sides, like a table-cloth. Now start mixing batches of epoxy resin + fast hardener. Pour the first batch (6 pumps if using West System is a good start) in the center of the sheet and use a plastic spreader to spread it. It must become completely transparent without trapped air. This is really easy. Works all the way to the edges and ignore the overhang. Let cure until gelled (still sticky) and add another coat. If the spreader becomes difficult to use, switch to a roller. Continue this process (start in the morning) until the cloth is completely under the epoxy. Let cure for 24 hours; it'll look like a varnished panel and the cloth is only visible at the overhangs.
Cut away the overhang with a sharp knife and smooth it with very course sandpaper (don't cut yourself on the edges, very sharp). Turn the panel over. Use brush and roller to coat the backside and edges with epoxy (fast hardener again). Let fully cure. Dry-sand (wood fibers come up after first layer of epoxy) and coat again. Let fully cure.
Turn panel over again and wet sand it (with orbital sander). Hose it wet and sand; rinse with hose and look how the water
flows over the panel: look for any "rapids". This is where you must sand more. Stop sanding
when you hit the fiberglass. This is where you decide how pretty the end result must be. You can roll on more layers of epoxy or decide it's good enough.
About the wet sanding
: only use the machine when the hose is away and excess water
is off the panel. Use a double-insulated sander, which is every modern one I think (label on sander states that with 2 square symbols, one inside the other).
Now you cut the panels. The lines drawn on the wood are as clear as before the epoxy and glass went on.
Put the panels in the box, using very little spray foam (just couple of dots) to hold them in place and immediately put some struts in to force the walls onto the foam. Don't put the top on yet. Use angle to check it is as straight as you want and don't worry about some small openings where they meet. Use thickened epoxy to put fillets in. I used Coloidal Silica to peanutbutter consistency and those West System fillable caulking tubes for a quick job.
Now you have the best excuse in the world for buying
the Fein Multimaster tool. You can get sanding attachments to sand the fillets to perfection. Alternatively, use a short piece of hose with sandpaper around it but I ended up with RSI from that job.
Sand everything incl. the underside of the top. Now you can paint
it, the top still off the box. I used Awlgrip which is safe (but still not food
grade may be) after cure. Don't use white paint
Now, drill the holes for freon lines. The connectors of the evaporator determine the size. Mine just fit through a 1-1/4" thin-wall PVC pipe. Use PVC pipe, it's the moisture barrier at the most important spot because the freon lines will create condensation
. I used a 10" long 1/4" drill bit to drill a pilot hole through the whole lot first. Next was the hole-saw from both sides. I used the PVC pipe itself to cut away the foam. Make the pipe 1/4" too long so that each end stick out 1/8". Use silicone sealant
to close the gap around the pipe... do this good, absolutely watertight.
Install evaporator, sensors etc. as the top is still off so easy access. I installed compressors and everything at this phase and tested the system to be sure all the equipment
was good. Afterthat, I used silicone sealant
to put the top on (don't use stronger, silicone is tough enough and leaves hope to get it off later, if ever needed).
Now, you hopefully didn't forget room for the insulation at the top I hope. Put the sheets
on, level the surface with batten and surform rasp. Now, stab the bread knife in what you think is the center of the opening and start cutting to a side. Cut the opening out. Epoxy brush/roller the foam and aluminium again. Should look like a spacecraft part now. Fit collar, lid and counter top, ready!
Some detail photo's attached.