Where do I begin...
My original project
was to add insulation to my icebox
, which had been upgraded with two cold plates driven by engine
or 110V air-cooled compressors - they were split, meaning either could supply them.
Turns out the counter top was not only tabbed to the hull, it was back-screwed from the engine
room. Not only that, the cold box was machine-screwed to the top of the counter, but the nuts weren't locked down. That meant the screws to the top could not be removed because the nuts would spin; without the screws being removed, we couldn't get the countertop out, even if the other challenges hadn't been present.
We wound up cutting it all out and building a new floor where the old one had rotted from a leaking hose in the drain, along with a new wall on front and sides, before we replaced the counter top.
To all 4 sides, bottom and top, I added aluminum
foil (reflective barrier), battens made from door skin (convective barrier) and then 6 inches of extruded polystyrene board (pink or blue board, depending on Dow or Owens-Corning). The original box had conformed to the hull; I sprayed two-part (two cans looking like freon cans) stuff coming through two hoses through a triggered nozzle, water resistant polystyrene foam, VERY CAREFULLY (see prior comments about expansion), a little at a time until it was full, yielding 14" down to 6" as the hull curved, R value of 30 minimum throughout, cut off the lumpy extras, and slid the new top in under the cabinets.
I coated the extruded with epoxy
after cutting each piece to size, to help minimize any potential water intrusion (belt and suspenders; the poly is supposed to be "waterproof"), and did stair-step laps on the joints of the boards, to help make any migration of air more difficult, epoxying as I went. Laid fiberglass
on all surfaces, then gelcoated. Of course, the top went on after all the hardware
was installed; we went with a top freezer
(due to how it was set up/access), and front reefer, door, and double gaskets (one on the interior
level and the other at the door face level). Early pix in my gallery are largely devoted to this project
if you'd like a look...
I used a spillover fan in the center of the divider, with a matching air gap at the top in square inches (turned out to be an inch open space at the top), with dual Carel thermostats, the fan controlling the spillover volume into the reefer side, along with a keel cooler
and evaporative plate for the freezer
side. Both sections also have circulation fans controlled by the thermostats; when the cooling
cycle is happening, the circulation fans are running to even out the temps in the given space.
You will find a HUGE difference between tropical water and temps and more temperate zones; heat intrusion is what you're fighting, and your hull is the temperature of whatever the water is; inside the boat, it's whatever the air temperature is. Thus, it's entirely possible to run the compressor
double in the tropics vs cooler temps.
That said, we have a very efficient box, and the smart speed controller keeps the compressor running about 90% of the time, the most efficient for an evaporative system, at whatever speed is needed (less when less heat intrudes), to keep the freezer at 8 and the reefer at 32 F.
If you're serious about it, this is probably what you'll have to do to achieve your target. If you can get the top off, and the old box, along with the no-doubt useless insulation (if it's over, say, 20 years old), out, without having to go through what I did, it will be easier, but my build-out is an ultimate without resorting to vacuum panels
If you can get to the box, but don't want to cut it out, you may be able to add extruded polystyrene as I did, to the interior
. But even something as simple as some of the bubble-pack-looking stuff that you can buy at the home improvement stores will make a tremendous difference to your insulation qualities, if that were all you were to do.
If not any/all of the above, and you can find a space for it, the Engel reefer/freezers are very efficient. If you're going to be living aboard
the boat, refrigeration may well be your single
biggest energy cost; a serious review of your amps usage, and your ability to replace them, is in order, unless you go to engine-driven cold plates (not a very even temp solution).
Our electrical system
is heavy solar
, along with a Honda
eu2000i suitcase generator
which we can tie into our shore power
system when there's not enough wind
and sun. We do just fine in our semi-tropical location in the Bahamas
; our system as a whole was designed for the tropics.
I highly commend Richard Kollmann's book on refrigeration, and a browse around rparts.com for you to get a start on understanding what you're really up against. If you're going to be keeping the boat for any serious amount of time, it's well worth the effort and investment to do this part right...