Refrigeration for the Tropics
In the winter of early 2009 while I was trudging around an alternately frosty and muddy boat yard on the south coast of England preparing Camomile for our adventure, I was advised by an itinerant yottie who had been to the tropics that I would regret not fitting well insulated water cooled refrigeration before I set off. He was right but somehow, and much to my chagrin, his message was lost on me as icicles formed on the hull and neither the heating nor multiple layers of socks kept my toes from going blue.
It is more than possible to survive long passages and whole seasons without refrigeration by following appropriate strategies for stores preservation, diet and lifestyle. Arguably it can also be healthier, however, so far among the hundreds of cruising yachts we have come into contact with I can only think of two that took this option. There is a good reason for this. It is a whole lot easier to eat well when you have a fridge/freezer!
So Camomile had two separate fridges in her galley when we left the UK. The mighty original Westerly icebox must have been around 250 ltrs and came complete with a pump for removing the melt, an evaporator plate in the upper section, less than 50mm of slightly dodgy PU insulation and was located in the aft section of the galley.
The other was a new Waeco model which came as an integral unit and which I fitted outboard of the galley sinks where there was a void big enough to swallow the 60ltr fridge/freezer unit leaving plenty of room for air circulation.
Both units were air cooled, the icebox condenser venting into the deck locker and the Waeco venting into the galley. Heading south we had to reduce the degrees of latitude before it became obvious that the power consumption of the two units on a boat without a diesel generator to feed them was excessive and, to add insult to injury, were blowing all their heat into a boat interior that was already getting tropically hot, sticky and sweaty. By the time we arrived in New Zealand we had both had enough so I decided to modify the system.
The Waeco, with it’s built in evaporator plate, efficient insulation and up to date compressor/controller seemed effective however it was still perceptibly warming the galley ambient where the resident slave was becoming rebellious as a result.
To solve this I lead an extractor vent to the locker and routed it up and out of the deck locker to a solar extractor vent by the cockpit.
Over a period of time I found that this extractor was not particularly effective and so beefed up the airflow by placing two 12v computer cooling fans spaced well apart inside the tube.
These fans draw very little current and are wired into the Waeco unit such that they run when the compressor does. As there is plenty of accessible cool air down low in the bilges nearby to the unit’s condenser this now seems to solve the hot galley and improve the power consumption of the fridge/freezer.
The Westerly icebox was not going to be nearly so easy. After some experimentation it was clear that the PU “gap filler” foam I had injected into the cavities between the cabinetry and the outer skin of the icebox was not having much impact so I decided on taking more drastic measures.
Firstly I decided to reduce the internal size of the fridge by adding insulation inside and “bulking out” its impractical sloped bottom. I did this by cutting firstly a layer of 35mm PU insulation foam board and gluing it into the fiberglass icebox interior adding more thickness wherever it made the interior shape more practical.
I then added an even layer of the more expensive but very efficient 32 mm argon blown green foam over this.
I then laminated 2 layers of fiberglass over the foam to toughen and seal the surface.
It was then filled and faired with epoxy filler before painting with a “one pack” primer and white topcoat. I figured that this gave a minimum of 150mm insulation when I take into account the gap filler and original Westerly substrate.
I considered blocking the pump out drain at the bottom because of its probable action as a heat sink but in the end was persuaded that it would be more hygienic to leave it open for cleaning and draining out any condensate. Instead of blocking it up then, I insulated the drainage tube and created a plug to act as a baffle which seems to work well as far as I can tell and certainly makes keeping it clean and dry easier.
Secondly I decided that the lid needed to be better sealed and insulated. I applied two layers of green foam to the underside of the lid and rebated both this and the acrylic cover to produce a primary seal and a secondary sealing system to ensure that it kept the cold where it belonged. Finally, after I had used this reduced volume and better insulated system for some time I decided that the old compressor of late ‘80s vintage needed updating too.
I should say at this point that I am not a great fan of raw water pumped cooling systems as they seem to get clogged fairly regularly, particularly when copper antifoul is present, and consume power doing it. For this reason I decided to go with a “keel cooler” type where no pump is required.
I chose the Isotherm SP Self-Pumping refrigeration system which uses a special thru-hull fitting with a built-in condenser/heat exchanger. The SP fitting is similar in principle to a “keel cooler” through which heat is conducted into the water outside the hull. To increase efficiency, the SP design takes advantage of every movement of the boat to produce the “Self-Pumping” cooling action.
The SP fitting replaced the existing and poorly performing galley sink drain thru-hull with a larger and more effective diameter drain however it did call for a 60mm diameter hole in the hull. The SP system consists of three components: the Danfoss compressor with a modern control system, the thru-hull fitting, and the evaporator or holding plate. The holding plate mounts up to 3m away from compressor however the compressor installs slightly less than 1m away from thru-hull fitting. Fortunately I discovered yet another void large enough for the compressor just behind the gimbaled cooker which was well within this constraint. The system elements connected up using self sealing connectors to make the job easy, avoiding using soldered joints in close quarters.
The most stressful part of fitting the system turned out to be drilling the 60mm hole in the hull which I did while dried out on a pile and Yachtlegs and could therefore see the incoming tide while I was furiously assembling the fitting!
In summary Camomile now has two adequately efficient means of refrigeration which are independent of one another save for the power supply. Our solar arrays are capable of running both these systems together in sub tropical waters and are supported with fairly minimal engine running time when we are in warmer tropical waters or, alternatively, one or the other can be switched off and hibernated when supplies are low leaving the other with a full load and thereby operating more efficiently.
My recommendation therefore to anyone considering spending significant time cruising in the tropics would have to be the same as I ignored at the outset even if you are packing a diesel generator in your inventory.
To Westerly fridge owners, which are, as one Sealord owner put it, “designed to keep English beer warm in the winter”, I say – come aboard and have an ice cold one on me, I wouldn’t give a XXXX for anything less!