Refrigeration Refit, Part III: Frigoboat Keel Cooled System

In Part I of my refrigeration refit I discussed installing new insulation. In Part II, I discussed rebuilding the fridge side door.

In this last part of my refit of our refrigeration system, I replaced the mechanical systems in both the fridge and freezer so it could finally get the beer cold again.

Originally, both boxes had their own Adler Barbour Super Cold Machines, which were seawater cooled, 12 volt systems with evaporators that looked like holding plates. The compressors were in a compact, poorly ventilated compartment next to the stove, whose heat definitely didn’t help things. The seawater pumps were fragile 12 volt pumps that easily lost their prime, added another amp in power consumption, only lasted a few seasons, were expensive to replace, and added to the list of systems requiring winterization. I’d given up on running the pumps while underway because of how easily they lost their prime… but then the efficiency of both fridge and freezer dropped significantly when running on just air cooling. Running on air cooling was so ineffective the freezer run continuously but still wouldn’t stay frozen. The fridge compressor also ran continuously with air cooling, becoming a giant power hog on the batteries. I probably could have hired a “fridge guy” to look at some of my problems (if I could find one), but I really wanted bigger improvements.

Later Catalina 400s use one air cooled compressor mounted in the aft lazarette, forgoing a separate freezer box entirely. With sufficient airflow, air cooled systems can be pretty efficient and reliable. I very seriously considered going this route, but liked the idea of Frigoboat’s Keel Cooled system from Coastal Climate Control.

Keel cooled systems are pretty elegant. Instead of the refrigeration heat exchanger getting cooled by air with a fan or with seawater pumped through it, the heat exchanger sits in a hunk of metal just outside the hull, bathed in seawater. No fan or water pump is needed, so the compressor can be mounted in a space with poor ventilation. In a way it’s “another hole in the boat,” which is sorta bad, but it’s not quite a thru hull… there aren’t water hoses connected to it that can sink the boat. Galvanic issues need to be attended to, but this isn’t too difficult in fresh water.

There are a few installation constraints I had to consider. The compressor can be mounted a long way from the evaporator, and tubing extensions are available to get the length right. The keel cooler, however, only has a five foot long pair of tubes that connect to the compressor, and this can’t be extended… so the compressor needs to be pretty close to the keel cooler. Additionally, the keel cooler can’t be smushed by any lifting straps or cradle pads during haulout, limiting where they can be placed on the hull. I also wanted the anodes on the keel cooler accessible without scuba gear to make changing them much easier, but they have to at least stay very wet when heeled.

Eventually I figured out a location on our Catalina 400 that fulfilled those requirements. I mounted the compressors in the storage area under the starboard settee, with the keel coolers nearby under the salon table. Changing the anodes will require snorkel gear if not done at haulout, but it isn’t at risk of being far out of the water when heeled.

The evaporators shipped as flat plates that I had to carefully bend to the right shape to fix our fridge boxes. Coastal Climate Control provided excellent instructions for this process. I know it is said, “measure twice, cut once,” but I probably measured twenty times since each evaporator costs over $300. After laying each evaporator flat over a soft towel on my garage floor, I kneeled on a piece of 3” pipe supported by wood just thicker than the evaporator. I used a heat gun to carefully warm them to prevent kinking or cracking of the finish as I carefully bent them to shape.

The evaporator tubes follow the same path as the fuel tank fill and vent hoses, cross over the fuel tank, then connect to the compressor and cooler tubes. Installation definitely required two of us as I didn’t leave much room behind the insulation. We also needed to be very careful not to kink a tube or get any contamination on the connectors.

Since I had been frustrated with large temperature swings with my old system, I also chose a digital thermostat from Coastal. I mounted their displays in a galley cabinet, and they show the current temperature of each box. The temperature swing, as well as a few other variables, are user programmable.

Real World Testing

Redoing our entire refrigeration system was a time consuming and expensive process, but we’ve been very happy with the results. Kristin usually can’t eat most ice cream, so we brought some that she could eat with us on our North Channel cruise last year. About two weeks after provisioning at our home port and never spending the night at a dock, on a warm evening Kristin and I enjoyed ice cream while anchored in Lake Huron’s North Channel. Ice cream! On a boat! And it hadn’t melted!

Power consumption is significantly lower than our previous system. Unfortunately since I changed so many important components of the system at the same time, my comparisons of old vs. new aren’t very scientific. My old systems used a whopping 80-100 amp hours each per day, whereas the new systems use about 80 amp hours per day combined. That’s a 50% drop in consumption while getting much more consistent temperature control in both boxes! Amperage is much lower during each compressor’s “on” cycle, too, so peak amperage is much lower than before. On sunny days we have excess energy from our solar panels.

The temperature control is also excellent, with not much temperature “swing” in each cycle. I installed the temperature sensors to try and get accurate readings without damaging them. I’ve continued to monitor the system with my Acu-Rite fridge thermometer, which shows the temperature range of each box wirelessly.

Additionally, our new system is significantly quieter. The old water pumps and cooling fans produced a nearly continuous machine sound, and definitely weren’t “peaceful” in some of the quieter anchorages we stay in. Now, the noise of the new system is barely perceptible even on very quiet and calm nights. A slight “bubbling” sound can be heard when the door to the fridge or freezer is open, but obviously we don’t leave it open for long.

It also requires nearly zero maintenance other than monitoring anode consumption. Since we’re in fresh water right now I use aluminum anodes from BoatZincs.com. After two seasons, it seems that my anodes will only be replaced every 2-4 seasons.