Rhumb Lines October 2013 Issue

The Great Ice Hunt

Photo by Ralph Naranjo

The Isotherm SEC is the latest in a series of “smart” controllers designed to maximize the efficiency of a 12-volt marine refrigeration system.

I remember where and when we gave up. Eleuthera. Summer. A day of vision-blurring, morale-melting heat.

Tosca’s crew hid under a slice of shade in the cockpit. Puddles of sweat at our feet. No one wanted to move, but the last cube in the ice box had turned to water. Something needed to be done. I set out in the dinghy for the nearest store, one mile up a dusty road.

We had no fridge on Tosca. Marine fridges were expensive—not to buy, but to own. The marine refrigeration world seemed evenly divided between undisciplined engine-driven fridge/freezers and anemic 12-volt models. Both pumped ozone-eating R-12. The most popular neighbor in every harbor was the retired air-conditioning repairman, making a tidy income chasing Freon leaks.

Still novices to the McGyvering arts of full-time cruising, we knew we weren’t ready for a fridge. We had trouble enough keeping the running lights working. But ice? We could handle ice.

The Bahamian storekeeper took my $5 and handed me a bag of cold water and some quickly vanishing cubes. Here was my 10-pound bag of ice.

“Dat ice come all de way from Gov’nor’s Harbour,” he said.

“Dat ice” didn’t even survive the dinghy ride back to the boat.

The cruising kitty was evaporating; we had to make a change. That was, so far as I remember, the last of the great ice hunts. Amazingly, our diet improved. We discovered a cornucopia of foods that keep just fine without a fridge.

Today, the era of reliable chilling is upon us. It has done wonders for crew morale, but cold beverages come with a price—in dollars and amps. In this month’s issue, we look again at “smart” controllers that automatically vary the operating speed on the omnipresent Danfoss BD series compressors. If you’ve got some amps to spare, the controller will kick the compressor up to maximum RPM, so it can cool as quickly as possible. In times when the ship’s batteries are overburdened, it will dial the compressor back. A digital thermostat tracks box temperature, further fine-tuning the cooling cycle.

As this month’s test and previous tests have shown, the gains in efficiency from these controllers are relatively small, most noticeable in the cumulative—a lower compressor speed day after day eventually translates into less engine run-time tomorrow. For the long-term cruiser who is putting an hour or more on his engine daily to keep the fridge going, these little savings can add up.

But as our tests (and the makers’ optimistic efficiency claims) have shown, we have a lot more control over our refrigerator performance without these gadgets than we might think. How and when you load your fridge is an often-overlooked part of the equation. The compressor works harder to keep ice in an empty freezer than in a full one, and no smart thermostat will instantly recover the energy required to chill drinks added on Day 3 at the anchorage. And as every cruising book on the planet hammers home, insulation, box location, and design are all vital factors in the cooling equation.

These new controllers are smart, but they can’t work miracles—and we still have to do a bit of thinking.

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