Choosing the Perfect Refrigeration for your Boat

There’s no longer any reason to rely on frozen water to cool your food and beverages 
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Given sailors’ well-known liking for cold beverages and fresh food, a discussion of refrigeration options and solutions usually crops up sooner or later when cruisers get together. The choices are myriad and, having just gone through the selection process myself, it occurred to me that the way I made my own decisions may help you decide what will work best for your boat.

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Good insulation is vital to the performance

Good insulation is vital to the performance

There are three basic types of marine refrigeration systems: drop-in units that run on 12 volts and look like something you’d find in a house or an RV; cold plates that are installed in an existing refrigerator or ice box and run on 12 volts; and holding-plate systems that can run on 12 volts DC, 110 volts AC or an engine-driven compressor.

Make sure an air-cooled compressor is well ventilated, preferably via the bilge

Make sure an air-cooled compressor is well ventilated, preferably via the bilge

Each type has its advantages and disadvantages, depending on how you use your boat. A skipper living aboard full-time in the tropics, for example, will have different needs from one who is primarily a daysailor, but also spends a week each summer cruising Lake Huron’s North Channel.

Another factor to keep in mind is power: do you have hundreds of amp-hours worth of battery capacity and/or a solar charging system, or do you run a generator a couple of hours a day to keep your batteries charged? Be aware that refrigeration units can be real energy hogs, and you’ll need to be able to provide them with the juice they need to do their job.

Probably the easiest and simplest solution, if you have the room for it—and especially if your existing ice box has suspect or negligible insulation—is a drop-in refrigerator. These often resemble a “dorm-sized” apartment fridge, similar to what you would see at an appliance store. Examples include those manufactured by Dometic and Norcold, who make both top-opening and front-opening units.

Isotherm's SP water-cooling system

Isotherm's SP water-cooling system

To install, simply make the appropriate cuts in your cabinetry, slide the unit in place, and hook up a pair of wires. The boxes are already insulated and include attached air-cooled refrigeration systems. If only everything on a boat could be so simple! These units are an especially good choice for casual cruisers who have some skill with tools.

Rather than building your own coolbox, a drop-in box fridge with built-in evaporator may be an easier option

Rather than building your own coolbox, a drop-in box fridge with built-in evaporator may be an easier option

At the other end of the ease-of-installation spectrum is fitting a holding plate, like those made by Sea Freeze and Technautics, to an existing ice box. Holding plates—so called because they retain their cold temperatures for an extended period—are usually up to four inches thick and heavy, with a heft like they’re cast from solid metal. They are generally made from aluminum or stainless steel and contain rows of tubes filled with refrigerant that are surrounded by a liquid that freezes quickly. Once this liquid is frozen, the holding plate stays cold for hours afterward; it essentially behaves like a large block of ice on the side of your reefer box.

A holding plate system is relatively power hungry, so cruisers often operate it only when the batteries are being charged. In fact, in addition to a 110-volt or 12-volt compressor, these large systems often include a second compressor belt-driven directly off the engine.

A typical air-cooled compressor system

A typical air-cooled compressor system

An advantage of cold plate refrigeration is that it only needs to be operated for a short period each day. On boats equipped this way, I usually find that an hour in the morning and an hour in the evening keeps the reefer cold—which is about the same amount of time I run the engine or a generator to charge batteries anyway. If you are short of battery capacity, this may be a good solution for you. 

Because cold plates rely on thermal inertia, when installing one you should either replace or upgrade your box’s insulation, or be sure your existing insulation is in good condition, if one is to work well. The heat exchangers on these systems are usually water-cooled.

For my boat, I chose a BD series 12-volt air-cooled cold plate system from Sea Frost because it best matched my sailing style—cruising the relatively cool waters of New England.

The coolant lines are led from the cold plate and ready to be attached to the remote compressor; using a template to ensure the cold plate will fit the ice box; the cold plate hard at work—that’s the kind of temp you want to see! 

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This type of system is compact, easy to install and consists of a thin cold plate that is mounted in the ice box and connected to a compact compressor with a heat exchanger, condenser unit, mounted remotely. It is designed to be left on all the time to keep both the plate and refrigerator box at whatever temperature you set the system’s thermostat. Battery draw is such that a small array of solar panels or an hour or two of engine charging will easily compensate for the load.

When I spoke to Cleve Horton, who owns Sea Frost, about the fact that I wanted to upgrade my icebox, one of the first things he wanted to know was my expected cruising grounds. This, in turn, drove his recommendation of the air-cooled BD series, as it both fits my budget and is robust enough to keep things cool up north.

Because there is a remote chance that one day I’ll pull up stakes and head for warmer climes, he suggested I buy a unit that includes the option of adding water cooling later. Otherwise, the unit won’t have enough cooling power to keep the temperature down where I want it. For cruising in New England, though, he said air cooling should be more than sufficient for my needs.

It’s been a month now since I first turned on my reefer, and over several cruises my wife and I have enjoyed cold beverages and fresh food for the whole of each trip. I even keep a small container of ice in the bottom of my reefer and set the thermostat low enough to keep it in its solid state for more than a week. This to me is luxury cruising. It also has my wife thinking about expanding our cruising grounds. 

SYSTEM A

There are three main variants of pleasure boat refrigeration. In System A, an engine-driven compressor is linked to a cold plate—efficient, but depends on the engine running

There are three main variants of pleasure boat refrigeration. In System A, an engine-driven compressor is linked to a cold plate—efficient, but depends on the engine running

SYSTEM B

System B is the most common small-boat system: an air-cooled compressor with an evaporator or cold plate.

System B is the most common small-boat system: an air-cooled compressor with an evaporator or cold plate.

SYSTEM C

System C has a water-cooled compressor, more efficient in hot climates

System C has a water-cooled compressor, more efficient in hot climates

RESOURCES

Sea Frost
seafrost.com; 603-868-5720

FrigoBoat
frigoboat.com; 301-352-6962

Dometic/Aldler Barbour/Waeco/Grunert
dometic.com; 574-294-2511

Thetford/Norcold
thetford.com; 734-769-6000

Webasto/Isotherm
indelwebastomarine.com;
954-984-8448

Technautics/CoolBlue
technauticsinc.com;
619-609-3432

Sea Freeze
seafreezeinc.com; 360-733-8282

burton

Andrew Burton is a delivery skipper and
freelance writer who has logged more than
300,000 offshore miles. He can be found
racing his Shields class one-design or
cruising his C&C 40 in Newport

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