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There's no doubt that a way to keep things cold aboard makes your boating life more pleasant. Here's what you need to know.
Having some form of refrigeration aboard your boat is a godsend. It keeps perishables fresh, prevents milk from going sour, and, should you also have the luxury of a good freezer, can store ice cream for delicious relief on hot days.
If you spend a lot of time at the dock where shore power is readily available, or if you have an onboard generator that you use frequently, your best choice may be a 110v AC refrigeration unit. It's relatively inexpensive, dependable, easy to install, and should give you years of trouble-free service. Most boaters don't live at the dock, however. If you spend time cruising and anchoring out, a better option may be to use either a 12v DC unit or an engine-driven refrigeration system.
Here's what you need to know if you're considering adding or replacing a marine refrigerator aboard your boat.
What Is Marine Refrigeration?
Before getting into exactly what refrigeration is, it's important to understand what it is not. It is a common misunderstanding that refrigeration creates cold, but this is not the case. Rather, refrigeration is the transfer of heat from one area to another. Basically, all refrigerators work on the same principle: A gas is compressed and allowed to expand inside an evaporator (the plate that gets cold inside the refrigerator). As the gas expands it absorbs heat which is then dissipated on the outside of the refrigerator, either to air or sometimes through a seawater heat exchanger. The expanded gas then passes back through the compressor and the cycle repeats. Although there are some exceptions, which we'll cover in a moment, most refrigeration systems consist of six principle components: compressor, condenser, expansion valve, evaporator, refrigerant, and thermostat.
Types Of Marine Refrigeration Units
There are three main types of marine refrigeration units: 1. Self-contained units (all-in-one or split systems), 2. thermoelectric, and 3. holding plate systems. Each type has positives and negatives depending on your boat, where you boat, and your marine refrigeration needs.
Self-contained marine refrigeration units. The easiest type of marine refrigeration unit to install is a self-contained unit that looks very similar to one you may have in your home. All the components are typically built into the case with the compressor sitting on a metal tray outside and below the insulated cabinet.
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Other self-contained marine refrigeration units are a 12-volt DC split system with the compressor and other components sometimes a fairly considerable distance from the insulated box, which only contains the evaporator plate. Many of these systems are available for DIY installation, with converting an icebox to proper refrigeration a popular upgrade.
The simple installation of only two major components — compressor and evaporator — make these units very popular, and they have greatly improved in recent years. The compressor cycles on and off as the box warms and cools. The amount of time it runs depends on the unit, whether it is raw-water or air cooled, and the amount and type of insulation encasing the cold compartment. While these units draw relatively little current, the total amperage draw over a 24-hour period can be more than the boat's electrical system can handle. A close evaluation of your boat's battery size and recharge capability is in order when installing a 12v DC refrigeration system.
Thermoelectric systems. Thermoelectric refrigeration is the exception to the rule and uses no refrigerant. It is also 12v DC powered but uses what is known as the Peltier effect and has no moving parts except a heat-dissipating fan. These quiet units can last a lifetime, and installation is simple, but they're not for every boat. They're far less efficient than other types, requiring more amps to cool a box. They'll cool the box to 40 to 50 degrees below ambient temperature, which is inadequate for the tropics and other hot weather areas, and possibly not worth the power drain.
Holding plate systems. Engine-driven systems with holding plates are the most powerful system for those wanting deep freezes and lots of ice. The compressor typically runs only once or twice a day for short periods, assuming adequate insulation in the box. However, the initial cost is far more than the cost of a 12v DC unit and it is more complicated, so there's a greater potential for problems. If you consider an engine-driven compressor, factor in the cost of labor of mounting the compressor on the engine itself rather than on a nearby stringer. This allows the compressor to vibrate and move with the engine, resulting in less wear and tear on bearings. Also consider that you will not want the compressor to block access to other components. Usually this type of unit is installed by qualified professionals while other types of 12-volt units are easier to install by a "do-it-yourselfer." Some units have two refrigerant channels in the holding plates with the option of separate AC or DC run compressors for use when plugged in to the dock.
Look for marine-grade construction materials. Most holding plates are made of electropolished or powder-coated stainless steel which is corrosion-resistant and attractive. Water-cooled condensers exposed to seawater should be made of a noncorrosive material such as cupronickel. Marine-grade materials add to the initial cost of the unit, but if you're going to make this kind of investment, buy a dependable unit that will last. Check the manufacturer's warranty — longer is better.
Powering A Refrigerator
There are basically three options when it comes to powering refrigeration: 1. AC units that are powered either from a shore power connection or generator, 2. DC units that run from a boat's battery bank, and 3. engine-driven units that have a compressor powered by a belt running from the engine.
Most 12v DC units come with an air-cooled condenser, although a water-cooled condenser, often an upgrade, is preferable, especially in warmer climates. Water cooling is more efficient, so you get greater cooling capacity with a smaller unit, and they can be installed almost anywhere. Air-cooled condensers must be mounted where they can be ventilated to dissipate the high heat removed from the ice box. For 12vDC running at dockside, simply plug in your battery charger and replace the battery power you're using. Away from the dock, your primary consideration is how often and how long you must run your engine to have ice and cold food. Having a dedicated battery bank for your refrigeration unit is a good idea, but remember that you still have to run your engine, generator, or have a wind generator or solar panel to recharge the battery. You can increase your options with an AC/DC refrigerator or icemaker. The dual-voltage units switch from AC to DC automatically when the AC power source is shut off.
Converting An Icebox
If you plan to convert your existing ice box to a refrigerator and/or freezer using a conversion kit, pay special attention to the box's insulation. Heat loss through leakage can be cut in half by increasing the insulation from 2 to 6 inches. Most refrigeration manufacturers will be happy to provide you with good information for properly insulating and/or building an ice box for use with their units.
Portable units can be a popular alternative for some boats that do not have space for a permanently installed refrigerator. They're a smaller, lighter, and a convenient alternative to hauling that heavy, bulky cooler of ice on every outing. But, typically, they don’t cool as well as a permanently installed unit.