img7359One of the great luxuries of sailing, particularly in lower latitudes, is a cold drink with ice cubes cheerfully tinkling in your glass. Or perhaps an ice cream sundae on a hot afternoon at sea. With well-thought-out refrigeration, such frigid treats can be a reality.

Until recently, such luxuries as ice and ice cream were possible only on very large boats with impressive, if not unlimited, power driving serious refrigeration units. When Adler/Barbour introduced the first Cold Machine almost 20 years ago, it revolutionized onboard refrigeration with it's affordability and low power consumption, and such treats became a reality on offshore boats. At this point, the options available to the sailor were either these small air-cooled, non-holding-plate units or larger, expensive engine-driven holding-plate units. Since then, variations on these themes have been developed, but the basic principles have not changed.

Refrigeration is governed by basic laws of physics, and the bottom line is that the more energy one puts into a system, the more BTUs (or heat) will be removed. The goal of refrigeration manufacturers is to maximize the efficiency of their equipment to (1) reduce the amount of electricity used and (2) reduce the running time to maintain a cold box.

img7358The first issue is addressed by using more efficient motors to drive the compressors, or change the linkage between the motor and compressor. Further efficiencies can be gained in the heat-exchanging materials and qualities of the evaporator or type of fluid used in the holding plate. Small units are typically air-cooled rather than water-cooled for simplicity and cost-effectiveness. But air is a very poor medium for heat exchange, so opting for a raw-water loop is the choice of some. However, this is a bit of a catch-22 because, while the cooling efficiency improves, additional power is required to run an electric pump to circulate raw water, not to mention maintenance considerations and more holes in the boat to draw and exhaust seawater.

To sum up, there really are only a couple of basic refrigeration choices for the sailor, with a few variations within those choices. Also, a note on current refrigerants and legislation regarding them: Due to environmental concerns over chlorofluorocarbons (CFCs) and the depletion of the ozone layer, only authorized technicians with proper recovery equipment are permitted to handle refrigerants in their raw state. Freon with the designation R-134A has become the current standard in both the automotive (air-conditioning) and marine fields and is not available to unlicensed persons.

img7357I agree with Nigel Calder, who wrote in his excellent Refrigeration For Pleasureboats that servicing any refrigeration unit is no longer a "do-it-yourself" prospect and will require the assistance of a licensed tech. Yes, a handy sailor can install any of the pre-charged systems (we'll get to them later), but if a leak occurs or a dryer needs replacing, a service tech will have to be called in to pump down and recharge the system. Gone are the days when we could carry a couple of "Cold Shot" one pound cans of freon and top up a system with a pesky leak from time to time. However, all of us should be familiar with principles of refrigeration and invest in a good set of gauges, with manifold, to monitor the health of a system and perhaps troubleshoot a problem.

The most critical consideration in selecting a type of system will be to analyze just how you use your boat (short daysails, liveaboard, or extended voyages) and what your needs and habits are. Do you need to leave the boat periodically and maintain perishables, or keep a freezer at sub-zero 100 percent of the time? You may find that - although a high-capacity and high-priced system seems appropriate - a simple, less expensive unit will suffice if you have the necessary juice.

We recently completed a round-trip to the Caribbean with a small air-cooled unit that ran a lot of the time. We did not run the engine any more than we normally do (swinging a 90-amp alternator with 315 amp-hours of battery), and when we arrived, we still had frozen meat in the bin! The added bonus was that cold could be maintained while the owner was absent and the boat was in a slip.

Bear in mind, too, that the most critical component to any refrigeration system is the quality of the box and doors/lids. All of the manufacturers with which we've been in touch have their own technologies and techniques for tweaking their systems to make them better and more efficient. However, these gains, while very desirable, are far less significant than a truly sound box that keeps the cold in and the hot out.

For simplicity's sake, we'll break down the available systems into categories:

1. Hermetically-sealed DC compressor motors mated with either bin-type evaporators Motor size is generally in the 0.10-horsepower range. Amperage draw is 4 - 6 amps@ 12VDC, but running time may approach being continuous if the box is poorly insulated. On the price order of $500 - $2,000; can be owner installed.

2. Electric motor (DC or AC; generally .5 - .75 horsepower) driving a compressor directly or via belt, mated with holding plate(s). DC current draw may be in the 30-amp range, but running time will be 1to 2 hours per day. Price on order (installed): $4,000 - $8,000.

3. Engine-driven compressor (with electromechanical clutch) mated to holding plate(s). No electrical drain, but cooling time requires that the engine be running. Installed price: $4,000 - $8,000.

Hermetically sealed compressor and motor: These low-cost combination compressor/electric motors are identical to the motors you have in your household refrigerator, with the exception of the type of current (110V AC at home). This equipment is quiet, small in size, and quite dependable, but runs for a large part of the day. However, we do have to deal with a harsher environment aboard than at home, as well as vibration and power variations. We also do not have an unlimited source of power on board.

The upside of these units are low noise, low cost, simplicity, and ability to plug in at dockside and let the unit run while the boat is left unattended. Or, with a good wind generator or array of solar panels, the system will keep perishables cold when it is left unattended. The downside is high accumulated current draw over a long period of running time, low efficiency due to air cooling, and poor serviceability of components.

These units are pre-charged by the manufacturer and do not have easily replaceable dryers or proper service ports for a set of gauges. If there is a problem, it is generally easier and more cost-effective to simply replace the entire compressor unit. This type can be joined to either a "bin" or "thin-wall" type of evaporator (for more continuous running), or a beefier holding plate that is associated with heavier-duty units. The "bin" evaporators will require a compressor motor in the 0.10-horsepower range, while a holding-plate system will require up to .25-h.p. to chill to a proper temperature over a shorter period of time.

A thermostat is used to maintain temperature on both systems. Because of the constant running nature of these low-horsepower units, they tend to be the least energy efficient systems. If every milliamp used is critical, this is probably not the way to go. If there is an ample source of power, and if, as on a smaller weekender, the use is not constant, a small DC system has merit.

Excellent hermetically-sealed DC units are offered by Grunert (Marine Air Systems), Adler/Barbour (Kenyon Marine), Technautics, Isotherm, and Frigobar, to name a few. We should note that Technautics, Inc. has brought its equipment one step further by adapting a true eutectic plate system that uses expansion valves rather than capillary tubes to cool the plate. As this appears to be a real advancement, we expect the rest of the field to carefully monitor how well it works.

Electric motor driving a compressor: The second category deals with the larger horsepower motor driving the compressor. Linkage between the two is via pulleys and belt, or a direct (axial) drive that reduces noise and vibration. In either case, the motor and compressor are independent, so can each be replaced, independent of the other, if necessary. Because of the larger capacities of the components, this configuration lends itself to larger refrigeration capacities and combination refridge/freezer plates, linked together.

With this type of system, the components are located independently and then plumbed. The system is then evacuated and then charged. Technician required! However, once these systems are up and running they, because they are tailored specifically to a boat, will likely run forever - and if they don't, each component is accessible and serviceable.

The crucial differences between these and the previously discussed units is that they can be more powerful by design, and can create a more unique freezer/fridge arrangement, but do require a tech to charge the system. Glacier Bay, Grunert, Sea Frost, and Crosby (Kenyon Marine), are the primary suppliers of this type of equipment in the U.S. All use high-quality components and, because of the custom nature of the installations (tech required), do have design engineers to assist with your project.

This type of system draws a lot of current - on the order of 30 to 40 amps at 12DCV startup. Therefore, it is not entirely practical to leave this arrangement for any length of time unattended. Alongside, no problem. But on a hook or mooring for more than a few days, you will have a battery problem unless augmented with wind or solar generators. Better to put a timer in the system so you can limit the amount of time the system can run during a day, depending upon what can be anticipated pumping back into the system.

Engine-driven compressor mated to holding plate(s): The third category is the engine-driven compressor, which eliminates any electrical needs. However, it will only run while the engine runs, eliminating any possibility of maintaining perishables while leaving the boat for any length of time. These systems are custom by nature, with individual components, and do require pumping down and charging by a technician. However, like the previously described systems, they can be massive by design and turn a very large box into a glacier and do some very serious cooling.

img7356In the past, the way around the "what do we do when we are not on board?" question was to put in a parallel AC or DC motor driving a redundant coil in the fitted holding plates. Yes, this created two independent and redundant systems, but it was very expensive. Essentially, there is unlimited (relatively) mechanical power available from the engine and no loss associated with an alternator and electrical generation, so it is very efficient. Engine-driven units, such as the Sea Frost 809, are used in most of the world's bareboat charter fleet because they are essentially bulletproof.

But while efficiency is very high, installations can be cumbersome and prone to wear from use. Also, an electric backup to maintain the box during periods of vacancy may be nearly as expensive as the main setup.

Weighing the options

OK. From what we have discussed, it should be apparent that the biggest variable/problem is dealing with those times spent not under way - and particularly not on board. The options available deal very nicely with needs from a simple cooler for weekending, to a major deep freeze for extended voyaging.

So we make these assumptions and suggestions:

1. That there has been an larger alternator installed as well as increased battery capacity.
2. The box insulation is at least 4 inches (preferably 6 inches) and is without significant voids.
3. The lids and or doors are properly insulated and gasketed.
4. Moving upwards in refrigeration power/capacity is not a problem and in fact recommended.

Vessels 30 to 40 feet: Air-cooled bin-type refrigeration will draw an average of 4 - 6 amps per hour, and in single box give a modest freezer capacity with the remainder of the box being refrigerator. If space allows, a separate freezer box (small) may be fitted with its own bin, and since it should not be opened very often, will cycle less frequently. You will have to purchase twice the equipment, but a true freezer can be had. On a 53-foot blue-water ketch, we had an engine-driven fridge and a 12V bin-type freezer. The freezer box was extremely well insulated, and the result was that we always had rock-hard ice cream! In fact, on one trip we lost the engine-driven fridge, but made ice in the freezer to keep the fridge box cool.

Vessels 40 to 50 feet: Now that we have more interior volume to deal with, a dedicated freezer is not unreasonable. So, too, is the prospect of having an even deeper sink of amp-hours in the battery bank with an appropriate charging system. At this juncture, we recommend again a DC system, either an air-cooled hermetically sealed unit or a custom water-cooled unit. At this point, however, a holding-plate system with its higher horsepower motor is in order to give longer periods between cycling. Even with the greater current draw, the holding plates will reduce cycling and even a 30-amp draw for two hours can be tolerated by a 400+-amp battery bank. Or, as suggested before, a timer to limit the total daily running time can be installed to keep things in check.

50 feet-plus: Now we are getting into a range where there will likely be little time when the boat will be left completely unattended - most likely a permanent crew will be on board. And more significant fridge and freezer box volumes can come into play with the extra interior galley space (consider, too, the freezer need not be located in the galley, but may be under a settee berth). When we get to this size, it is not uncommon to have a generator on board, so again power is not a consideration - assuming that the batteries will be topped up via the battery charger, when the genset is running, or via the alternator when the engine is running for propulsion. A 12V system is again recommended (appropriately sized) for the larger type vessel due to simplicity and the available power requirements aboard.

Some Blue Water thoughts: Clearly, the refrigeration dilemma is closely linked with the electricity dilemma. And since huge strides have been made in the areas of batteries and DC power production, it follows that a DC-driven refrigeration system will complement, rather than complicate, the entire mechanical system. Industry sources indicate a wane in sales and installations of engine-driven systems and two recent installations that we have made have been .5-horsepower DC motors driving holding plates. The result is an economical use of onboard resources and very happy customers. In this category, we like the Sea Frost 5000 and Glacier Bay Whisper Jet MK-11, as well as the more conventional belt-driven units from Crosby and Grunert.

On the simpler end, we do like the Technautics approach, which lends itself to owner installation (and owner understanding). Pre-charged system halves keep the techs out of the picture - at least initially - and minimizing mechanical joints by use of tested welded joints makes sense. If the installation requires that tubing be custom routed and cut, one of the more expensive units might make sense. But the newer pre-charged systems have merit. There are several units to look at in this category, and we would make our decision on ease of installation and price.

Consider this: if price is a deciding factor, you could install two $600 units and keep one on board as a spare! You may spend more amp-hours per day, but if you run the engine regularly, it may not be an issue. Remember to tailor your system around your habits and needs - all of the subtle improvements to gain fractions of amps may not be a significant as you think. I don't mean to belittle energy management and economy, but think practically about costs, usage and economy.

Regrigeration resources:

E.Z. Cold Manufacturing, Bloomfield, ON, Canada, phone: (613) 393-1122, fax: (613) 393-1130;

Fleming Marine Refrigeration, San Diego, CA, phone: (619) 222-9124, fax: (619) 222-9234;

Frigibar Industries, Inc., Miami, FL, phone: (305) 757-7697, fax: (305) 757-0252, Web: www. Frigibar.com;

Glacier Bay, San Mateo, CA, phone: (510) 437-9100, fax: (510) 437-9200, Web: www.glacierbay.com;

Great Water, Inc. (Isotherm), Erie, PA, phone: (814) 838-0786, fax: (814) 838-8700, Web: www.great_water.com;

Grunert Refrigeration (Marine Air Systems), Pompano Beach, FL, phone: (954) 973-2477, fax: (954) 979-2477, Web: www. Marineair.com;

Heat Shield Marine, Huntsville, AL, phone: (256) 830-2676, fax: (256) 830-2972, Web: www.htproducts.com;

Kenyon Marine (Adler/Barbour, Crosby), Clinton, CT, phone: (860) 664-4906, fax: (860) 664-4907, Web: www.kenyonmarine.com;

Mainstay Designs, Toms River, NJ, phone: (732) 255-1995;

Norcold, Sidney, OH, phone: (937) 497-3080;

Refrigeration Parts Solution (RPARTS), Berkeley, CA, phone: (800) 720-3907, fax: (510) 533-5605, E-mail: [email protected], Web: www.rparts.com;

Sea Frost, Barrington, NH, phone: (800) 435-6708, fax: (603) 868-1040, Web: www.seafrost.com;

Simpson Lawrence (Supercool), Imtra Corp., New Bedford, MA, phone: (508) 995-7000, fax: (508) 998-5359, E-mail: [email protected];