The icebox of almost any production boat can be made to do for most uses, but when it comes time to consider mechanical refrigeration, or if you simply want a very efficient cold box, it may require radical surgery. The fact is that few iceboxes, will be adequate for the addition of refrigeration if engine running and electrical demand are to be kept to a reasonable level.

For example, 12 volt sealed compressor refrigeration systems, such as the ColdMachine or Nova Kool, draw about 5 1/2 amps when running. The refrigeration manufacturer may claim an average current consumption of two ampere hours, assuming that the system will only run about 20 minutes out of every hour.

That assumption, unfortunately, is predicated on a reasonably efficient box. A close look at Nova Kool's literature reveals that running the unit 20 minutes out of every hour assumes a box with 2" to 4" of polyurethane insulation. Few standard iceboxes aboard production boats have that much insulation, and the configuration of many boats makes it difficult or impossible to add enough insulation to get the box up to these standards.

What it means to you is that while you're out cruising, you'll have to run the main engine or auxiliary generator at least an hour a day just to keep your beer and soda cold.

There are several solutions to the dilemma, none cheap or easy. You can add another battery and a bigger alternator. You can always tie up to the dock, so you can run the thing off shore power. Or you can totally rebuild the box to make it suitable.

Removing an existing icebox is not to be taken lightly. It can as easily decrease the value of your boat as increase it. If the galley becomes more crowded, and you happen to be trying to sell your boat to someone who doesn't really care if it holds ice for a week, the time consuming and ex- pensive improvement you've wrought may be for nothing.

In addition, if you do a job that looks bad, you may have gone to a lot of trouble for zero net gain.

If, on the other hand, you plan to keep your boat a few years, you are capable of handling power hand tools, fiberglass, paint, and mica laminates, a custom icebox built from scratch can go a long way toward dramatically im- proving the livability and usefulness of your boat.

Don't think this is an easy job. Building a proper icebox may be the most complicated systems improvement you ever consider, aside from changing the engine installation. On a custom 55-footer we recently examined, the icebox, which was a freestanding console in the middle of the main cabin, cost over $4000. And it wasn't much larger than that found on a good 40' cruising boat.

Unless you're building a boat or completely remodeling the interior of an existing boat, the location of the new icebox will be determined by the placement of the old box. This may place you at a severe disadvantage, for production builders frequently position iceboxes right next to the engine compartment - frequently the hottest location on the boat.

Another popular location is under the main companion- way, where the sun beats down on the top of the box during the middle of the day.

If you want to rebuild an icebox that suffers from poor location, design extra insulation on the surfaces exposed to greater heat. Unless there is room to increase the outside dimensions of the box, rebuilding with better insulation may well require a loss of some inside volume.

As a rule, the loss of interior volume is not a matter of major concern. A box of about seven cubic feet is more than adequate for a boat cruising with four people. Bigger boxes mean more volume to be cooled, and more surface to be insulated.

The degree of complication in building a box from scratch depends very much on the internal construction of the boat. If the boat has molded galley furniture which contains the icebox, you should think twice before destroying the outside box structure.

It may be contributing to the internal stiffening of the hull.

If, on the other hand, the galley furniture is built up out of solid wood or plywood - as it is likely to be on a custom boat or if you are building a new boat - you have much more flexibility.

It is very important that the new box fit in with the existing interior decor of the boat. Use mica laminates over plywood to replicate molded fiberglass furniture, for example, or wood veneers or solid lumber in a wood interior.

In designing an icebox, there are several ergonomic considerations that are frequently overlooked by production builders which you may be able to correct:

. kick space whenever possible, there should be a toe space under the face of the box at least 3" deep, so that it is possible to get closer to the counter. This space need be no more than about 6" high;

. inside depth should be limited to what the cook can comfortably reach without standing on his or her head;

the lid should be no larger than necessary to get the largest block of ice in and to provide access to the interior.

Do not, in an effort to ease access, install a front- opening door on an icebox. Although it may be easier to reach the interior, it is also too easy for cold to get out every time the box is open. Aboard a sailboat, front- opening boxes also tend to spill their contents in a seaway.

Basic design

The easiest box to build is a freestanding, rectangular shape that doesn't have to conform to the sides of the hull. Most people are more comfortable working with right angles than with the compound curves required when fit- ting a box to the hull side.

Ideally, the box should be no higher than the surrounding counters, for ease of access. A counter height of 33" to 36" above the cabin sole is about right. Be sure that there is adequate clearance above the top of the icebox - about 18" minimum - to make it. possible to fully raise the lid and get things in and out.

The depth from the front of the counter to the inside back of the box should not exceed about 24", less if there is no kick-space to allow you to get closer to the front of the box. this requirement can be ignored if there is access to the box from all sides. If there is any doubt about the dimensions, mock up the box with cardboard or thin plywood to check accessibility.

It is important to consider how the weight of the box will affect the boat's trim. If you're replacing an existing icebox, weigh the material you remove from the old box, and weigh the pieces of the new one. A heavy box tucked under the side deck, away from the boat's centerline, can significantly alter trim.

A surprising number of production boats have substantial list as they come from the builder, the result of im- proper placement of heavy weights. You can easily determine the amount of list a boat has by taking free-boards amidships on both sides of the boat.

On a calm day, with the boat loaded as it usually is for sailing, measure the vertical distance from the deck, bottom of the toe-rail, bottom of the rubbing strake, or some other reference to the surface of the water with a folding stick ruler. Measure from a dinghy, with no one aboard the boat.

You may be surprised to find how out of kilter the boat is. A difference of less than 1/2" between the two sides of the boat at its widest point is insignificant. Any greater variation means you should change stowage habits or relocate heavy items of gear such as tanks, icebox, or batteries.

The depth of the box is another consideration. Although the first food shelf may be well above the bottom of the box when ice is used, cans and bottles usually find their way to the bottom pretty quickly. An inside depth of much more than 24" will be a long reach for a short person.

Probably the best shape of all for the cool box is a long, narrow, shallow, rectangular box. There will be less temperature differential between the top and bottom of this shape, and the ice can be distributed over a larger bottom area. The space underneath can be compartmentalized for pan storage, which always seems to be in short supply. Unfortunately, few boats have the counter space to sacrifice for this configuration.


The easiest and best material to use for insulation is sheet polyurethane foam, available at building supply outlets. This board comes in various thicknesses, and costs about $14 per inch of thickness in a 4' x 8' sheet. There are two basic approaches to insulating a new box. You can build the outer shell of the box, including the bottom, line this shell with insulation, and then install a liner. Or you can build the liner, insulate the outside of the liner, and drop it in the outer shell. Usually, the outer shell is insulated, and then the liner is added.

The outer shell is built first, including the bottom. As much as possible, the support framing for the box is outside the shell, but hidden by adjacent joiner-work. This is done to minimize the amount of insulation lost by working around internal framework.

Before installing the insulation in the shell, a vapor barrier should be fitted between the shell and the insulation. Mylar/foil Space Blanket material, available at sporting goods stores, makes a good vapor barrier. It can be taped to the shell with duct tape. Be careful to seal all the joints in the vapor barrier.

The minimum thickness of insulation on all surfaces is 2", but if the boat is to be used in the tropics, or fitted with refrigeration, 3" to 4" should be used. It is especially important to maximize insulation on surfaces that face unusual heat, such as near the galley stove or engine box:

Urethane foam cuts easily with a sharp knife or saw. Be careful in handling it, as it is brittle and tends to crumble easily if abraded.

All comer joints should be step lapped rather than butted or mitered. If you use 1" thick panels, the step lap can be created by fitting the side and end panels first, then the bottom panel. The fitting sequence for the next layer is ends, sides, bottom. If a third or fourth layer of insulation if fitted, just repeat the fitting sequence. Do not permanently install the insulation yet.


One advantage of urethane foam is that it is not attacked by styrene, so that a fiberglass/polyester liner can be laid up directly on the foam. If at all possible, do not try to do this step with the insulation in place, as it will require glassing to vertical panels, then grinding smooth and finishing. This is a nasty job.

Instead, after all the insulation for the sides, end, and bottom of the box is fitted, use a marker to indicate the in- side dimensions of the box, then number the pieces of insulation and remove the innermost layer from the box. Cut several layers of light fiberglass cloth to the size and shape of the exposed inner surface of the individual pieces of insulation. You only want to glass up to the lines you marked on the insulation before removing it from the shell, rather than the entire surface of each piece.

Three layers of light fiberglass cloth will make a reasonably sturdy liner that will allow you to tap into it for supports for the shclves to be installed in the box later. Be as neat as possible in your fiber-glassing to minimize the amount of f1nishing work required. The liner should be as smooth as possible to facilitate cleaning.

If you are considering adding refrigeration at some time, you should make a liner of 1/4" plywood to which the glass is applied, rather than glassing directly to the insulation. This will allow you to fasten heavy holding plates to the inside of the box without fear of the fastenings pulling out.

Whether you glass directly to the insulation or build a plywood liner, the comer joints will have to be taped with fiberglass after the insulation panels are reinstalled in the box.

Reinstall the insulation in the shell. Layers of insulation can be glued together with contact cement, silicone caulk, or polysulfide. All comer joints should be caulked with silicone or polysulfide. If a fiberglass-over-plywood liner is built, it can be attached to the inner layer of insulation with polyester epoxy, or one of the caulking compounds.

If you're really clever, you figured out where the drain will have to be installed in the bottom, then ground a small recess in the bottom insulation at this point so that the drain fitting can be installed flush with the bottom surface later on. If not, don't worry, it just means that you'll have to mop the last little bit of water out of the box with a sponge.

With the insulation and liner in place, the inside comer joints are glassed and the entire interior given a coat of clear resin. The last bit of sanding to smooth out the taped comer joints should be done before applying the final coat of resin.

Wax-free polyester resin should be used for the liner lay-up. This remains slightly tacky to the touch, but it means that it doesn't have to be sanded between coats of resin. In addition, the polyurethane or epoxy paint that you use to finish off the inside of the box will adhere better. We don't recommend trying to gelcoot the inside of the box.

The Top

At this point, you have a nicely insulated shell with no counter or lid. If your boat has mica-laminate counters, the top of the box can be made of plywood with matching laminate applied.

Another option is the use of maple butcher block, which is extremely heavy, but very attractive and not as expensive as you might think. The piece of block used for the icebox here was custom made by Eastern Butcher Block, a New England chain, and cost about $65. If you use butcher block, it must be ordered unfinished. The standard clear vinyl finish which is factory applied makes it look like a mica laminate, and an oil finish is too water-permeable for use aboard a boat. A polyurethane varnish coating is best.

The opening lid to the icebox is a key detail. It must be as well insulated as the rest of the box, and should be gasketed. If the boat is intended for offshore sailing, the lid should be hinged and equipped with a latch, to keep things in place in case of a serious knockdown.

For less arduous types of sailing, a simple unhinged lid which lifts out can be used.

Insulation and lining for the top can be constructed in much the same way as the rest of the box, with one exception. The best way to make the joint between the lifting lid and the rest of the top is to finish both the edges of the lifting lid and the top with solid teak. These can be match- bevelled or step-lapped to form the joint the lifting lid will rest in, on the side opposite the hinge. If the lid is hinged, a bevel must be usce which is radiussed to the arc the lid will swing in when opened. Now you see why a drop-in lid is less complicated.

The insulation is fitted to the underside of the counter by trial and error, then the counter screwed down on the rest of the box. Once again, use caulking in the joint between the box insulation and the counter insulation. It will probably not be possible to glass this joint on the inside, but a good caulking job will suffice to provide an adequate seal. Remember to paint the inside of the box before in- stalling the top, because it's no fun to try to get your head inside the opening lid to do the job. At every step along the way, stop and think before doing anything irreversibe, as the sequence of construction is critical.

For example, it is much easier to install the interior shelves and their runners before the top is permanently installed. Simple teak cleats with a one inch square cross section, screwed to the fiberglass liner with self-tapping screws, make perfectly good shelf supports. Shelves can be made from thick acrylic, plywood, or even molded from fiberglass.

If the top is plywood, install the mica laminate after the top is fastened down. If it is butcher block, counterbore into the top from the upper surface, then plug the screw holes with bungs cut from scrap maple to finish off.


Now you see why few boatbuilders build good iceboxes. They are incredibly labor intensive, and once in place, it's not easy to tell a good box from a lousy one, except by using it.

As with most major projects of interior alteration almost as much time is spent in planning as in execution. The advantage of spending the time planning, however, is that numerous versions of the project can be tested on paper before picking up the first tool.

For anyone contemplating living aboard or cruising for more than a week at a time, a good icebox is one of the things that makes the difference between camping out and truly "living" on a boat. Frankly, if we wanted to, camp out, we'd go to the moutains. We'll take comfort with our cruising.