A boat icebox (or refrigerator) with enough insulation has never been built. Nor will it ever be built. Ice will always melt. Fortunately, it doesn't have to melt as fast as occurs in the typical boat icebox. The minimal amount of insulation provided by the original builder can be increased enough to double the life of a five pound block of ice.

Efforts at prolonging the life of ice involve using gaskets and insulation to prevent warm outside air from penetrating into the icebox. Efficient gaskets are probably more critical than thick insulation. Look at kitchen refrigerators. Great attention is paid to providing a flexible gasket between the door and surrounding box. This gasket is usually magnetic so it will stick tightly to the metal of the outside box. Compare that to boat iceboxes where the top-loading hatches seldom (if ever) have even a rudimentary gasket.

Home Made Gasket

Self-stick rubber weather stripping available at regular hardware stores is an easy way to improvise the hatch gasket forgotten by the builder. Purchase the more expensive closed cell foam weather stripping instead of the less costly open cell foam. Closed cell foam doesn't soak up water and it tends to last longer. A bit of imagination may be necessary to install the foam tape so that the hatch still closes flush with the counter top.

Insulating Top-Loading Hatches

Surprisingly, the top-loading hatch of the icebox may not be insulated. Many have a beautiful plastic thickness piece that gives the illusion of several inches of insulation. Inside the plastic, however, there is nothing ... just empty space. Filling this empty space with real insulation improves the icebox's ability to keep ice. Aerosol spray foam insulation sold in cans by hardware stores to seal cracks in home foundations works well for this purpose

Drill a small hole in the hatch to allow the foam to be squirted into the hollow space of the thickness piece. Use the applicator straw supplied with the can to direct foam to the farthest recesses of the hatch. (Large hatches or those with unusual shapes may require two or more filler holes.) Let the foam effervesce out of the hole. Once it has hardened, trim the foam back inside the hole with a sharp knife. Then fill the hole with Marine-Tex epoxy putty sanded smooth.

Side Insulation

Most boats have empty spaces between the hull and the sides or bottom of the icebox. Small spaces of this type are also good candidates for aerosol spray foam. Larger spaces require 2-part pouring foam which comes in two parts which are mixed together into a milky liquid which is poured into the space to be filled. Almost immediately a chemical reaction begins. Gas bubbles turn the liquid into a frothy foam which fills the space with a great rush. Because of the gas generated during the "blowing" process, all work must be done in a well-ventilated area.

Build temporary dams of plywood covered with vinyl sheeting to keep the foam where it's needed. These dams must be well braced. Expanding foam exerts an unexpected amount of pressure on its container. Always give the foam an escape route, usually out the top. Excess foam can be trimmed away with a hand saw or sharp knife after it hardens.

Styrofoam planks sold by lumber yards as building insulation are an excellent and inexpensive alternative to pouring foam. Planks can be glued to the outside of existing insulation around the icebox to make it thicker. Most boxes start out with a thin blanket of factory-installed styrofoam. Additional layers can be glued over top with latex construction cement. Latex cement must be used because conventional construction cement will melt right through styrofoam.

Cut the planks to size and dry fit everything before opening the cement. Number the pieces for easy re-assembly. Small nails can be used to "pin" the planks in position during dry fitting. They will also hold everything in position while the cement cures. Just stick them through the styrofoam like pins into a cork board. Remove these nails once the cement sets to keep them out of the bilge.

Pro Tip: Beat The Heat

Two-part foam has some unusual handling characteristics. It pays to mix small batches until familiar with the product and the procedures. Never work on a hot day as heat speeds up the chemical reaction. With some products it is possible to slow down the blowing process by refrigerating one of the components for 24 hours before use. Conversely, using room temperature foam on a hot summer day can result in an almost explosive reaction.