Designing a custom refrigeration or freezer system requires professional expertise, since a qualified technician needs to determine the cubic feet of space you need to cool and what insulation requirements to consider. These numbers determine the necessary BTUs and load rating required by the compressor. Don't guess on these numbers if you want your box to chill correctly.

If you need extra cooling capacity, you can add refrigeration just about anywhere as long as you can provide adequate insulation, and can get to the box and lines carrying the refrigerant. This ability to customize opens up a lot of possibilities for boats that didn't come with a half-dozen built-in freezers. Of course, you must also make room for the compressor and condenser, but these also come in smaller combo units to use when space is tight.
 
If room is scarce, and you don't want to go to a bunch of trouble and expense, you can always try a Frigid Rigid stand-alone freezer. These heavy-duty versions of the renowned Frigid Rigid coolers come with an extra inch of insulation, providing 3 inches of polyurethane foam insulation encased in a tough fiberglass shell. You can use a Frigid Rigid as a freezer or refrigerator just by adjusting the temperature dial. These units use a continuous copper coil built right into the cooler instead of chill plates and come in 115- or 12-volt versions. They also make great traveling dock freezers.
 
While all of these devices are obviously useful, I think the Eskimo Ice Machine represents the best invention in marine cooling ever! Inventor Bill Grayson's raw-water cooled machine converts the boat's fresh water supply into crushed ice, and then transports that ice through a commonly available hosing to wherever you want it. How cool is that (pun intended)?
 
Fish stay the freshest when surrounded by crushed ice, and the Eskimo Ice 600 makes 25 pounds of ice per hour when raw water temperatures average at least 75 degrees. The compact ice machine weighs only 140 pounds and is about the same size as many CruisAir air-conditioning systems. Ironically, Grayson sold the Eskimo technology to the Dometic Environmental Corporation, the makers of CruisAir ACs and Sentry battery charging systems, so I guess it's no wonder they look so much alike.
 
I first saw an Eskimo machine aboard a charter boat run by Capt. Allan Starr many years ago in Isla-morada. He and I both stood and marveled for some time at the crushed ice oozing out from a small hole in the side of the fish box. It simply amazed us.
 
But it wasn't until many years later that I learned the true value of the Eskimo machine. After a long day of sailfishing aboard the 58-foot Merritt, Briar Patch, in Isla Mujeres, Mexico, Capt. Karl Anderson scooped up several cups of clean crushed ice from the fish box and filled them with a 50-50 mixture of fresh-squeezed orange juice and Bacardi Añejo. Only then did I truly appreciate the wonder of modern refrigeration technology.