2 .House-style, front-opening electric
refrigerators and freezers. These
are usually powered with 120 volts
AC but may be powered to run off
12 volts DC instead of or in addition to
120 volts.
3 .Icebox conversions.This is a bit of
a misnomer, as many of these are
designed to fit in purpose-built
insulated boxes to form refrigerators.
These systems can be thought of as the
mechanical “guts” of standard fridges.
They may run off 12 or 24 volts DC,
120 volts AC, a compressor clutched
directly from the main engine, or some
combination of these.
4 .Holding-plate or eutectic-plate
systems.These also fall under the so-
called icebox-conversion category;
however, they may be the most effi-
cient refrigeration available for boats.
They may run off 12 or 24 volts DC,
120 volts AC, a compressor clutched
directly from the main engine, or
some combination of these.Portable coolers and freezers are suited
to day boats and as extra refrigeration capac-
ity for, say, big parties on larger vessels. The
only requirements are a place to stow them
properly and a proper electric connection
with suitable power.
House-style, front-opening electric
refrigerator/freezers are commonly used on
small to midsize powerboats. Their advan-
tage is that they function just like the fridge
in your home. They are not particularly
efficient compared with built-in fridges, how-
ever. These self-contained, front-opening
units have only modest insulation, and their
large, front-opening doors spill out much of
the cold air every time they are opened. Also,
the boat needs lots of electric power to run
these units. A cruising powerboat runs these
off 120 volts AC at the dock or when the gen-
erator is running. Many of these units have a
built-in inverter to allow them to run off DC
power under way. Alternatively, you can get a
true household unit and run it off the batter-
ies through the shipboard inverter. Both
work acceptably. (Note that units with built-
in inverters should not be run off shipboard
AC from the boat’s inverter.)
Another drawback to a front-opening
door is that the unit can dump much of its
contents if opened in rough weather. I re-
member spending more than 20 minutes
crawling around the saloon floor of one of my
office’s motor cruisers, collecting all the stuff
that sprang out when someone opened the
fridge in a 50-knot storm. Not my favorite
way to get exercise, though an excellent way
to sharpen reflexes!
Because of their easy availability and
familiarity, it’s becoming increasingly common
to find household-type refrigerator/freezers
installed on quite large boats. Though they are
acceptable, I recommend custom, built-in
refrigerators and freezers, run off cold plates—
at least as the primary refrigeration. Not only is
this more efficient, but these built-in units can
have much greater volume to store the large
amounts of food such sizable vessels need.
Icebox conversions are ideal for small
sailboats. Because sailboats run their engines
so infrequently and often don’t have a gener-
ator, maximizing refrigeration efficiency is
paramount. Top-opening fridge compart-
ments are built in with 3 to 6 inches (75 to 150
mm) of foam insulation. The thick insulation
and top opening retain the cold air much bet-
ter than a household-style front-opening
fridge. Still, these units may cycle on and off
about 30 percent of the time.
Holding-plate or eutectic-plate systems
operate the same way as any other refrigera-
tion (Figure 15-5), but they freeze a thin box
(the plate) filled with the eutectic solution of
an easily melted material that has a freezing
point lower than water. The frozen eutectic
plate “holds” the cold for several hours. In a
well-insulated box, proper temperatures can
be maintained with only a couple of hours of
compressor operation per day.Powering Icebox Conversions
and Holding-Plate Systems
Both the so-called icebox conversions and
the holding-plate systems can be powered
off 12 or 24 volts DC or 120 volts AC. Alter-
natively, their compressor may be clutched
right off the main engine. The direct-engine-
driven compressor is the most efficient, as
there is no loss in converting engine powerChapter 15: Air-Conditioning and Heating