I've noticed several requests for A/C information (on other forums) - so here's a little basic information on Marine Air-Conditioning:
A-C Cooling Pumps:
Centrifugal type water
pumps offer several advantages over positive-displacement types. They typically run quieter, longer and consume less power. Unfortunately, centrifugal pumps are not very forgiving when it comes to poor installations ~ they will NOT run ‘dry’ (check & clean filtres often). If you are installing one of these pumps make sure you understand what is required to ensure a good self-priming installation
The sea water
requirements for cooling Marine
is about 200 gallons/hour (3.33 gpm) per ton of air conditioning(12,000BTUs= one ton) at a maximum ambient temperature of 100̊F.
In the ideal installation
, the cooling water enters the vessel via it's own through-hull located deep on the hull
. The incoming water then rises to the sea strainer and continues smoothly uphill to the inlet of the water pump (The through-hull, sea strainer and pump are positioned so as to remain under the water line and continue this uphill sloping attitude at all angles of heel). The discharge outlet of the pump points upwards with the connecting hose continuing to rise smoothly into the Condenser Unit inlet. From the Condenser Unit outlet, the connecting hose then continues to a discharge through-hull located above the water line and above the level of the water pump.
Sizing Marine Air-Conditioning (BTU's Needed)
Two “Rules of Thumb”:
: 14 BTUH/Cu Ft
Length x Width x 6' average height x 14 BTU
10' x 7' = 70 sq.ft.
70 sq.ft. x 6' = 420 cu.ft.
420 cu.ft. x 14 BTU = 5880 B.T.U. + 1000 BTU
Topside (area above main deck): 17 BTUH/Cu Ft
Length x width x 7' average height x 17 BTU
18' x 11' = 198 sq.ft.
198 sq.ft. x 7' = 1386 sq.ft. 1386 x 17 B.T.U. = 23,562 BTU + 1000 BTU
“How to Select Air-Conditioning for Your Boat” http://www.marineair.com/customizer/
“DIY Air-Conditioning” (Practical Sailor)
Use the chart below to estimate the total 24 hour heat load experienced by a couple living aboard
in a tropical climate. First, measure your box to determine it's interior surface area
(including partition dividers) in square feet. Then multiply it by the numbers below.
HEAT INFLUX PER 24 HRS., PER SQ. FT. OF INTERIOR
BOX SURFACE AREA
"R" Value 
(Insulation Thickness) - Refridgerator Box - Freezer
R10 (2") - Fridge 150 BTUs - Freezer
R15 (3") - 120 BTUs - 225 BTUs
R20 (4") - 100 BTUs - 185 BTUs
R25 (5") - 90 BTUs - 170 BTUs
R30 (6") - 80 BTUs - 160 BTUs
[*1] While some authorities prefer to estimate heat load based on the volume (ie. cubic feet) of the ice box, others have found it more accurate to make the calculation based on the interior surface area. This method better estimates the additional heat load which occurs when an odd box size gives reduced volume but a large surface area.
[*2] The performance given is based on the typical "R" value for good quality polyurethane foam board. Two-part "pour-in" foam and wet foam of any kind will have a lower insulation value.
The very best website I’ve ever seen for Marine Refrigeration is Richard Kollmans’s sites at: