ProjMan, If you were satisfied with performance of old refrigeration system’s performance why not repair it yourself? Most of the time problems are simple to repair without a serviceman.
In 1980 thirty ft production sailboat iceboxes were not intended to be converted to refrigerators operated at box temperatures below 50 degrees F. The problems with these older production boat boxes and even many newer boat boxes is their designs do not address air infiltration leaks, most have less than adequate insulation needed for operating in warm climates, and on these boats their electrical power grids will not support refrigeration.
There are five things you must consider when making your decision about refrigeration:
1. What size refrigerator do you require?
2. What temperature do you require inside refrigerator?
3. How will water and air ambient temperatures where you plan to cruise affect your refrigeration system’s performance?
4. Will your final system have adequate insulation?
5. Final point, will be, is electrical power grid adequate for refrigeration?
My thoughts on a portable 12 volt refrigeration unit like the Engel 45 quart system for your application. I am sure there are other units equal to this unit but I have only tested the Engel under controlled conditions.
1. Engel forty five quarts capacity has about 1 ½ cubic feet of refrigerated space.
2. Engel’s thermostat can be set anywhere from a +47 degree, a drink cooler, consuming 10.8 amp-hrs a day to a – 2.65 degree freezer consuming 57 amp-hrs a day, both tests were on a 24 hour 80 degree ambient air temp testing period.
3. Power consumption of mobile refrigeration will increase 4% per degree when air temp is above 80 degrees and will decrease by 2% per degree temperature below 80 F degrees.
4. Engel `45 has good high density insulation and only a 4 degree across insulation heat loss at zero degrees box temp.
5. It is possible to live with 200 amp-hr battery bank when consuming less than 50 amp-hrs per day for refrigeration but for your planed use of boat I would recommend at least adding solar panel of 80 watts or more. Solar power will increase life of batteries and greatly reduce daily engine running time.