Some real-world data points:
My O'Day 25 had a small icebox (about 2.5 cubic feet), rather poorly insulated, with a small Isotherm refregeration system. The unit drew about 4 amps when running and ran about 1/3 of the time in hot summer weather. Energy used was about 8 hours x 4 amps = 32 amp hours.
My Island Packet 38 has a large icebox (14 cubic feet) with medium to poor insulation. My Adler-Barbor cold machine uses 6.5 amps when running and runs about 2/3 of the time when the outside weather is 80 degrees +/-. Energy used is 18 hours x 6.5 amps or about 117 amp hours. Clearly, I need better insulation. :-)
How about some other data points?
Jeff
www.smartcaptain.com