I was looking over Mermaid's product line and found this copy on their smallest AC.
M5: 5,200 BTU Cabin Air Conditioner
Smallest footprint on the market and weighs in at 31.5 lbs. for the unit, and 4.7 lbs for the electrical box! This unit has a rotatable blower and tapers down to a "V" shape for those odd angle discharge installations. We use 4" ducting and recommend a minimum of 2, 4" round supply grills with this installation.
This unit will run off the new Honda eu1000i 1,000 watt portable generator, while in cool mode. Another option is to use a Statpower 1,800 watt inverter and 450+ amp hours of battery power and you can anchor out (one average) for one night. We have actually had success operating the Mermaid Model M5 off as low as a 1000 Watt Inverter and only 400 amp hours of battery power, however, longer operating times, it is recommended to use a higher wattage inverter and a bit more battery power.
On average, this unit is designed to cool cruisers up to 26' and sailboats up to 28'. All M5 models include a programmable digital thermostat. Pump Not Included.
5,200 BTU Cabin Air Conditioner Specifications
Cool = 4.4 amps, R/C = 5.5 amps.
Add approximately one amp for the standard seawater pumps.
Start up amperage is calculated by running amperage multiplied by 1.8.
COOL ONLY UNIT: L-15" W-11.5" H-11.5
REVERSE CYCLE UNIT: L-18" W-12" H-11.5"
This is from their master distributor: