Running Marine Air Conditioning at Anchor
The short answer
Three routes: a generator, a large lithium bank with an inverter, or a 12 V DC unit that skips the inverter entirely. All three are a real investment. A 16,000 BTU system pulls about 1.56 kW, so a night of cooling is roughly 9–11 kWh once you allow for the duty cycle.
Running Boat AC at Anchor — Requirements and Limitations
That number is the whole conversation. Nine kilowatt-hours is a serious lithium bank — well beyond what most cruising boats carry for everything else — and it has to be put back the next day by solar, the alternator or a generator.
The variable-speed DC units change the arithmetic because they throttle rather than cycle and have no inverter losses, but they cost more per BTU. Fitting air conditioning you can only run at a marina, on a boat that rarely visits one, is the common and expensive mistake.
Related Sizing, Installation and Service Guides
Each of these answers a different part of the same problem.
- work out your own nightthe calculator, with bank size and source
- the DC unitsthe route that avoids the inverter
- the short answerif you want it in a paragraph
- what each route costsshore power, generator and battery compared