By what you run
Best marine inverter for a boat
Almost always the largest single load on the boat, and consistently the most underestimated, because the appliance is familiar and the current is not. A 1200 W kettle draws about 100 A at 12 V; twenty minutes of that is 33 Ah. Size the inverter for what you genuinely run at once, then size the bank for the inverter — and fit the cable and fusing it actually needs.
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Selection criteria and compatibility
- Continuous rating, not surge. The surge figure sells the unit; the continuous figure runs it.
- Pure sine wave, which is not optional on a boat with electronics aboard.
- Cable and fusing sized from the inverter's maximum DC current, which is larger than owners expect.
- A combined inverter-charger if you also need shore charging, to save a compartment and a set of cables.
The mistake to avoid
Sizing the bank before choosing the inverter
The inverter is usually the load that decides the bank. Pick it first, put its realistic daily duty into the calculator, and size the bank around the answer. Doing it the other way round is how people end up with a flat bank after making coffee.
The picks
Recommended options by application
Enough for a kettle or a laptop bench, and small enough that the cable run stays sane.
Where it falls short: You want to run an induction hob or a microwave and a kettle together.
Full detailThe middle size, marine-documented, and where most 38-footers end up.
Where it falls short: Your loads are a laptop and a phone — 1200 W would do it for less.
Full detailAn inverter and a shore charger in one box, which on a liveaboard saves a compartment and a set of cables.
Where it falls short: The boat is a weekender — this is several times the inverter it needs.
Full detailPure sine at well below the marine brands, for boats where 240 V is a convenience rather than a system.
Where it falls short: The install goes to survey, or you need a matched shore charger.
Full detailBefore you buy
Confirm battery capacity and equipment compatibility
A recommendation is only worth acting on once you know what the boat needs. The calculator works it out from your own loads in about a minute, and everything above reads differently afterwards.