Heading offshore in a buddy's battlewagon with summer at full strength, we found ourselves gravitating toward the enclosed flybridge, where the blast of cool air conditioning felt like a godsend. It's a great perk to have on a boat, but you can't run the A/C unless you have, well, AC. As in alternating current, or 120-volt AC power.
The question is, while offshore, how are you going to get it? That depends on what's on your boat and how you use it.
Cool Runnings
"What requires AC power are heating and cooling devices," says Gino Kennedy, who has over 30 years of marine generator experience and is the owner of Next Generation Power Engineering in Jacksonville, Florida. "Such as when you have a microwave, a coffee maker or air conditioning."
You can deliver AC power on your boat in two ways: from a generator that converts fuel to electricity or from an inverter that turns 12-volt DC (direct current) juice from your batteries into 120-volt AC. An inverter can handle some load, but not much.
"Once you want to run air conditioning, you need a generator," says Kennedy. Even with no air conditioning on a boat, running high-capacity hot water heaters, electric heating, an electric galley, a large refrigerator or an entertainment system could create the need. The rule is once you have 120-volt components that require, in total, between 1½ and 2 kW to run, it's generator time.
Why? "Battery power is in the Stone Age," says Kennedy. They're heavy for the power provided, and to get enough juice you'd need at least $5,000 to $10,000 worth of batteries that would add serious weight to your boat — the preferred 8D batteries weigh about 125 pounds apiece, so a generator makes more sense.
Small-Block Electric
There's an easy way to estimate what size generator you'd need on your boat. Add up the watts listed on the 120-volt appliances you want to run offshore. (A microwave and a coffee maker typically draw over 1 kW.) If you see only amps listed, convert to watts with this formula: watts = volts x amps. Pick a generator that will meet your needs at about two-thirds of its output rating.
What's it going to cost? A 42-foot boat with a single air-conditioning unit would typically need a 3 to 5 kW generator, which would cost between $5,000 and $8,000. Installation costs depend on whether your engine room is set up for a generator option.
Do you have to install another fuel tank or plumb your existing one? Do you need to add an AC panel? A shore-to-generator power switch? Do you add a dedicated starter battery? Expect to pay anywhere between $1,000 to $3,000 for the installation.
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