Want to keep your sailboat's batteries charged without a generator or running the engine? A hydrogenerator might be the solution.
Sailors tend to use their engines far less than the average powerboater, and this creates an immediate problem of how to satisfy a boat's electrical needs. Lighting, electronics, refrigeration, and entertainment systems all require electricity to operate — all demands placed on the boat's battery bank. Solar panels, wind generators, and diesel generators have their place, but all have drawbacks.
I faced such a challenge many years ago on my first Atlantic crossing. We wondered how we were going to keep the batteries charged. By today's standards our electrical demands were modest, but we had no diesel generator. We calculated that we would need to run our main engine for two to three hours per day, a very inefficient and noisy way to charge the battery bank. Solar panels were rejected solely on cost, and there was no convenient place on the old ketch for a wind generator. Ultimately we settled for a "towed generator" — a small propeller at the end of a stiff line was trailed behind the boat, which turned a generator mounted on the back deck of the boat.
Modern iterations of the hydrogenerator are far more compact and easier to deploy. There are several manufacturers, but all use the same basic principle: they transform water flow energy into electricity using an alternator. Looking like a cross between a small outboard motor and a retractable rudder, modern systems are capable of putting out impressive amounts of power with minimum drag. In fact, all the boats in the last Vendée Globe race used hydrogenerators for producing all of their electrical energy needs. This made crucial weight savings by not requiring a heavy generator and the associated fuel tank.
In this video, you can watch one of the popular Watt and Sea units being towed behind a fairly modest sailboat. At 8 knots of boat speed in 14 knots of wind, the unit is putting out an impressive 16 amps of power. Price depends on which unit you choose, but expect to pay around $3,000 for a complete system.