Two years ago, my wife, Kathy, and I installed a wind generator on a 9-foot pole at the stern of our Tartan 34 sloop, Endeavour. We have used our wind generator in Florida, the Bahamas and the Caribbean, and we are pleased with what it has added to our electrical system.
Our battery capacity is 400 amp-hours, and we use about 110 amp-hours daily, primarily for refrigeration, single-sideband radios and lighting. In a seven-month season north of the trade-wind belt, the wind generator saves possibly 60 hours of diesel charging, assuming 1 1/2 hours of battery charging each day. In Caribbean trade-wind latitudes, the wind blows 20 to 25 knots a lot of the time, particularly in the winter. In the trades, the wind generator can save 90 hours of diesel operation in a seven-month period.
Given our half-gallon-per-hour diesel consumption when powering our 135-amp alternator, the $1,000 wind generator probably isn’t very cost effective. But like most wind generator owners, we simply don’t care; we like the “free” wind power. Besides, the wind generator needs very little maintenance.
We shut the generator down 1) in less-than-optimum wind conditions, 2) when the 400-amp-hour battery bank has reached a full charge, or 3) when motoring. It’s possible to run the generator when sailing, but most often, we let our 64-watt solar panel provide power. When sailing at night, when there is no solar input, we usually run the wind generator.
Given that most manufacturers limit output at high winds or when batteries are fully charged, it would seem okay to let the generator continue to spin at all times, even when it isn’t contributing to the boat’s electrical system. The problem is that if the unit is still spinning, it is causing bearing wear. Plus, the blades continue to become contaminated with salt. Solar panels can be left unattended for months at a time, whereas wind generators perform better and last longer when attended.
In up to 10 knots of wind, most wind generators provide negligible output and might as well be shut down. At 25 to 30 knots of wind, the output reaches 25 to 30 amps, or more, of electric current. Most wind generators are designed to limit output above 30 knots of wind to slow mechanical wear and tear, limit noise and to limit electric current. Each manufacturer has its own means to limit speed, output and noise. Some feather the blades, others use a blade clutch, some even require stalling the generator (by turning it away from the wind) and tying down the blades. The Air Marine 403 generator blades are designed to stall at 25 to 30 knots of wind. The newer Air-X generator can brake blade rotation electrically at high wind speeds.
Many wind generators are located high in the rigging and are generally inaccessible, particularly during high winds, and operate unattended. Our experience is that when the wind blows at 25 to 30 knots (producing 25 to 30 DC amps), it will likely blow hard for several days. Likewise, when winds are light, they are light for several days. What this means is that 24 hours of 25-knot winds will top off our 400-amp-hour battery bank. After a day or two of strong winds, we frequently shut down the wind generator, particularly at night.
We have noticed that the wind generator does cause drag on the boat, especially at high wind speeds. This is reasonable, since we are taking energy out of the air. The Air Marine 403 produces about 793 watts of electric power at 25 knots of wind.
Shutting down the wind generator
Air Marine, like many wind generator manufacturers, allows the output of its unit to be shorted electrically, without damage, as a means to shut the unit down. We frequently shut it down by electrically shorting the output when the batteries are fully charged or when we want maximum quiet in high winds, particularly at night.
When shorted, the generator blades turn slowly in the high winds. To short the generator output, a single-pole single-throw automotive 30-amp, 12-volt DC relay was installed in the generator output circuit. A single-pole single-throw switch, located at the navigation station, controls the relay. In the normally closed, or “off,” position, the generator output leads are shorted: generator positive to generator negative. In the “on” position, the switch energizes the relay and connects the generator positive directly to the battery bank. When we have had enough of the wind generator, or wish to service it, we simply switch it off. A 50-amp circuit breaker or switch can be used rather than a relay. Because the entire battery bank is connected to the “normally open” pole, a relay is safer against an accidental dead short than a 50-amp circuit breaker or a single-pole single-throw switch. To guard against shorts, a 30-amp automotive fuse was installed in the wind generator circuit.
Since noise results from blade rotation in the moving air stream, like an airplane propeller, wind generators are inherently noisy if they are to produce increasing amounts of electric energy at increasing wind speeds. At low and moderate wind speeds, all are reasonably quiet, whereas they all make noise as they approach their stall speed. Some are quieter than others, depending on design. One way to limit noise, particularly when trying to sleep at night, is to be able to shut the generator down electrically from inside the boat. Not only does this limit noise, it reduces mechanical wear and tear on the unit.
Cleaning and storing
Many wind generator installations are located high in the rigging or on the mizzenmast. These types of installations can make the wind generator difficult to service. Wind generator output can be limited severely when the blades are coated with salt. In some locations, air heavy with salt can coat the blades in just a few days. By design, our wind generator blades are reachable by standing on the stern rail (see picture). When the output is lower than normal, or when we can see salt deposits on the blades, we clean each blade using soap and water. The blades are removed from the generator body when the boat is stored for more than a month.
Dick de Grasse is an engineer and holds a U.S. Coast Guard masters license.