Catch the Wind

Wind generators offer boatowners a free, unlimited source of energy to power all those onboard necessities. Here’s how they work.      

By Frank Lanier

Chesapeake Bay Magazine (2003)

            To find where my respect for wind power was born, I need look no further than a childhood spent on the hurricane-prone coast of North Carolina. From howling storms to the benign breezes that propel our boats, free, unlimited energy is obviously out there. The trick is harnessing and harvesting it—and that’s exactly what wind generators let us do. The ever-increasing power needs of today’s onboard electrical systems are matched only by the challenge of keeping the batteries charged, so who wouldn’t be interested in clean, free, renewable energy? And unlike other charging solutions such as solar panels or high-output alternators (which require sunlight or a running engine, respectively), wind-powered generators have the potential to generate free electricity 24 hours a day.

            This electricity can be used immediately to power equipment, but it’s normally stored in batteries for future use. Larger generators may develop enough energy under normal conditions to directly run larger loads, such as a small fridge or lighting during an overnight stay aboard, while smaller ones, generally speaking, produce only enough electricity to power a small bilge pump for a few minutes or top off your batteries after spending the weekend onboard.

            Regardless of model or size, all wind generators share a few basic parts: a rotor with aerodynamic blades, an electrical generator, rotating electrical contacts (which let the unit operate in 360 degrees), some form of rotor speed governor (this is optional on some units), and finally a mounting system, such as a pole or harness.

            Wind generators use either a DC motor or an alternator, and each have pros and cons. DC motors have brushes and commutators, both of which require periodic maintenance to prevent generation of electromagnetic interference, which can disrupt nearby electronics. Models with alternators initially produce AC voltage, which internal rectifying diodes convert to DC. These diodes are prone to damage if exposed to reverse-polarity voltages.

            Wind generators can usually be classified as either small rotor units, with blade diameters less than 48 inches, or large rotor units with blade diameters of 60 inches or more. Output varies according to blade size and the units themselves, but a rough rule of thumb is that larger generators (those with two or three 5-foot blades) generate around 4 amps per hour in 10 knots of steady wind, while those with 3-foot blades generate around a third of that, or 1.3 amps per hour. Although they have less output, small rotor units have the advantages of reduced size and weight, and they’re inherently easier to operate in high winds. The primary benefits of large rotor units are their increased power production and often quieter performance.

            Wind generators obviously depend on the wind, but at some point (typically around 35 knots of sustained wind) you’re approaching too much of a good thing. You need some form of blade speed control mechanism to prevent physical damage to the unit and overcharging damage to batteries. (Every installation should include some form of voltage regulation to prevent overcharging the batteries. Some units have built-in regulators, while on others you must install them separately.) Braking or blade speed control can be accomplished several ways. Some units have specially designed blades that stall out at certain speeds, while others are designed to gradually turn away from the wind if it becomes too powerful. There are also friction and air braking systems—the latter is considered more reliable at higher wind speeds. Finally, some generators require you to physically tie off the whirling beast—an unattractive prospect in a rocking boat, considering blade speeds can exceed 200 mph.

            While construction, size, weight and ease of installation are all important considerations, noise is often the deciding factor in what type you will choose. All wind generators make some sort of racket, but noise from some is on par with running an engine at anchor—which raises the question, why not just forget the wind generator and use your engine and alternator? A good way to compare noise levels of various units is to walk the docks of your local marina or dinghy around the mooring field and listen. This also lets you ask the owners (if they’re onboard) how they like their systems. Another way is to consult technical references on wind generators, such as the “Boatowner’s Mechanical and Electrical Manual” by Nigel Calder, which compares 13 of the more popular units you’re likely to encounter.

The Nature of Wind

            The main challenge confronting any wind generator is the unpredictable nature of wind itself—especially on the Bay. Battery-stored power helps meet electrical demand during calm spells, but the catch-22 is that wind generators are most effective in steady winds with the vessel at anchor—and most of us like to find nice calm coves for anchoring. So the “kick-in” speed of a wind generator—the point where it actually starts producing electricity—and its output in lower winds (10–15 mph or less) can be more important than maximum rated output. Multi-blade types have an advantage in this respect; smaller, lighter blades require less wind to start turning, meaning they’ll reach kick-in speed and start producing power sooner in light winds.

            The power of wind is another factor. If wind speed doubles, wind power—the level of work it can do—increases eight times. This means that if you’re anchored in that nice, quiet cove but every now and then a smart gust of wind blows through, the generator output can approach or exceed what you’d get while anchored in a steady, moderate breeze. This is where wind generators with larger blades and higher maximum outputs have an advantage—they can generate more power more quickly than smaller units. The variable here, though, is whether these puffs occur often enough to keep up with power demand.

            If you’re planning on generating while sailing, don’t forget that wind is not always what it seems. Downwind, for instance, you must subtract the boat speed from the wind speed to get the effective wind speed at the generator. If the true wind speed is 14 knots and boat speed is 7 knots, your generator is actually “seeing” only 7 knots, so output will be greatly reduced.

            Since wind on the Bay is an unpredictable animal, you might want to consider a hybrid system that combines wind generators and solar panels [see “Soak Up Some Sun,” Good Boatkeeping, May 2003]. Cloudy days are often accompanied by higher winds, while sunny days often mean lighter air. Using both methods may be the answer.

Location, Location, Location

            As with most equipment installations, choosing a location balances aesthetics and performance; your choice can look good but operate poorly, or vice versa. The best spots are those with an unobstructed flow of wind that at the same time keep whirling blades clear of rigging, self-steering vanes, davits, and crewmember appendages and noggins.

For convenience and safety, stern poles are a popular mounting choice. They hold the unit in place and ready for use anytime, while keeping it up and out of the way. Stern poles consist of a stainless steel or aluminum tube about 2 inches in diameter firmly mounted with rail clamps, guy wires and/or rigid metal struts to provide diagonal support from the pipe to the deck. Bracing is crucial for strength and to reduce pole movement, which in turn minimizes vibration and noise below decks. Aluminum tubing has its advocates; it’s lighter and easier to work with than stainless, and its flexibility tends to dampen vibrations. The downsides to stern pole mounts is the added windage, not to mention the “cluttered” look some purists just can’t abide.

            If you’re lucky enough to have a radar arch, or if you plan on installing one, you’ll find it is an excellent mounting spot for your wind generator. It gives you a wide latitude with placement, and you can even mount a generator on each side.

            If your boat has two masts you may be able to mount a wind generator two-thirds up the mizzen or all the way at the top. Both choices offer more exposure to wind and provide a cleaner looking deck, but they do add weight aloft. They also make it harder to reach the unit for service, and they’ll require longer cable runs, meaning you may have to upgrade to larger wire sizes to prevent voltage drops. Securing them will also be more of a challenge, particularly those that have to be manually tied off in high winds.  Rigging-suspended mounts, such as a foretriangle hoist, are a good alternative if you just can’t find a mounting spot elsewhere. This option produces less vibration, and units designed to be deployed this way can easily be removed and stored to clear the decks when needed. However, you can’t use them while under way.

            So, once you’ve selected a wind generator and found the perfect spot to mount it, will the benefits outweigh the effort? Well, your need for onboard electronic doodads will likely increase rather then decline—and fuel isn’t getting any cheaper. A good energy plan utilizing both wind and solar power can go a long way in reducing fuel expenses, as well as wear and tear on your engine when you must use it to charge up those batteries.

            As far as alternative energy sources for powering your boat’s systems are concerned, the best things in life really are free.

Frank Lanier is an FCC licensed Coast Guard electronics technician and owner of Captain

F. K. Lanier & Associates LLC Marine Surveyors & Consultants of Chesapeake, Va.