Power plucked from the air

Sail into any major cruising anchorage and you will see evidence of the trend in today’s sailing vessels: they are getting larger and more sophisticated, with multi-function navigation control systems, refrigerators, trash compactors, electric toilets, microwave ovens, and hot and cold pressurized water, drawn from the bottomless well of a watermaker.
With all these new marvels competing for their fair share of battery power, it is little wonder that wind generators — those little windmills standing high above sailboat sterns — and solar panels, have become nearly as common on voyaging vessels as anchors and deck winches.

Small vessels (25 to 30 feet) generally do not have high power requirements, especially that demanded by refrigeration, so they can generally get away with relying on the engine alternator and perhaps a large solar panel to keep up with a small GPS, a VHF radio and a single-sideband, as long as it used sparingly. During my circumnavigation on Saltaire, a 1966 Cal 30, I generally kept power usage below 10 amp hours per day.

At the other end of the spectrum, much larger vessels, measuring 50 feet or more on deck, often carry a small diesel generator to ensure a consistent source of power, not only for the highly complex array of 12- or 24-volt DC electronics, but also for appliances requiring 110 or 220 volts AC. Battery consumption of 200 amp hours per day is not uncommon on these larger vessels.

Between these two extremes lies the bulk of the world’s voyaging fleet: vessels measuring 30 to 50 feet LOA and generally having onboard a refrigerator and a marine single-sideband or ham radio, plus an array of electronic navigation systems, which together deplete a battery bank quickly under normal voyaging conditions. Boats in this broad category typically consume anywhere from 40 to 100 amp hours per day.

Many voyagers on these medium-sized boats avoid the high fuel demands of the main engine or genset by combining several solar panels with a wind generator. The logic speaks for itself: when it’s calm and sunny, the solar panels keep the batteries topped off. But as long as there is a breeze of at least 8 knots, the wind generator can provide an impressive amount of power, often far more than is needed.

On ocean passages, both wind and sun are effective sources of energy. You can expect plenty of wind and direct sunlight in the tropics, allowing your engine to rest for days on end. However, at anchor, local storms can engulf small islands for days, bringing strong winds and pelting rain.

A perfect example are the sultry conditions of Pago Pago Harbor, American Samoa, where storm clouds form over Rainmaker Mountain almost daily, hurling winds of 18 knots or more through the anchorage. Two miles offshore, it’s just another bright, sunny day with typical trade wind conditions. But inside the harbor, where it’s 107° F and raining buckets, wind generators on voyaging boats whiz away at warp speed, pouring out the life blood of ice makers, cabin fans and DVD players.

Incidentally, 85 percent of all the canned tuna consumed in the continental U.S. comes from the Star Kist and Chicken of the Sea canneries in Pago Pago Harbor. You can not begin to imagine what the place smells like when the canneries steam clean their exhaust stacks — all the more reason to have a few electric amenities to ease the suffering, and an aggressive charging system to keep them running.

Theory of operation
If you have ever watched a wind turbine, even a toy pinwheel, in a fair breeze, you have noticed the blades rarely spin at one speed for more than a few seconds. It will slow down to a near stop, and then as the wind gusts lightly, the turbine becomes a blur. This is because the power available from the wind increases with the cube of wind speed. So when the average wind velocity doubles, power is multiplied eight times. For example, a 5-knot zephyr will produce 125 units of power; at 10 knots, the power available zooms up to 1,000 units.

No matter how efficient a wind turbine’s blades may be, though, according to Betz’ Law, the maximum amount of kinetic energy that may be drawn from the wind is less than 59 percent of the wind’s total power. This theoretical ceiling results from drag and power dissipation occurring on the downwind side of rotor blades.

Other sources of mechanical inertia place further limits on the harnessing of wind power. Minor flaws in the design or manufacture of rotor blades, the type of generator employed, wear and tear in shaft bearings, and turbulence caused by nearby objects conspire to make some wind generators perform better or worse than others. Knowing about the different types and builders of wind generators, and how to install one of these gems properly, can make a big difference in the service you can expect from your selection.

Design features
In selecting a wind generator, make sure you match the output to fit the general range of power required by your vessel and the amount of wind you expect to find in your cruising grounds. One model may promise two amps at 10 knots of wind, but will it blow an average 10 knots around the clock where your boat will be voyaging? Certainly it would be naïve to plan on consistent 48-amp-hour days with that model. At the same time, a small boat using a conservative amount of power for a well-insulated refrigerator and a minimum of electronics does not require a unit producing 6 amps at 10 knots.

 Two common complaints with wind generators are interference with AM receivers, and vibration and noise produced at high wind speeds. Radio interference is caused by non-marine generators employing brushes that produce tiny sparks as the stator brushes rub against the revolving armature. The solution to the resulting static is marine-grade brushless generators designed to prevent sparking. Before purchasing a wind generator, be sure to ask your sales representative to inform you of the type of generator used, as this information is not always mentioned on Web sites or in sales literature.
 Vibration from the spinning rotor can be a problem with some models, even at moderate speeds. Find out first from another owner of the model you wish to buy whether vibration is a problem. Having anticipated this problem, most manufacturers include rubber mounts with their installation kits.

The high-pitched “wheeeâ€� sound is produced by air cavitation on the low-pressure side of rotor blades spinning at high speeds, generally in winds in excess of 30 knots. Orville and Wilbur Wright struggled with blade profiles for maximum efficiency on their historic airplane Flyer I more than a century ago. Their research formed the basis for today’s airfoil shapes, and scientists are still pursuing the elusive perfect blade. Adjusting blade pitch is but one strategy gleaned from aviation research in order to reduce drag and noise. Some wind generators feature microprocessor-controlled blade pitch feathering for reduced drag in high winds. Pitch control also controls speed, in turn reigning in excessive output.

Leading manufacturers
The wind generator industry is populated by dozens of manufacturers, a few of them producing large industrial models to be tied into community and regional power systems. Fortunately, a handful of these companies have found a ready market among us cruising sailors who look for alternative energy sources, not to be politically correct, but to save on fuel costs in the long run.

According to its builders, the Air-X is the world’s biggest-selling marine wind generator, and a quick walk around any marina or anchorage in North America, the South Pacific or the Caribbean will confirm their claim. The Air-X, built by Southwest Windpower in Flagstaff, Ariz., lies at the middle of the pack in overall output, but its power curve rises quickly to a respectable 12 amps in 20 knots of wind.

A recent improvement in the Air-X’s design is its carbon fiber composite blades, spanning 46 inches. This construction renders the Air-X lighter than units with aluminum blades, and more resistant to the ravages of wind, sun and salt. Earlier versions used plastic blades that stretched as wind velocity increased, operating as a centrifugal governor against excessive, potentially damaging speed. Unfortunately, the old blades were noisy at wind speeds of more than roughly 30 knots.

The latest-generation Air-X electronically controls rotor speed in high winds, putting the blades into a slow, silent spin until wind speed drops. The unit comes with a sealed, brushless alternator, and an internal, three-phase, microprocessor-controlled voltage regulator instead of the more common shunt regulator, which relies on heat dissipation to bleed off excess power. A three-phase regulator allows a high “bulkâ€� charge when batteries are low, a “taperedâ€� charge when the batteries are close to maximum capacity, and finally a “floatâ€� charge at reduced voltage to prevent overcharging.
The total installed weight of the Air-X, including bracing poles, is less than 35 pounds, and the whole kit, with an extra set of rotor blades thrown in for good measure, comes to a bit less than $1,600.

The Ampair, built by Boost Energy Systems in the U.K., is in the same size and weight range as most of its competitors, and produces a power curve almost identical to that of the Air-X up to about 27 knots wind speed, after which the Air-X reduces its speed until the wind drops. In a light gale of 32 knots, the Ampair puts out a whopping 25 amps AC. The three-phase Ampair 300 features a sealed, brushless alternator, a DC rectifier, and blades constructed of glass-reinforced polypropylene.

A key component of the Ampair is its PowerFurl blade pitch control system, which prevents excessive spinning speeds while maintaining power output. This is designed to eliminate the vibration and screaming we associate with improperly designed or managed rotor blades.

The KISS generator, manufactured in Chaguaramas, Trinidad, is a high-output machine cranking out a full 4 amps in a 10-knot breeze. That comes to 96 amp hours per day, if the wind holds steady, in air that is hardly strong enough to blow away a house fly, much less a tenacious mosquito.

In 15 knots of wind, The KISS puts out an impressive 10 amps of power, more than most voyaging vessels can use if averaged over 24 hours. In 25 knots of wind, it produces 25 amps — that’s an amp per knot — or 600 amp hours averaged over a 24-hour period.

The KISS does lack tapering blades or an automatically braking rotor. A crewmember will have to keep an eye on the battery monitor to prevent overcharging. When the batteries are topped off, the unit may be turned away from the wind manually to prevent overheating and overcharging.

Everfair Enterprises of Punta Gorda, Fla., manufactures what is arguably the highest-producing wind generator available to ocean voyagers. The FourWinds II/Red Baron beats all competitors in its range at every wind speed from 5 to 20 knots. Only The KISS produces a higher level of current at 25 or more knots. Most of us want to start tapering off the charging output well before that point anyhow, so these upper-end comparisons are essentially academic.

Fellow voyager Dick Verbeck picked up a used Red Baron for his 34-foot, heavy-displacement, Bruce Roberts-designed cutter Beatitude for the give-away price of $60 at one of the swap meets held periodically at Chula Vista Marina in San Diego Bay. After purchasing mounting poles and stainless steel fittings, he had invested a mere $200 for a machine that keeps two 6-volt golf cart batteries and two 12-volt 8-D batteries, with a total battery storage of 800 amps, fully charged.

Dick’s refrigerator consumes a maximum of 20 amp hours per day, and navigation lights and instruments deplete another 25 amps for a total of 45 amp hours. He says with anything more than 10 knots of apparent wind, the batteries stay topped off with all these systems running. “At 12 knots, we can bump up to the autopilot for coastal cruising,â€� he adds.
For passages from Los Angeles to Hawaii, Dick deploys a Sailomat servopendulum self-steerer rather than running the electronic autopilot, which he says is inadequate for offshore conditions. The Sailomat uses zero electricity yet steers better than any helmsman could on long hauls, so he has even less need of cranking up the “iron jib.â€� Here again, we see wind power offering solutions to our energy needs on offshore voyages.

A unique option offered with the Red Baron is a conversion kit for deployment as a water generator. This set Dick back only another $150, and the configuration covers all daily power requirements with only six hours of charging at a boat speed of 6 knots. Because water is many times denser than air, water generators are capable of significantly higher amounts of current. While at 6 knots of wind the Red Baron produces 1.4 amps, at 6 knots water speed, that figure jumps to eight amps. When the batteries are charged, Dick simply hauls the turbine up on deck until the following day.
Essential to this system is an optional, three-phase, “smartâ€� microprocessor-controlled regulator, which keeps the battery banks from frying. Installed on the engine box bulkhead, immediately below the controller, is a junction box Dick devised to house a diode preventing accidental discharge and a fuse protecting the wiring.

As we tallked in Beatitude’s cockpit, the wind picked up to around 12 knots, and Dick flashed a big, toothy smile. “Listen. Do you hear anything?â€� I looked up at the Red Baron’s rotor blades gently slicing the air, and all we could hear was the distant, muffled squawk of a sea gull. The Red Baron was absolutely silent.

Marlec, of the U.K., offers the small yet popular Rutland 913, which produces roughly 1.7 amps at 10 knots of wind, 6 amps at 20 knots, yet whose blades cut only a 36-inch-wide footprint. A molded, six-blade rotor makes efficient use of the wind, ensuring what Marlec claims is the lowest wind start-up speed of any wind generator on the market — only 5 knots of breeze.

Fiberglass-sealed magnets and stator coils protect the generator from the elements and eliminate AM radio interference, and “automatic thermostat protectionâ€� guards against damage to the generator in gale conditions.

Particularly interesting is how the 913’s blades and internal design combine to produce what Marlec calls “a high-inertia generator whose flywheel effect generates smooth, continuous power between gusts when other wind turbines have lost the power in the wind.â€�

The 913’s smaller, lower-priced sibling, the Rutland 503, was designed for sailing vessels less than 30 feet LOA, in which battery charging demands are generally meager compared with those of larger yachts. Its diminutive turbine, measuring a mere 8.9 inches in diameter (smaller than the average frying pan), generates a trickle charge at a wind speed of 5 knots and a full two amps at 19 knots, more than what you can expect realistically from a 36-watt solar panel, even on a cloudless day at latitude zero.

The Rutland 913 and 503 both incorporate a three-phase shunt voltage regulator coupled with a controller, ammeter, LED voltage level indicator, blocking diode and fuse, all of which are housed in an attractive white plastic box. The 913 control box also includes a selector switch for one or two battery banks.

The choice
An important point to keep in mind is the more battery storage your vessel has, the more you will be able to take advantage of the charging power of a wind generator, particularly of the high-output variety. The choice should be directly related to the charging needs of the vessel and the specific features of the unit, not solely to price, much less to appearance, although some models are decidedly easier on the eyes — and ears — than others.

As a final note, the $1,000 to $2,000 you spend purchasing and installing a new wind generator can buy a lot of diesel fuel (500 to 700 gallons at current U.S. fuel dock prices), but a gallon of diesel still weighs approximately seven pounds. This equates to nearly half a ton at 140 gallons, as opposed to an installed weight of less than 40 pounds for the typical marine wind generator. One more thing: with global warming and the world-wide scramble for dwindling oil reserves, it’s nice to know there is something we can do as individuals to help make our world a little cleaner and perhaps just a tad more peaceful at the same time.

By Ocean Navigator