We all know there is energy in the wind; we see its power in a number of ways, including as a source of propulsion for our sailboats. Yet extracting that mechanical power and changing it into electrical power available via the batteries is not as straightforward as it sounds. On an average size sailboat, the cost, performance, size, weight, maintenance, and noise are all considerations that must be taken into account when considering the purchase of a wind generator. And despite roughly 25 years of wind-charger use in marine applications, there are still compromises to be made in order to take advantage of this renewable resource. Sailors who are able and willing to make these compromises are rewarded with a steady supply of free electricity.
In mathematical terms, the maximum amount of electricity you can produce from a wind charger is proportional to the square of the blade diameter (i.e. the total swept area of the rotor) and to the cube of the wind speed. In simple terms, this means that although the blade size is an important factor in wind-charger output, wind speed is even more critical, and this relates to where and how you cruise. Some cruising grounds, such as southern Florida and on down through the Caribbean, have very good average wind speeds, while other regions such as the Chesapeake Bay have low average wind speeds during the cruising season.
When sailing, average apparent wind speeds are good when the wind is forward of the beam, but not so good when the apparent wind is well aft. In fact during downwind passages wind-charger performance, on average, is abysmal. And remember, the winds can be steady and strong in one anchorage (or in one part of the anchorage) that has good access to the wind, and variable or turbulent where the wind is blocked by trees, buildings, and headlands. Variable or turbulent winds don't have near the available power as winds with a clear fetch.
In addition to choosing a wind charger for its electrical output, it's also important that the unit satisfies your sense of aesthetics and preferred method of mounting. These may seem like quite different considerations, but aesthetics are greatly influenced by the way you mount your wind generator.
There are three main mounting variations from which to choose. The most common wind generator mount in use today is the stern-pole mount. In this mount a stainless steel or aluminum tube roughly two inches in diameter and long enough to keep the wind blades above head and hand height is mounted to the stern and held firmly in place by two or more rigid metal struts. It is critical that the struts keep the pole from moving in all conditions in order to minimize the noise and vibration transmitted below decks. The advantage of a pole mount is that it always keeps the wind generator in position and ready for use. The downside is that it causes additional windage and clutter on a passage.
My personal favorite wind-generator mount is a rigging-suspended mount that hangs the unit in the foretriangle when you are in port, allowing the unit to be stowed below before you put to sea. The advantage is that, with the unit suspended in the rigging and held in place by lines instead of rigid stays, much of the noise and vibration is eliminated. This mount also frees up the cockpit area when in port and allows for clean decks on a passage. In addition, the rigging-suspended wind units on the market can typically be converted to water generators when underway.
Whichever mount you choose, make sure you follow the common sense rules of safety when using a wind generator on a sailboat. By taking simple precautions, and adjusting your cruising so you have good average windspeeds available, you'll make the most of having a marine wind generator.
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