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Wind Powered Generators for Catamarans

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Sailors have known for centuries that wind energy can be harnessed to propel boats, but only recently has it become accepted that the energy in the wind can also be used to create clean, renewable electrical power on board.   

Wind-powered generators for marine use were introduced in the mid-1970s, and they have been constantly improving since then.  Wind units currently on the market can produce a formidable amount of electrical power, but only you can decide if wind power is right for your needs and, if so, which particular model is best.

All wind generators consist of a rotor with aerodynamic blades, an electrical generator, a tail vane to keep the unit facing into the wind, and some type of protection against overspeeding in high winds.  Recommended accessories include a charge controller to prevent battery overcharge and a monitor that displays charging amps.  A few wind units can also be converted to a trailing-log water generator for downwind passages, when the apparent windspeed is low. 

There are two basic wind unit types, small-rotor and large-rotor.  In general, small rotor units such as the Ampair have multiple blades, a blade diameter of less than 48 inches, and relatively low average output.  The advantages of this type of unit are reduced size and weight and inherent overspeed protection in high winds. Small-rotor units are good for light electrical loads or as a complement to other charging sources, although many sailors in areas with unreliable winds are opting for a large solar panel that can have the same or greater average output at less cost and with no moving parts. 

Large-rotor units such as the Ferris Windpower 200 have 2 or 3 blades, a blade diameter of 60 inches or more, and high potential output.  The main advantage of this type of unit is the high output, although you still need to have reliable winds for good average performance.  (You may be cruising in the trades, but if you like to anchor in the coziest part of the harbor you probably won't have exposure to reliable wind.)  Most large-rotor models are also relatively quiet and have either standard or optional overspeed protection.  Large-rotor units are most popular with cruising sailors who have refrigeration and other large electrical loads.

The new Air Marine unit is something of a cross between a small and large rotor type.  Its sleek design, small size, high rated output, and unique feathering plastic blades have created a great deal of excitement, but beware—there have been a multitude of complaints of excessive noise and much lower-than-rated output.   

Wind units can be mounted temporarily in the fore or main triangle (mostly combination wind-water units), or permanently on a pole or arch at the stern or on the mizzen mast.  They should always be mounted well above head and hand height.  Integrating a wind unit into your independent power system is easy, since the output is compatible with other renewable and engine-driven charging sources and all monitoring systems.


Part II - Mounting a Wind Generator

Wind generators are high-capacity battery chargers with the ability to supply a large part of your electrical load.  If a survey of your specific electrical power needs convinces you that a wind generator should be part of your charging scheme, you'll eventually face the decision of how to install it properly on your boat.  Your choice of mounting method depends somewhat on the type of unit you select. 

There are several "small-prop" and several "large-prop" wind units currently on the marine market.  The small-prop units, including the Air Marine, Ampair, Rutland and Aerogen, have prop diameters of 48 inches or less, while the large-prop models, including the Ferris WP200, Fourwinds, and Windbugger, have a prop diameter of around 60 inches.  Of these, the Ferris WP200, the Fourwinds, and the Ampair can also be converted to a water generator for blue-water passages.  Keep in mind that wind generator performance falls off dramatically on a downwind passage due to light apparent winds.

The most common method of installation is to mount the wind unit on a pole at the stern, but other viable mounting methods include a rotating mizzen mount, a fixed mizzen mount, and a rigging-suspended mount.  Each mounting method has its advantages and appropriateness for a particular situation.  Some things to consider for each method of mounting are: safety, performance, strength, convenience, appearance, cost, and potential noise and vibration.  In this issue we'll review the stern pole mount for a wind-powered generator.

Both small and large-prop wind units work well in a stern pole arrangement.  This mount is semi-permanent in that there is nothing to set up or dismantle on a routine basis, although you may remove the generator to convert it for water use if your unit is so equipped, and you may choose to lower the pole during a long downwind passage or a storm. 

A professional wind unit stern pole kit supplied by Ferris Power Products illustrates the type of components needed:

  • An anodized aluminum mounting pole (typically 9-10 feet of 1.5-inch schedule 40 aluminum tube)
  • Two stainless steel support struts (8-foot long x 1-inch diameter)
  • An aluminum deck plate for attachment to the stern
  • Miscellaneous hardware
  • Rubber isolation pads 

The pole itself can be either aluminum or stainless steel.  Aluminum poles should be anodized or painted to keep them looking nice.  A polished stainless steel pole is more expensive per pound, but the overall cost is comparable since the extra strength allows for a thinner pole wall thickness. 

On a stern pole the wind unit must be mounted well above head and hand height, and even then caution must be exercised to keep lines and other objects clear of the rotating blade.  Something in particular to watch out for is a close encounter between your boat and another craft with higher decks.  To those on the other boat your wind unit will seem much lower, and can be dangerous. 

Mounting the pole to port or starboard on the stern allows for best access to an uninterrupted windstream and keeps the center clear for a steering vane and other gear.  If you must mount the pole on the center of the stern, count on a slight loss of efficiency due to wind turbulence caused by the mast(s).

Metal struts keep the pole rigid, a must for this type of mount.  Attach the top of the struts to the pole just below where the tip of the wind blade passes, and place the struts 90 degrees apart to keep the pole from vibrating.  Attach the bottom of the struts to the deck at any convenient location.  For maximum stiffness try to keep the strut at a 45 degree angle to the pole and the deck.

Through-bolt the deckplate and strut ends using a backing plate if possible.  To minimize noise and vibration belowdecks, make sure to place pads of rubber between any part of the pole assembly (deckplate, struts, etc.) and the decks or rails of your boat.  Cut the rubber pads to fit and put them in place before installing the deck fastenings.  Place a pad anywhere the struts cross stanchions or the stern rail.

Installing a thin nylon strap to the pole about even with the midpoint of the wind blade makes it convenient to tie off the blade if desired.  And a sturdy electrical deck plug, rated for the maximum current of your wind unit and placed near the base of the pole, provides a handy means of disconnect.

There are several other good mounting methods other than mounting it on a pole at the stern, including on a mizzen mast or simply suspended in the rigging.  Let's review what's involved with these mounting methods.

A mizzen mast is a convenient mounting place that keeps the wind unit well away from the crew and the assortment of boat gear that tends to accumulate around the stern and up where there is good access to the windstream.  In fact you'll get roughly fifteen to twenty percent more power from a wind unit mounted 30 feet or more above the water.
There are three methods of mounting a wind unit to a mizzen mast.  Small-prop wind units can be mounted on a short pole attached to a bracket extending from the forward face of the mizzen, similar to a radar mount, or on a short pole at the top of the mast.  Either location allows them to rotate freely to seek the wind.  Large-prop wind generators—those with a blade diameter of five feet or more—are usually fixed-mounted to the forward face of the mizzen.  Their size and weight make it undesirable to mount them at the masthead or extended far enough out from the front face of the mizzen to allow for 360 degree wind-seeking ability.

Mizzen-mounting a small-prop wind unit requires the installation of a custom bracket and a short length of pole, usually a 1.5" I.D. (inner diameter) schedule 40 aluminum tube that is slightly longer than half the prop diameter.  For mounting on the mizzen's forward face, the distance between the centerline of the pole and the mast must be slightly more than half the prop diameter.  These clearances allow the wind unit to rotate freely in all directions without hitting the mast or the mounting bracket.  When selecting a mounting location, care should be taken to avoid masthead fixtures, side stays and other rigging lines.

Large-prop wind units fixed-mounted to the mizzen are less expensive to purchase and mount, but they rely on the boat at anchor or mooring to seek the wind.  A small bracket will still need to be fabricated to secure the generator to the forward face of the mizzen.  Most generators for this application have four bolts in the front face of the unit surrounding the shaft.  These bolts can be used to secure an angled bracket that is also attached to the mast.  A variation on this theme is to mount a large-prop wind unit so it can rotate 45 degrees or so in each direction off centerline to seek the wind when at anchor or mooring or when sailing close-hauled.  You'll need a wind unit with slip rings, as well as a mounting bracket with positive stops to prevent excessive rotation of the generator and prop.  Make sure the stops are cushioned to avoid damage in rough sea conditions.  Mount the wind unit on a short stub of pole—6 to 8 inches high should be sufficient—that is welded to the mounting bracket. This option will cost more initially, but will allow the unit to track the wind more efficiently.

All mizzen-mounted wind generators must have foolproof overspeed protection to protect the unit in high winds.  This is especially true for a large-prop model, since there is no convenient way to feather the prop out of the wind.  Output wires for the wind unit can be run down the mast to a deck plug.   

Rigging-suspended mounting is popular with bluewater cruisers who have a combination wind- and water-powered generator.  Mounting a rigging-suspended wind unit is easy once you've figured out the attachment points and how long to make the tie-down lines.  The fore-triangle area is most often used for this application; the main triangle can be used but the main mast tends to cause turbulence in the airstream.  You'll need a halyard with snap shackle to haul the unit up, a line from the top of the wind unit frame to the forward stay for proper positioning, and three tie-down lines to prevent movement.  In the initial set-up, make sure the unit is plumb in both a fore-and-aft and side to side axis, and that the prop doesn't come anywhere near other rigging lines.  A deck plug is typically mounted in some convenient location nearby to keep the deck clear of wires.  

Independent Energy GuideKevin Jeffrey is a long-time multihull sailor, independent energy consultant, author and book publisher.  He is the author of Independent Energy Guide, a valuable resource for cruising mutihull sailors, and is the publisher of Adventuring With Children by Nan Jeffrey and the first three editions of the Sailor's Multihull Guide. Sailors Multihull Guide

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