The steering impulse in a windvane gear comes from the windvane. The vane takes its energy from the apparent wind flowing across its surface at the angle set. There are two types of vane, the horizontal vane and the vertical vane.
The Vertical or V vane rotates about a vertical axis (the same principle as a weather vane). It always points directly into the wind, so the effective windvane area (the area actually subject to the action of the wind) is never very big. When the boat strays off course the windvane is deflected by no more than the amount in degrees of the deviation. The steering impulse generated by this deflection can only deliver a limited amount of force since a V vane generates little torque.
Adjusting a V vane to the wind direction could hardly be easier: when free to rotate, it always points exactly into the wind and requires no special setting. It can be adjusted for different wind strengths just by moving it in or out along its mounting bracket. Increasing the distance between the vane and its shaft (longer lever) gives increased power for light airs. Reducing the distance (shorter lever) helps to reduce vibrations in the vane gear in heavier airs when power is not a problem.
Air flow across a vertical windvane is always laminar, so aerodynamic sections or wedge-shaped designs with flow separation edges are the most efficient shapes. Not only are both alternatives heavy but they are also complex and expensive to build, so almost all manufacturers prefer simple flat designs.
V vane, Windpilot Atlantik auxiliary rudder system
V vane, Windpilot Atlantik auxiliary rudder system
V vanes need to be quite large in area (up to 1m2 / 10 V2 ft2) to enable them to deliver satisfactory steering impulses as well as the necessary steering force. They take up a quite alot of space on the transom owing to their size and turning circle, so permanent backstays, mizzen masts and davits can easily get in the way.
Wedge-profile V vane, Saye's Rig Counterweight
Because of its substantial size and weight, a V vane should be perfectly balanced by a counterweight. This is particularly important in the light air position since otherwise steering impulses can be generated by the heel of the boat. It is less critical in the heavy air position when the vane is up against its shaft because the stronger winds will exert enough force to counter any disturbance from the motion of the boat.
The following use vertical windvanes: Halser, RVG, Saye's Rig, Schwingpilot, Windpilot Atlantik/ Caribik.
A horizontal or H windvane rotates about a horizontal axis. When it is pointing directly into the wind it stands upright. When the wind strikes it from the side, i.e. when the boat is off course, it tilts to one side. What distinguishes this type of vane is the fact that when a course deviation occurs the wind strikes it over the whole of one face rather than just along the leading edge. As a result it has a substantially larger effective windvane area. H vanes are therefore able to exert considerably more leverage than V vanes and are said to be about 5.6 times as efficient.
Almost all horizontal vanes have adjustable fore and aft inclination. The upright position offers maximum effective area for the wind, which is desirable in light air. Inclining the vane aft, away from the wind, as the wind strength increases helps to reduce lateral swinging movements, allowing the gear to operate more smoothly.
Because a horizontal windvane obtains its force from the wind striking the side of the vane, there is nothing to be gained by using anything other than a flat section.
Many of today's horizontal vane systems use plywood vanes fastened to some kind of mounting bracket. Plywood is a relatively soft material so to prevent damage in strong winds there should ideally be a large contact area between the mounting bracket and the vane. The vane should also be easy to remove as the lazy skipper will otherwise be tempted to leave it fitted even in harbour, leading to unnecessary wear or breakage when it is not even in use. Many ARIES vanes have been left in place for years once the skipper realised removal entailed disassembling the entire locking device. The Sailomat 601 gear has the windvane inserted into a slotted aluminium tube, an arrangement that provides very little contact area between the mounting bracket and the vane. Monitor vanes are removed by undoing a pair of bolts. The Windpilot Pacific mounting bracket provides a large contact area with the vane and has a slot which allows quick removal of the vane once the locking device has been loosened one complete turn.
H vane, Windpilot Pacific Plus double rudder system
A horizontal windvane needs to be perfectly balanced by a counterweight to prevent spurious steering impulses caused by the motion of the boat. In practice this means the counterweight should be very slightly heavier (between 10-30 g / 1/3-1 oz heavier is normally sufficient) than the vane it is intended to balance. Some sailors attach rubber bands to the counterweight on traditional servo-pendulum systems to help restore the windvane to its neutral position. While this measure can offset the substantial inertia of the push rod, it does not increase the sensitivity of the system.
Because of its considerably greater efficiency, an H vane can be much smaller than an equivalent V vane. It is possible to change vanes according to wind strength, but this only works if the counterweight is changed at the same time. In any case, modern servo-pendulum gears are sensitive enough that one vane is adequate for the whole range of wind strengths. Almost all manufacturers specify an H vane area of 0.17 m2 for servo-pendulum gears and 0.25 m for auxiliary rudder systems.
Plywood has several practical advantages as a material for H vanes. It is light, cheap and robust and a plywood vane can easily be replaced using tools common on most boats. Be prepared to replace the vane. Weigh it and note the result - every replacement vane must weigh exactly the same. A plywood vane can be lightened simply by sawing a piece off. If you must have a larger windvane especially for light airs, the weight can be kept down by cutting large holes in the vane and covering them with spinnaker cloth.
■ Tip: A strip of spinnaker cloth (approx. 2.5 x 80
cm) stuck to the upper aft corner of the vane works wonders in light airs. Its fluttering action accentuates the movements of the plywood vane, which can otherwise become a little lethargic in very light conditions.
A horizontal windvane generally offers a smaller effective working surface to the wind and is easily handled and removed. H vanes also require relatively little operating space. They generally have no problem with yawl and ketch rigged yachts and even davits rarely interfere.
A strip of spinnaker cloth stuck to the vane works wonder in light airs.
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