David,

lovely piece of work, though not completely sure how it operates, are you going to bless us with a diagram?

One point that has always interested me is the best section for the vane,  I assume flat (as most are / were) is not that good - You have a fat leading edge - would there be a benefit from curved faces?  (A shaped piece of Styrofoam between the cloth should work?) 

Best wishes

It's high time that I began to unveil the vane gear I've been making for Weaverbird. No, it's not going to be the Willing Griffin style of "auxiliary rudder that looks like a trim tab", after all. It's my take on the Hebridean principle of operation. I think that this principle is a genuine advance in vane gear design, but its embodiment, I thought, was in need of a lot of simplification. 

The photo shows the gear almost complete and ready to be installed. From right to left:

• The vane comprises a frame of carbon fibre tubes, 10mm at the sides and 6mm at the top, in a V formation to put the centre of area well away from the axis; covered with a sleeve of 92gsm ripstop polyester cloth.
• There is an integral drum, 80mm diameter, with acetal bearings. It is mounted on a shaft of 5mm stainless steel rod.
• The vane axis supports are mounted on a large "sheave" made of discs of plywood, so that course adjustment lines can be lead forward.
• Primary linkage lines of 2mm Dyneema will go from the drum down to the servo blade.
• The power axis is at 45 degrees to horizontal. I have used Seasure pintles and gudgeons for this, and the mounting for the gear will clamp onto a tube that will be fixed to the transom of Weaverbird.
• The servo blade carrier is made from strong, stable hardwood, section 63mm x 25mm. It carries the base for the course adjustment sheave, and also the Seasure pintle and gudgeon for the axis of the servo blade. At the bottom, there is an Antal low-friction ring, which turns the 2mm Dyneema primary linkage cords from the vertical direction as they come down from the vane, to horizontal as they go out to attach to a triangular plate on top of the servo blade.
• Not easy to see in the photo is a transverse member of pultruded GRP, to which the secondary linkage cords of 4mm Dyneema will be fastened. These will lead through blocks on the transom to a point on the back of the rudder.
• The top part of the servo blade is another piece of strong, stable hardwood, section 63mm x 25mm. It is strong bonded and dowelled to the underwater part of the servo blade. This is assembled from solid pultruded GRP sections: 10mm diameter, rectangular 50mm x 12mm and rectangular 45mm x 6mm, all faired in together to form a foil section.

• The vane has a lead counterbalance weight that is heavy enough to centre the vane, even if wet with rain or spray.
• The 45 degree angle of the power axis means that the servo blade has a strong trailing action.
• The servo blade has neutral mass balance about its axis, so that when it swings out to one side, there is no tendency for it to rotate to a larger angle of incidence due to having its CG aft of its axis (this feature is missing in the original Hebridean).
• The servo blade is denser than water, so that it will not tend to float up to one side or the other. 

Slieve McGalliard wrote:

A good analogy, David.

I like your analysis of the various gear types. My fag packet involves an inclined power axis, as you call it, as I have experience of a CapeHorn gear that would not drive itself despite being installed by the designer. I only saw it in action for about an hour in a near flat calm, so we were motoring and drifting to get a clear water flow. The only explanation I could find for its behaviour could be that it may have had forward rake which I could not judge from on board the boat.

Fickle things, boats.

Cheers, Slieve.

Ah, that might explain it - a long thin boat is not so inclined to yaw. Think of a Greenland kayak.

But the Splinter 21 and the Duette 23 have virtually no yaw damping of their own. In increasing order of adding yaw damping with a vane gear:

1. Horizontal axis vane direct to tiller - no yaw damping at all.
2. Trim tab on the main rudder - not very effective, but can be OK on a heavy, long keeled boat.
3. Fixed main rudder with an auxiliary rudder - better, and good enough for many modern boats, as demonstrated by the Hydrovane.
4. Servo pendulum with horizontal power axis - better still. Common examples are Aries, Monitor, Fleming.
5. Servo pendulum with inclined power axis - the only commercial example I know is the Windpilot. Tystie's gear has the power axis at 30 degrees to horizontal, and can be driven quite hard downwind. Fantail's gear has the power axis at 45 degrees, but it can be difficult to devise a linkage for that angle.
6. Servo "gate" with vertical power axis (actually, 4, 5 and 6 form a continuum) - best of all but really too much yaw damping for most boats; the arc of servo movement is quite small, as well.