Hebridean Wind Vane History

In response to requests by builders of the Hebridean Wind Vane for more information on John’s journey of discovery, I am publishing this short article he wrote in January 2015. He was tenacious in the face of complex challenges and determined to find simple answers for the DIY builder. 

Hebridean History
by John Fleming

I have been using my wind vane for about 7 years now (time of writing 2015) and it has worked in all the conditions I have encountered. Last summer (2014) we were having gusts up to 50 knots and it coped fine. Big waves don’t seem to bother it. All it is doing is registering a change in apparent wind direction and reacting accordingly.

When needed, the rudder action is far from impotent as when in rolling seas or on the run in big waves etc., and this is clear from video 1 (I would say). In big waves the wind vane pendulum follows up and down with the boat as if it is a flat calm, so no different. Being a servo pendulum it naturally opposes yaw.

I have no experience with the USD system but I have been in contact with Jan Alkema who designed it. With a spade rudder (as is mine) you sometimes have to be aggressive with the tiller when running in big waves to keep it on track. The Hebridean is good at this on account of the vane being mounted on a horizontal axis which in itself is not damped – only when the pendulum swings. This does make the Hebridean different to all others – with distinct advantages in my view but difficult to explain.

When considering building my own wind vane some years ago I knew little about how they worked. All I knew was that for a DIY builder to affix the vane axis (vane attachment) rigid to the boat – as it is in all other systems – it would be difficult to create a connection with the pendulum, which has to swing to the side to correct course. Sailomat patented a method of connection. Walt Murray has a method but his too is difficult to make work, involving bent wires, etc. Cogs solve the problem easily (Aries, etc.). But that is engineering.

I therefore configured the Hebridean so that the connecting push rod swings with the pendulum – simple!

It was then that I discovered the vane was rotating as it swung. Was this to be an insurmountable problem? I later observed that it was always rotating into wind, a feature that could potentially be utilised to damp the vane instead of having the axis inclined 20 degrees. All I then did was build a model and fiddle around with the angles until it rotated the vane axis equivalent to one on a fixed base inclined 20 degrees to the horizontal.

I also designed the frame so that the vane base did not sway too much. That is why the base is on a shaft (the “extension”) leaning backward with connection to the pendulum low down. It also lowered the centre of gravity which in my case is important.

So you could say I discovered the design by accident. I made the wind vane, stuck it on the boat, and it worked. Since then I have discovered that I have got all the angles right mathematically, and checked by Jan Alkema and his formulae. So I don’t need to change anything by the looks of it.

The vane is damped by positive rather than by negative feed-back which has its advantages. Level of vane damping changes according to conditions as it is delayed. Indeed the vane axis being horizontal can result in greater vane rotation for a given course error than at other times when the boat is moving fast through the water (which is when the delay is minimal). This means that the vane works well when the going gets tough, reducing boat speed despite strong winds (greater delay).

1. The push rod swinging with the pendulum;
2. on a frame that pivots;
3. in a socket attached to the boat;
4. makes construction simple for DIY sailors;
5. providing a system that can be lifted off and on as a complete unit weighing only 12kg.
6. It can then be folded flat, the pendulum removed and the unit stored in a boat locker.

I tested it to 350kg by pulling side-ways on the pendulum until the force in the lines to the tiller reached 350kg (in this case the lines were tied off). A force of around 85kg on the end of the pendulum was necessary to do this. When forces reach this level then the pendulum is pulled out of the water against friction in the socket. If the weak link in the system (a safe-guard) breaks at 100kg in the lines to the tiller, then friction is enough to keep the pendulum in the water. This friction is enough to hold the pendulum out of the water when motoring. If the pendulum is pushed out of the water by something floating then the pendulum has to be pushed back in against friction to continue to work as before as if nothing had happened.