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Hydrovane: A Question of Balance

Updated: Sep 20, 2023


Banksys artwork in Ukraine showing david throwing Goliath
Banksys artwork in Ukraine showing david throwing Goliath

Judo is a sport all about balance. A judicious touch, push or pull, executed in the right place at the right moment, can cause huge weights (your opponent) to move in ways they least intended. I was reminded of this by the recent Banksy artworks which appeared in Ukraine after the liberation of Kherson. Apart from the obvious symbolism, the picture of  'little guy throwing much bigger guy'  beautifully illustrates what timing and balance can achieve.


Which is perhaps a tenuous introduction to a piece about the Hydrovane self-steering on Skyfall. Let me explain. Clearly, if you want to carry your home around the world with you, it is going to be heavy. Skyfall is (loaded) the best part of 16 tonnes. And to move such a heavy object, as quickly as Skyfall sails, requires quite some power. The power comes from the sails. I forget the actual square metres of sail but the photo below makes the point.

Skyfall sailing goose-winged downwind
Skyfall sailing goose-winged downwind

So what if someone told you that they could build a system where the power to control all this weight and all this sail, would come from a small vane with about half a square metre of area? "Impossible!", I hear at least some of you exclaim. But it is possible: with a hydrovane system and a boat 'in balance'.


There is a small vane which is angled into the wind.The vane is fixed to the boat so if the boat changes course then the angle of the vane to the wind changes. The wind now exerts more pressure to one side (or the other), pushing the vane down. This force is transmitted, via a gearbox, to move an auxiliary rudder mounted below.  But the force from the vane is tiny. Firstly the area of the vane is small. But, more importantly, you need a rudder correction with a course change less than 10degrees. So there is a sine(10 degrees) multiplication factor too - which is also  small. It ought not to work but, of course, it does.

Skyfall sailing in 3m waves with Hydrovane steering system
Here the hydrovane is steering Skyfall in 25 knots of wind and 3m waves.

I like the hydrovane because it forces you to set your boat up correctly. A prerequisite for success is that the boat, without any external influence(i.e. a wave) or correction from the hydrovane, is set up to sail straight. The sails need to be properly trimmed. You must reef down in time to prevent excessive heel and weather helm. In other words, keep everything in balance. In this case, a very small rudder correction is all that is needed to gain complete control.


The trip from Lanzarote to Cape Verde is the first time we have really tried to use the hydrovane. As we sailed past Fuerteventura I played with the new toy. It would not matter (I thought) if I messed up here, there was no one watching. However, in today's world, Big Brother is never far away. Or in this case Big Sister! Sheila had been following our progress on marinetraffic.com. "Why is your course so wobbly?", she innocently inquired by text.

Skyfall's wobbly track past Fuerteventura
Skyfall's wobbly track past Fuerteventura

I like the hydrovane for it's simplicity and effectiveness. Watching the vane dip from side to side whilst Skyfall responds like an obedient dog, I am in awe of the ingenuity of past generations, unable to utilise modern electronics.


I also like the hydrovane because it requires no electrical power. Although an electronic autopilot is quite efficient with no waves, on  an  ocean passage with wind and swell, it can easily consume 4A. Using the hydrovane means there is circa 100AH less power to generate daily.


But the main reason I like the hydovane is that it provides a backup. Sure, it is not as efficient as a modern autopilot. And you would never use it if you wanted to push for maximum speed. But our electronic autopilot has failed twice in 6 years. If that should happen on a long ocean passage without others on  board to share the handsteering, then life would be tough on the skipper. Now we have a second simple, 'agricultural' system where it is hard to imagine a failure.


Apart from playing with the hydrovane, the passage to Cape Verde has been largely uneventful. We have had all strengths of wind, varying from drifting along in sunshine to hunkered down, sailing with only a reefed genoa. But we managed to eat well, sleep reasonably and Annick's new bucket remains unchristened. Annick is currently writing a post to elaborate further.

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4 Comments


Difficult to relate to what it is to take 16 tons across the oceans, on wind power but steering and mooring on manpower. But is that number a coincidence, or do you refer to old song "You load sixteen tons, what do you get?

Another day older and deeper in debt."

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Tom
Tom
Dec 10, 2022
Replying to

16 tonnes is my estimate fully loaded. Unloaded is 13 tonnes. Then 500l water, 500l diesel, all our gear.. and the wife of course!

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Unknown member
Nov 22, 2022

Thanks for the explanation on hydro-vances. Are we going to get one on wave periods?

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Tom
Tom
Nov 22, 2022
Replying to

I will reply privately on our new understanding. Predictwind now have a model uzing height, inclination, period to predict 'comfort factor'. I know how to use it but am still trying to figure out how it works

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