mechanical windvane(selfsteering) how does it work

[johnnyandjebus]

Hello all

As you may tell from my questions below I have never operated a wind vane but do have a question about how it works, idle curiosity nothing more.

I get the principle on how it works;
A wind paddle, at the top of the vane is set so the wind flows equally on both sides. When the boat/wind changes direction the paddle pivots downward causing the oar to rotate via a crank and gear set. The oar(in the water) in a neutral position has water flowing equally on both sides. When it rotates it exposes one side to the water flowing under the hull forcing the oar to rotate to port/starboard. Thru lines connected to both the oar and the tiller the oar's movement to one side forces the tiller in the opposite direction correcting the coarse of the boat.

Ok I get the above, here is what I don't understand, when the oar swings to one side it is out of it's neutral position, in my mind in two ways.
1) the water is not flowing equally on both sides.
2) the oar is not pointing straight downward.

So after the boat has corrected it's course what forces the oar downward so that it is sitting in a vertical fashion?

I understand that the wind paddle returns to a vertical position due to counter weights,which take effect after the paddle has wind flowing on both sides of it equally. This in turn forces the oar to rotate back to it's 1'st nuetral position water flowing on both sides equally.
But the oar returning to vertical? There is no counter weight so why does it return to a vertical position?



Thanks,
John

[GBurton]

The wind vane "air paddle" does not only return to the top (vertical position) It goes past vertical thus turning the paddle the other way in the water causing the oar to return

[ffiill]

In the Hazler pendulum type its a matter of balance.You get boat on course engage windvane neutral/head into the wind;rudder theoretically straight ahead;pendulum oar balanced with equal water flow and vertical-tiller/rudder set for straight ahead.As you drift off track relative to wind, wind vane corrects itself at same time turning the oar like a rudder and putting it out of balance;it regains its balance by swinging at right angles to boat and pressure powers the rudder yokes causing the boat to self steer back on track.Wind vane then settles back into balance corrects the pendulum oar back to straight ahead and in balance.
With some thought you can power up a tiller pilot to replace windvane and take the load off the tiller pilot.

[johnnyandjebus]

thanks for the replies all. It is a interesting piece of equipment to be sure.

John

[GaryHLucas]

John,
The motion of oar is proportional to the angle of the wind vs. the vane. When the boat turns as a result of the oars action on the tiller the angle of the wind is reduced and the oar turns back towards the neutral position as well. In theory a vertical axis vane will steer more accurately, but they don't have the sensitivity to small wind changes. The horizontal axis vanes respond to smaller changes in angle with a larger motion, so are more sensitive, especially down wind.

A really great book, Self-Steering for Sailboats, was written by Gerald Dijkstra and published by Sail Magazine in 1979. I have a copy and you may be able to find one on the internet. WIND-VANE SELF STEERING by Bill Belcher published in 1997 is also quite good, but I like the Dijkstra book better.

Gary H. Lucas

[SvenHee]

Originally Posted by johnnyandjebus

I understand that the wind paddle returns to a vertical position due to counter weights,which take effect after the paddle has wind flowing on both sides of it equally. This in turn forces the oar to rotate back to it's 1'st nuetral position water flowing on both sides equally.
But the oar returning to vertical? There is no counter weight so why does it return to a vertical position?

Thanks,
John

Im am not sure if this applies to all brands but the counter weight on the windvane does not keep the windvane blade up, only the wind does. If the counterweight were heavier than the blade the wind would need to move the extra weight as well as the gear that moves the pendulum rudder. That would mean loss of sensitivity. Maybe brands that have a truly horizontal windvane axis may require a heavier-than-blade counter weight.

But then, how DOES the pendulum go back to neutral?

That is where the servo pendulum is so clever. When the windvane is in neutral, either by wind or because it is locked, the pendulum rudder can still swing sideways.

The transmission that rotates the vertical axis of the pendulum rudder also does this when the pendulum rudder swings out by it self.

When the pendulum rudder swings to one side, the pendulums vertical axis rotates in a way which makes it want to steer back to neutral.

This dynamic stability is what makes a servo pendulum system such a great course keeper.

[johnnyandjebus]

Svenhee

thanks for the above post, it gives more to think about.

John

[Devo49]

The 'paddle' gear you're talking about is the most common type available (Aries, Fleming, Muir etc). This is just one of many types, and I recommend 'Self-steering for Yachts' by Gerard Dijkstra for a comprehensive (in 128 pages!) exploration of this vital subject.
After studying this book ( and John Letcher's effort) I built an auxiliary-rudder steering gear for my 32' sloop, and it works better than any commercial device I have seen. It has a 10% trim-tab controlling a 30% over-balanced rudder, a configuration that gives unparalleled yaw-control, with exquisite sensitivity, on all points of sail, in any wind. Sure, I'm blowing my own trumpet, but (thanks to Mr Dijkstra's advice!), this gear blew me away, from the start.
The very first time I took it out, it was downwind in 5 knots, and she tracked straight and true. Try that with your Aries! Since that first outing I NEVER hand-steer under sail, even on short hops and day-trips. It's so easy to engage, and steers a better course than me, I just sit back and enjoy.
A couple of 'buts': It's permanently in the water (could have made it retractable, but reliability and strength prevailed), and it won't steer under power (the prop-wash plays havoc with the over-balanced rudder).
The rudder is quite small, but very powerful, thanks to the over-balance/trim-tab combination, and handles difficult conditions with ease. Downwind, 40 knots, 15' following seas, I can potter about, tending the fishing-line, make coffee, just relax- this little mother (we call her Sybil, after Basil Fawlty's iron-fisted wife) looks after the steering, and never gets tired, or loses concentration. I do have to watch the trim of the sails, Sybil doesn't like sloppy sailing!
Talking of sail-trim, I'm a great fan of tell-tails: 6" streamers of knitting-wool at 3' intervals about 1' aft of the luff, and 1' fwd of the leach. They let you know when the air-flow over the sail is just right, and max speed is on.