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Old 17-07-2008, 03:59   #1
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tiller pilot with wind steering

Hi all.
I am building in a servo pendulum wind steering system.
The drive comes back through the lazarette wall to a quadrant. The servo angle push rod also comes back there. I want to use a tiller pilot to drive the steering using the servo,s power. I am sure it will all work except.....will a tiller pilot with its in built fluxgate compass work reliably below a steel deck? I have talked to people who have used a fluxgate compass mounted below decks,...but would love to hear from anybody who has operated a ST 1000 or the simrod version below decks. I would love this to be possible because my old tiller pilot dosnt like water !!! It would also make changing from wind to auto very easy. Effectively dropping one linkage off and attaching the other. Any ideas ?


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Old 17-07-2008, 06:53   #2
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The trouble is that the wind pilot relies heavily on a balanced helm. The pendulum exerts a small force on a well balanced helm. You trim the sails properly and it takes almost nothing to hold the point of sail. The course alters to the trim of the sails and the wind direction. If you use a fluxgate compass and the wind shifts you need a lot more power because you are tied to a compass heading and eventually the boat over powers the pendulum and you need a powered servo.

So it comes down to the issue of the servo is unable to counter prevailing wind and sail trim at some point. Connecting the two does not buy you much but maybe just a little tiny bit. The wind pilot really does not need the servo and the added force of the pendulum won't counter act the sail trim leaving the brute force to the servo. If the servo could do the job you would not require the pendulum since it adds so little force.

If the system did work then you would have invented a free lunch since making a low powered servo into a large powered servo can't be done with a pendulum. Both systems work and have value but linking them is not required.

Mounting the tiller pilot below deck is another engineering issue. The leverage afforded is really the only problem and you can compute the force difference of a cockpit mounted version vs. your plan. Make the lever arm equal and the power will be the same but never any better. Being below deck of course solves the water problem. I don't see the linkages being common as saving you anything. The wind vane requires a very low force and the servo is set up to deliver a much larger force. Anything that actually worked might be nothing more than coincidence.

Second is the location of the fluxgate compass. They can be particular about where they operate and metal effects the calibration. With the compass contained inside the unit and not located in the cockpit you have to roll the dice about the location. Being able to locate the compass any place would be ideal. You'll find out when you attempt to calibrate the compass. With enough interference it will refuse to calibrate the magnetic variations caused by the boat and be useless. It will just come down to if it works.

Our last boat had the compass mounted in a poor location that in theory should have been perfect - but it was not. Moving the compass fixed the problem. It was in a forward locker where no metal was located and we moved it aft to where there was a lot of metal. Magnetic fields are what they are. I would say you can't know unless you tried. Steel decks would make me think against it but maybe not. An external compass would make it work as they do work on steel tug boats. That much I do know for sure. I just don't know where they put the compass.

Paul Blais
s/v Bright Eyes Gozzard 36
37 15.7 N 76 28.9 W
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Old 17-07-2008, 08:31   #3
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I have only used a ST1000 in a timber boat but I did have a ST3000 in a steel boat many years ago. The fluxgate and controls are similar between these two units - at least they were 20 years ago. In the ST300, the fluxgate was mounted in the control head which I had mounted inside the companion way - effectively putting the it inside the steel cabin.

What was interesting was when I closed the steel companionway hatch, I could get up to 90 degree heading shift. The amount of shift was very dependant on the initial heading. On some headings the change was hardy noticeable while on others, the autohelm would go hard over as soon as the hatch was closed (or conversly opened if the unit had been operating with the hatch closed).

Quite disconserting, I soon learnt never to open or shut the companionway hatch while the ST3000 was engaged.

From my background experience of aircraft fluxgates, I would tread carefully if considering placing a fluxgate below decks on a steel boat - just take a "suck it and see" approach.
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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Old 31-12-2008, 11:24   #4
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Does anybody have specs on building a wind autopilot?
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Old 03-01-2009, 10:32   #5
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I found a good website for the servo. If anyone is interested.
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