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I am constructing an autonomous, unmanned boat for voyages of several months. Traditional autopilots use a linear actuator to move the tiller but require several adjustments per minute. They will consume a lot of electricity and probably wear out mid-voyage. We are looking at wind-vane designs to steer the boat. Wind-vanes are able to steer for great distances without adjustment. The boat will be approx. 5m in length.

In the image below, the 'Course Setting' is done by manually rotating the wind-vane and dropping a pin to hold this position of the two discs. We need a way to rotate the vane fairly precisely and then lock it into position. We are using 12V DC. After it is locked, it should draw no power.

aux rudder trim tab

As you can see, the current design (not our drawing) would have any electromechanical mechanism hanging off of the end of the boat and attached to the rod of the trim tab.

Is there anything we can use to turn and then lock the wind vane in place? Preferably something that could be proofed against wind and water.

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I am going to suggest that you use a worm-drive linear actuator. This will allow you to have a linear movement that does your adjustment and then holds that adjustment when power is removed.

If you can't use a linear actuator, you might have to build something yourself. Regardless of how you do is, I'd still suggest that you use a worm gear system. These can be made to be self-locking when the motor is turned off.

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  • $\begingroup$ I may go a different direction and add a tab to the back of the wind-vane. I can move the tab back and forth by attaching two Bowden cables. I have these cables running back to a linear actuator so I can push and pull them at the same time. As the linear actuator has a worm-screw, it will lock in place without power. Hopefully, I can get the fine control needed to position the wind-vane at the right angle of attack to the apparent wind and the added benefits of very little extra weight added to the rudder assembly and having the actuator attached the hull where it is easier to waterproof $\endgroup$ – Joseph Geddes Feb 21 '15 at 2:22
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One problem with the windvane pictured above is that it might require continous 360 degrees rotation around its mounting vertical axis, e.g. the case boat navigates in circles and/or wind direction rotates 360 degrees.

Otherwise the boat loses the advantage of having a wingsail being able to continously rotate in either direction.

That results in twisting of the bowden cable(s) when the actuator isnt mounted onto the windvane assembly, or twisting of the electric cables to the actuator when it does.

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  • $\begingroup$ Because the trim tab on the rudder only moves a maximum of 50 degrees, then the wind vane should not need to rotate 360 degrees. It should be limited to how much it can rotate - which removes the problem of the the twisting Bowden cables. The problem is sailing at different points to the wind. I will avoid 'dead downwind', as the boat is faster through the water on a 'broad reach', but this still means that the wind-vane is pushed over to one side. Hmmm... $\endgroup$ – Joseph Geddes Feb 26 '15 at 1:44
  • $\begingroup$ the rudder tab yes but the windvane should keep its wind-tracking while the boat turns. And wind can turn 180 degrees then another 180 to a full 360. The windvane should follow this possible rotation, resulting from any combination of boat course and wind changes $\endgroup$ – Cezar T Mar 1 '15 at 8:00
  • $\begingroup$ the bowden cable in itself is sufficient one, not two, since it can push and pull. Airplane models use a solid wire in a tube. I'd worry more about its friction in light winds, and any possible failures from salt water getting in its tube. $\endgroup$ – Cezar T Mar 1 '15 at 8:06
  • $\begingroup$ I started a model for a horizontal axis wind vane. The way these work - by pushing and pulling a vertical shaft allows this shaft to be articulated so its upper part can rotate 360 in horizontal plane while the lower part doesnt. This lower part articulates to a bell crank arm to change force direction horizontally, towards the trim tab arm. $\endgroup$ – Cezar T Mar 1 '15 at 8:26
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I believe the simplest modification to the drawing that meets the requirements is to replace the top disk in the coupler with a standard spur gear. Replace the bottom disk with a worm gear engaged with the upper gear. This would allow the top to be rotated to the desired position, while the bottom only would rotate small amounts so you wouldn't have to worry about twisted cables.

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