Wind vane/Trim tab self steering

[Mike2309]

This is from a previous discussion -
http://www.diy-wood-boat.com/images/Windvane_axis.jpg
(at least, I hope so - can't seem to paste the image directly into this) It shows 2 control lines . The upper one is clearly for the connection between windvane and trim tab to be made/unmade. But the lower one? is that just to haul the trim tab into the inline (with the rudder) position? If so could not both tab and vane be set free to go their own way, then be locked together once on course? Also what is the notch in the toothed wheel for? Text says it allows the locking lever to drop right through the wheel (when the S/S gear is not in use?) But the control line lifts it up and out of engagement so why not just leave it like that? I'm imagining that to rapidly disengage the S/S you would grab both lines, pull and make fast.
Am I just not understanding the situation?

 

[barnaclephill]

But the lower one? is that just to haul the trim tab into the inline (with the rudder) position? If so could not both tab and vane be set free to go their own way, then be locked together once on course? Also what is the notch in the toothed wheel for? Text says it allows the locking lever to drop right through the wheel (when the S/S gear is not in use?) But the control line lifts it up and out of engagement so why not just leave it like that? I'm imagining that to rapidly disengage the S/S you would grab both lines, pull and make fast.
Am I just not understanding the situation?

Firstly, the picture is not very large or detailed, and mine has a separate paddle (pendulum servo) rather than a trimtab, but..

Mine has 2 lines: one line controls the angle of the vane (aerofoil) and I've made it a continuous loop. The other line goes throug blocks to pull the tiller this way or that.

To rapidly disengage I take the tiller line/chain off the bolt sticking up out of the tiller. I have a tillerline with a short section of chain; the chain sits on a protruding bolt in the tiller. To quickly disengage I lift the chain off the tiller, the tiller is free to move. The trimtab will not be aligned perfectly and will cause some drag, but only momentarily.

The tab and vane cannot be set free to go their own ways directly. The aerofoil will be allowed to rotate to align it with the (apparent) wind while the tab is needed to be in-line with the rudder. Then they're locked together. The aerofoil out of alignment moves the tab which pulls the rudder over, then they come back into equilibrium.

Quote: Text says it allows the locking lever to drop right through the wheel (when the S/S gear is not in use?) Unquote. I've heard of some mechanisms that have the aerofoil free to align then locked into place with a small bolt or locking mechanism. There could be a looped line to align the aerofoil , controlable from closer to the cockpit/companionway, or it could be done manually (albeit leaning over the stern of the yacht.) Then aligned it is locked.

I'm sorry I can only answer part of your question. I am not familiar with the linkage(s) between trimtab and rudder - I'll check

 

[barnaclephill]

trim tabs

Attached are scans from (part of) pages 116 & 118 of Bill Belcher's book "Windvane Self-steering....theory, principles and practice" ISBN 1-877197-00-9 in the chapter of making your own trimtab system.

Picture 1 shows a control line lifting the course-setting disk, whilst picture 2 shows the part where the aerofoil controls the trimtab which produces feedback to the rudder as a whole.

Do these pictures help explain, or could you elaborate with pictures your situation. I could scan more, but more info please..