Jami,

If you were starting from zero, the trim tab would be a contender, but ...

Given that you already have a pendulum gear to my design that you say works very well, it seems to me that for the least amount of new work and the most confidence in the end result, you only have to make a new mounting frame that is wide enough and long enough to fit around the new rudder. That avoids stepping into the unknown with the RHM, and probably getting worse performance all round  from the trim tab.

Don't be afraid to tilt the frame up a bit, so that servo blade trails and the vane leans forward a bit - say 2 - 4 degrees. This will make it easier to get the servo blade clear of the rudder.

Of course, if the vane has enough power. It might be helped with a little balance on the trim tab.

And if it doesn’t work, I’ll make a new turret for the vane.

Thanks again.

Thanks David,

but would this still mean that I wouldn't be able to use the wind vane I made using your plans?. It has a 75mm tube as a drum.

Hmm, let's see. Here's the rudder again:

As you can see, there's significant angle aft and even more above the waterline. Here's a better picture of this, let's call it A:

The rudder axle is in a very comfortable position in relation to the solar panel arc, on which I would install the wind vane (like it once was).

But if should make a trim tab along this yellow axle, the "trim tab tiller" would be about 35cm (10cm gap + 25cm)  long to reach the point of the rudder axle. Sounds too much to me, for the horizontal David Tyler -style wind vane to be able to move the tiller enough.

Let's see picture B:

This way the trim tab would sit on a different angle than the trailing edge of the rudder. However, the "trim tab tiller" length would be reduced to 25cm to reach the tiller axle. 

Any ideas on how to proceed, please?

(The yellowish dust you see on the transom and rudder is birch pollen. Today was the worst pollen-day ever. Not a good day to paint the mast... but then again the weather has been changing between rain, rain and cold with little dry days. So I had to paint the mast today. Well, my sail is yellow, so the microscopic yellow dots don't matter that much :D )

The most important things with trim tabs are that the length of the tab tiller has to be correct, relative to what's driving it, and the forward end of it has to be in the correct position, relative to the rudder axis. The angle of the trim tab axis is immaterial.