Jami,

A trim tab's only advantage is that the vane can be smaller. Otherwise, it has disadvantages - it subtracts from the force of the rudder it's powering, so that rudder has to be bigger; it provides no active yaw resistance, unlike the pendulum. It's more complex than a simple vane-to-aux rudder gear, as complex as a pendulum.

If you want to go for an auxiliary rudder, instead of a pendulum, have a good look at the Hydrovane, which now has a 50 year successful history, and is well respected by voyagers, including Jean-Luc Van Den Heede. See if you can understand the mechanism from the photos. That's difficult, and you won't be able to duplicate it, but look at the general principles. They deliberately don't give too much away in the photos, but it's something like this: A vane which is a cloth-covered frame on an axis inclined at about 15˚ to the horizontal. A vertical push-pull rod. A mechanism to change the vertical motion to rotational motion of the rudder shaft. A rudder that is one third to one half the area of the main rudder, with a balance of about 15%.

What you should be able to manage is a vane with a 15˚ inclined axis, with a drum and a cord drive coming down, out to the corners of the transom and then back to a tiller on a dinghy-style rudder, half the size of your main rudder, with 15% balance, mounted on the transom. You should be able to copy the vane of my pendulum gear.

You may or may not find this easier to make than my pendulum gear, but there won't be much difference. Either should give good steering.

Jami,

I like your idea of shrinking the suggested transom hung rudder into an AUX. rudder for windvane use.
On the sketch below I have drawn in the smaller rudder in blue.  Note how the balance (in %) has been increased to almost 22% to let a large hor.-axis windvane control it directly. The Bill Belcher OGT MkII would be my choice. That model struggled a little with driving my Albin Viggen's rudder, but that rudder was un-balanced. Your setup would be much more windvane-friendly.

Arne

Jami,

The best yard angle is mainly a function of required balance of the sail. As said, my hunch is that your felt improvement stems from moving the sail forward, as well as reducing area. 

If you try with the top panel again, and then shift the sail as far forward as you can, how does the helm balance end up? Remember, a ten degree, or even just a five degree rudder angle is not good for the speed.

My own experience with the three top panels with 70deg. yard, has been very good, both on my present Ingeborg, and on the much more tender Frøken Sørensen.

Arne

When I turbo-charges Malena’s flat sail in 1991 by fitting hinged battens and 10% camber, I soon found the boat to be over-rigged. Before next season, I had permanently rolled up the lowest panel, and the mast was cut down from 9.7 to 8.7m. In addition, the solid spruce pole was planed down 1-2cm (diameter). This turned out to be a big improvement.

In those early days I had no experience with un-stayed masts, so I bet the first version was about 80kg, which was 5.7% of Malena’s displacement. The mast of Ingeborg is less than 2.5% of her displacement  -  so I must have learnt a bit since then.

My guess is that when you have sailed for a while with the top panel removed (SA reduced from 27.3 to 23.0sqm), and with the sail shifted a bit forward, you will like it, and then you can shorten the mast as well, which will improve the boat as it did on my Malena.

Arne

More testing is to follow.

Regarding reefing, I compared the drive with four panels (ie 1-4)  in the original sail and four  panels (2-5) on the experimental one, so no difference in the SA.