For your consideration Scott fellow JRA member David Omnick has developed a mizzen sail self steering system for Minimus ll, his JR Catamaran, and his trailerable Bermudan Mono that is fascinating.

You can read about it here.

There are links in the article to videos of the system in action on his Windrose 18 (5.5m) swing keel monohull. (see picture below)

I particularly like that the system does double duty as an anchor riding sail.

David wrote:

Boats with a spade rudder and no skeg are inherently course unstable. Your boat is, and so is Weaverbird. 

A self steering gear for such boats must add the stability that is missing.

The OGT does not do this. A trim tab does not do this.

[...]Only a servo pendulum gear does a fully reliable job of adding the yaw damping feature that such boats need to make them course stable. [...]

That is why I developed the two pendulum gears for which there are drawings in  https://junkrigassociation.org/members_files > drawings > David's vane gear drawings.

I have to recommend that either you build one of these, or you take the easier option of installing an electric autopilot. For short passages in good weather, the latter should serve reasonably well.

David,

I found your argument convincing. After spending some time sailing down wind in smaller waves I think I finally understand the yawing motion of my boat and why I need some sort of appendage in the water to keep the stern from getting pushed from side to side. 

I have been studying your drawings, reading through your topic here, and building the vane in my head. There is one construction detail that I may not understand correctly.

You wrote this:

• The top part of the servo blade is another piece of strong, stable hardwood, section 63mm x 25mm. It is strong bonded and dowelled to the underwater part of the servo blade. This is assembled from solid pultruded GRP sections: 10mm diameter, rectangular 50mm x 12mm and rectangular 45mm x 6mm, all faired in together to form a foil section.

The "dowelled" part is where I have doubts. Did you drill large holes into both the top section (wood) and the underwater part (GRP) and then use round wood dowels to attach the two sections together? I included an image showing roughly what I am describing. Getting this part 'right' seems important. I expect this is the most stressed joint in the system.

David wrote:I am trying to get into the habit of wearing my inflatable PFD whenever I am out on the boat by myself. I don't find it too uncomfortable to wear. If sailing in rougher weather I will also use the harness attachment. It is so easy to fall off a small boat which does not have any life lines, but having reached the ripe old age of 68, and still wanting to enjoy a few more good years of sailing, and life, I think I would be pretty pissed off with myself if I fell overboard with no PFD, and drowning was imminent, and I could have avoided an untimely end by just wearing my life jacket and harness. 

David,

My inflatable PFD starts to feel heavy on my neck after a couple of hours. That is the only discomfort as long as the weather is not too hot. When it is 90 degrees F, like it has been this week, all those layers of start to feel like a winter coat.

I also have a hard time trusting my inflatable in general. If it does inflate then I am sure it will turn me face up in the water and keep me floating. But if it malfunctions, or gets punctured, then it will weigh me down and make it difficult, or impossible, to swim.

For several years now I have been trying to find a reasonably priced static (foam) PFD with an integral harness. I personally think my static PFD is comfortable and protects me from bumping into things. I am sure that it will float even if it was punctured several times.

The only ones I can find have the tether attachment in the back of the PFD, to be used for lifting or lowering a person during a Search and Rescue operation. I want something that will hold me DOWN in the cockpit and be easy to clip and unclip from the front.

Maybe I will try to hand sew some seat belt webbing around my static PFD.

Scott wrote:

I usually wear my inflatable PFD with an integral harness when I sail any further than the distance I think I can swim. But it is not all that comfortable, tends to snag on the lines sometimes and now that it is August it is just too hot to wear all the time.

I looked into buying a purpose-made harness and tether. The prices reminded me why I don't already have one.

So, I did my best to imitate a simple harness using the thread and seatbelt webbing left over from making my sail. It is not perfect, but it was basically free. It only took me about an hour on the sewing machine to make it. I feel safer wearing it. I hope my feeling is right!

If you can't tie a knot, then tie a lot. That goes for stitching too, right?

I am trying to get into the habit of wearing my inflatable PFD whenever I am out on the boat by myself. I don't find it too uncomfortable to wear. If sailing in rougher weather I will also use the harness attachment. It is so easy to fall off a small boat which does not have any life lines, but having reached the ripe old age of 68, and still wanting to enjoy a few more good years of sailing, and life, I think I would be pretty pissed off with myself if I fell overboard with no PFD, and drowning was imminent, and I could have avoided an untimely end by just wearing my life jacket and harness. 

I should learn to draw :)

actually your drawing is very clear. Being easy to do and better looking than  most freehand (well mine anyway) should encourage its use.