Jami,

a full size, strong skeg may of course be built, but then one should take care to close the gap between the boat and the rudder, at least under water (unlike on my sketch).

On the sketch below, I have drawn the skeg so that it also goes up along the transom. Imagine that a full-length flat iron has been bolted to its trailing edge. This could have the gudgeons welded to it. The result would be immensely strong and also help to reduce the gap in front of the rudder.

The shown rudder is not that much bigger than the original, at 0.37 versus 0.31sqm, but the new one has also been moved quite far aft, so together this should increase the turning moment with around 50%.

I would be tempted to fit an endplate both to the rudder and to the new skeg. One thing I noticed when fitting an endplate to Ingeborg-s skeg, last summer, was that it appeared to prevent a build-up of weather helm as Ingeborg heeled over.

Arne

Jami.
As can be seen on that diagram below, the suggested new rudder has a high-stress point around the lowest hinge. I think that can be handled by fitting a metal strap on each side of it. This will be much simpler to make than to make ( a strong enough) skeg to support the rudder lower down.

I could think of two ways of doing it.

• 1.      Rig the rudder as shown on the diagram. Reinstall the original rudder and keep it for the summer. It will serve as a spare rudder. In addition, you can try with the spare-rudder locked or free. If you feel that the boat handles best with it locked, then use it that way. If you find that the boat needs the old rudder to be free for manoeuvrability, then it may be an idea to remove the old rudder next winter.
• 2.      Start the season with the old rudder removed, but with no new skeg added yet. At the end of the season you will know if you should fill in the empty space with a little skeg  -  or if you should re-install the old rudder.

Both my options make it easier to take a step back, than when putting lots of labour in making a structural skeg, meant to support the new rudder.

Anyway, good luck!
Arne

In the self steering gear, the span between bearings is rather small compared with the length of the servo blade, and precision is important to keep the amount of balance area correct. It's not surprising that lashings proved difficult. With rudder lashings at spacings more like half the length of the rudder, and with less need for precision, things should be easier. Going back to Annie's blog entry on 28th May 2020, look at how she filled the holes with epoxy after getting the knots as tight as she could. With the rudder and the skeg glass-sheathed, Dyneema used for the cords and then the lashings stabilised in this way, I don't have concerns about strength and longevity. 

I don't think that making the rudder axis vertical will add much efficiency; it will, however, add some problems of making the structure sound, as you guess.

I wish I had a skeg. Please don't cut yours off, but extend it aft to the transom at the same depth.

Then bond a parallel sided piece of wood, not triangular, to the transom (your 48mm sq spruce will do, but I'd rather use something harder),  long enough to bond to the after end of the extended skeg, so that they give each other mutual support.

Cut away the balance area of the rudder in way of the skeg. Then you can use Annie's figure 8 lashings at deck level and at the bottom of the skeg, for the very best frictional performance (your vane gear will appreciate this).

The draught of the finished rudder should be at least 20cm less than the draught of the keel. You'll be thankful for this when you bounce the boat on a hard bottom. 

If you were to follow David's idea, you could then use Wharram-style rope lacings for the rudder.  I am 100% happy with mine.