I will post pics of the cockpit asap. Perhaps, of course, the answer is to enhance the power of the rudder. And that may eventually come to pass .....
Meanwhile, however, I was looking for an easier solution, perhaps only in the short term. Even with full rudder on, my boat will round-up before she is anywhere near rail-down: but if I simultaneously use the auxiliary rudder on the Hydrovane, the boat will hold here course.
That suggests to me that the present under-hull spade rudder is underpowered. I thought that a tiller might improve things in two ways. First, it would allow a much faster response from the helmsman. Second, it could be linked to lines to the short Hydrovane rudder - but, as I say in my original posting, any new tiller to the main rudder could only be 32 inches long, because in the middle of the cockpit is a turret, on which are mounted the engine controls, and inside of which are the hydraulic lines for the steering.
Directional downwind stability in a boat is an immense blessing, and anything else is a curse! Right now, my boat is at the curse end of that spectrum, and I want to fix it.
By the way, there is an emergency tiller on the boat, which is even shorter that 32 inches and a sloppy and loose slip-on (and slip-off) to the stock. I don't have any faith in it, for some reason - but I will give it a try in light weather, an see what happens. And I do remember just how well La Chica's rudder was improved .....