Originally Posted by Delfin
My Cape George had a completely unbalanced rudder
as well. I'm afraid I can't remember the exact % of my trim tab, but one thing to remember is that with a wind vane
, you really are not trying to move the rudder a great deal - just enough to stay on course. As a result, you don't need huge amounts of power in the tab, and I found that even my small one generated more than enough. As a guess, I would think that 15% would be fine, and on your vessel a 4 to 5 inch tab should work fine. I would be curious to hear what size Jim Cate's was and whether he agrees.
I sold that boat and vane a decade ago, and all the drawings for the vane are on I-2 in Hobart and I'm in California
for the foreseeable future... hence this is from memory (increasingly untrustworthy these days!).
Anyhow, the tab was about 20% of the rudder width, possibly a bit less. But remember, this was an auxiliary rudder, not the main rudder, and it was semi-balanced. In fact, in the end I kinda reverse-engineered the thing: built the rudder and tab, then adjusted the balance of the rudder to get the response that I wanted. Hanging a tab on an existing main rudder is a different thing entirely.
But, thinking about it a bit, with a longer keel
boat that tracks well, your thoughts that small rudder deflections will be all that is required may well be correct. My boat was an old IOR one-tonner and likely a lot less stable in yaw than an H-28. Again from memory, I would see frequent 10 to 15 degree rudder movements as we sailed along off the wind
. To windward almost no correction was required, so little rudder movement noted. Remember that with an aux rudder you take out any weather helm
with the main rudder and then lock it in place.
Lastly, I don't understand CH's antipathy towards the cable drive systems. The dire friction situations he quotes don't agree with my experience at all, nor the experience of hundreds of AutoHelm
users. And I would sure at least give Dyneema cables
a try... I think that they would be brilliant!