I'm wondering whether you have considered a wind
pilot instead? Jim built a home made auxiliary rudder wind vane
, loosely based on the one made by Autohelm
for our Insatiable (the first). That boat had a partially balanced rudder
on a slanting skeg, and the lateral plane aft added by the aux. rudder was a great assist downwind in large seas. She was a Palmer Johnson Standfast 36, probably 10-11 tons in cruising un-trim (;-)). We did tens of thousands of sea miles with it. No power drain. Silent. Ymmv.
on edit: nice boat, probably better sea manners than the PJ; we used to encounter a few, not so many now.