I used a Navik vane on a 29'' fin keel, spade rudder boat in all conditions and it work endlessly and effortlessly for over 30000 miles. I used twins downwind by hanking on a #3 and poling it out one side and free flying another #3 with pole on the other side. You can sail quite a way off dead down wind by adjusting the poles and if the wind starts to pick up, adding belly,by easing the sheets works as a temporary reef, I also rigged
lines via blocks to the tiller from the individual sheets and I could sail ok with this arrangement. Your steering needs are dictated by the boat first..since most boats handle differently I suggest you look for sister ships and query them for suggestions. If your boat is still in production a call to the company will probally be your best be initally. I would also call or e-mail the various companies that manufacture vanes and solicit there recommendation. Fair Winds