Thanks for suggestions, I'll keep them in my mind and apply soon.
I'll was impressed by the suping of Serenity here http://www.youtube.com/watch?v=6skGtOXKKGk
On the opposite, I was thinking this about upper wind situations.
For venetian boats, that are long and narrow, when someone wants them to
plane with a big engine, used to add some "flaps on the side of the stern.
So, seeing my photos in the most windy situation, with bow up and stern
down, I was wondering if a "semifoil" flat fin like the example in the photo could
work in these situations to change the Serenity from a semiplaning board in
a fully planning one, keeping up the stern, , but still with
all the opportunities in lower winds given by the narrow tail shape...
(also much smaller than the example)
I don't know what was their purpouse, but I've seen some old fins with horizontal flat elements, so they could be a starting point...
Sorry if idea seems too mad, meanwhile I'm recovering from c6-c7 spinal problems so I keep on wondering...