Thank you guys for the tips...
I'll try the smaller fins... I actually only changed to a smaller fin once (65cm), and it was 15 knots. I felt so unconfortable and so deep in the water that every time I look at that fin I get dizzy...
I guess it was not used on the proper way.
About the mast foot, I actually, when over 15k, go to maximum set to the nose. I don't know its just a feelling that I perform much better upwind and I it's easier to mantain the trim of the board. When in high winds with my 10sqm sail I fell like could go over 5cm from the mast track!!!!
What do you think about that? Is it to weard for the 147 to use the mast foot so much to the nose?