The 48 cm (Drake R13 SL 480mm) fin that came with your board is probably optimum with a 7.5 m2
rig and should work quite well with your 7.0 m2 as well.
For your 8.5 m2 rig I agree with Joe above..... 52-54 cm is probably the optimum.
For your smaller 6.0 m2 sail, 42-44 would be about the best.
Due to the tail width of your 133 Futura, you cannot go too small or you lose alot of performance.
What fins to buy?
Any of the major fin manufacturers have slalom fins, swept pointer fins in this size range, so find one from Select, Lessacher, Deboichet Concept, True Ames, etc at your local surf shop in the correct size.
You can even buy new and used fins online (EBay etc.)
Check with those who sail at where you sail and find out what is working for them, then find a 42 cm (and probably a 52 cm as well) so you can cover your entire sail range.
Hope this helps,
Last edited by Roger; 10th October 2010 at 03:23 AM.