today im picking up a new second hand sail, 6.8 north warp, I have a 30cm weed fin and another fin with suggested sail range on the side. is there a table you can copy laminate for your gear bag.
many factors to take into account
board width, volume, weight of sailor, etc
example: for my 8.x sails I use a 48 cm fin on my freeride and 56 cm on my JP SLW freeformula
here is a table from Select fins and there are others
For free ride I always go sail size times 5 plus 2.
e.g
5.0m sail = 5x5 = 25 + 2 = 27cm fin
6.0m sail = 6x5 = 30 + 2 = 32cm fin
Got this tip on a clinic once and works for me every time, I go +/- 1 either way to suit my existing fins.
For slalom I usually go sail size x 5 plus 3.
Not sure about weed fins though.
ok seems to make sense all my fins are 30cm
don't quiet make sense of the graph, may be having a blond moment.
I have a 6.2, 6.5 and 5.4ish sails
According to Maui Fin Company, a lot with width of the board. According to them, we are choosing too small fins lately for our boards width. My friend chatted with them while they were testing fins for Naish boards. Funny however, when i try stock fins, I feel most of the time that I'm over finned!! ;-). They were saying, fins are now so well understood that it's will not spin-out. If you spine-out for no reason, you are under fin.
Tribal Windsurfing.com has a chart which is good to compare. And probably accurate if using their fins
As a guide only as fins will work differently to another style/brand. Wave slalom weed speed
JP has a chart too
@ains :
based on your question ...
i made myself a chart of wind strength with sail size mapped against board with fin:
so, in 20 kph winds (~11 knots) i will use JP SLW92 with 10 m² sail and 66 cm Select slalom or 58 cm True Ames SB weed fin
and i put litres/width as a board indicator as well
you can also see that sails in 8.0-8.5 m² range can have fins from 30 cm to 58 depending on the board !!