Weed fin - please advice the length.

[marek]

Hi,

How long should the weed fin be for a 125l/69cm board used with sails
6.4, 7.5 (and 9.0 if possible).
My weight: 200lbs/90kg.
Right now I use 46cm quality freeride fin for all my 3 sails and it
works ok (not 100% perfect, but pretty good).
Is it possible to cover the same range with weed fin?

Thanks,

-marek