Weed Fin Size for wide slalom board

Looking to get a weed fin, but not sure of the size equivalency between an upright fin and a weed fin in order to get comparable lift. Hopefully somebody out there sails a similar setup and can give some advice.

103kg intermediate (maybe advanced) rider, sailing 105l Hypersonic (76cm wide) in 15+ knots, mostly with a 6.6 or 7.4. With this setup, the standard 44cm upright fin feels very comfortable - powerful but controlled. Thus, looking for a weedy that performs similarly. Fin box obviously has to be tuttle.

Size or even specific fin recommendations gratefully accepted.

(I have bought a weed fin previously, but it was hopelessly undersized for the board at the time so I don't want to make the same mistake again).

Cheers.

Eckas.

Hi eckas,
I ride hypersonic 105, but am 77kg.
I have a 31cm jp weedy that I use with 7.5 and 6.6. I dont use the drake 34 that came with it and rarely use anything else, only a 60cm if the breeze is under 12 knots.
I find that due to the rails in the boards design (faulty some might say) it wants to go upwind and acts like two side fins at lower speeds, weedy or no weedy. the 31 is an occasional spin out for me but thats a heavy backhand. I have PB on this at 27.88 knots.
This hs105 link might help, look up Bender he is always a good source of knowledge on fins and everything HS105 PM him. www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=39033&SearchTerms=hypersonic,105
oh thats right... I think Lessacher used one of his 28 duo weed and did 32kn with a 7.6m/HS105- he's good to talk to as well. wolfgang.lessacher@t-online.de