Isonic 133 what fin size for sail size.

[Nick F]

Hi, Could anyone please tell me what size of fin I should use for my isonic 133 when using my Tushingham lightning 9.4 and TBird 8m sails.
I am 95kg and power off the fin a lot.
When using the 9.4 sail I used a 48cm fin and found it would not give me much grip, if thats the word I am looking for, but changed it for a 52cm and was better, I don't know if this is due to putting to much pressure on the fin.

Also what size would you recommend for a 6.5 sail ?

Sorry, you have probably heard this question a thousand times before, but would be very grateful for some help and advise.

One more thing, when I bought the board it is for deep tuttle fins, why do you get tuttle fins with it and not deep tuttle.

Thanks

Nick