RE: F-type 138 VS Isonic133
Hi Danny L,
Where do you have your mast foot positioned on the FT138?
48 Km/h is 26 knots, and that's not really very fast for off the wind on the FT 138.If you get the mast foot back until the board is almost "tailwaking" I think your speeds (on all points of sail) will improve significantly.
At 80 cm wide, the Isonic 133 would be faster for sure, but again, you must tune the board for the best speed and this usually means having the mast foot a little further back than the middle of the track for a light weight sailor such as yourself.
As far as getting upwind on the Isonic 105, again mast foot tuning, fin size (are you using the smaller or the larger fin?) and technique are all factors.
I'm now sailing the Isonic 101 and find it goes upwind very well "on the fin", but I'm not trying to sail it with anything as big as an 8.5 m2 rig. That's a little "too big" in my opinion. I've sailed it with a 7.5 m2 Retro and 6.6 m2/5.6 m2/and 4.8m2 Huckers, and with these sails it's a little rocket ship, getting upwind (once you get the board up to a speed where the fin starts to work) is no problem at all.
When you are planing fast, on the Isonic 105, check to see where the spray is coming out from under the board.
Most of the white spray should be coming out from under the upwind front footstrap or behind. You should see not appreciable "spray" to leeward and the lee rail should be in pretty much "green" water.
If you don't get the Isonic 105 "up on the fin" it won't be very fast, and you won't get the good lift (upwind) from your fin.
At your weight, if going fast is what you like to do, and giving up a little bit of early planing isn't a problem, upgrading your FT-138 to the Isonic 133 would seem a step in the right direction.
Hope this helps,