In summary,

In high winds you'll want the same sailarea or less with preferably more righting moments. So don't add sail area here. If anything add righting moment = wings

In light winds you'll want more sail area high in the mast. This won't happen with the jib and the I-20 spi is already very large. This means that its area is relatively bit in relation to its luff length. Luff length is more important performance wise then area in a spi. Afterall the 350 sq. ft. Nacra 60 NE spi is not faster then the standard 270 sq. mtr. I-20 spi. So you'll be making costs for hardly any gains. Not smart.


30 inches = 0.76 mtr.
18 lbs = 8 kg => 16 kg in total

Basic I-20 righting moment 150 kg crew = 787 kgm
With wings = 922 kgm = 117 %

With this increase I would just keep the current sailplan and just add wings if you really want that. I big winds you may expect some 5% more speed if the wings don't hit the water etc. Mostly when beating to weather. On downwind legs you won't win much at all.

Wouter