Seems like an SX with no wings is a TheMightyHobie18 with a tall mast. Take a hit for the mast, hit for the sq top, possibly a hit for larger main (not sure)hit for the spin, and a plus for smaller jib. I Don't think you can use the slow number for the sx and work from there. Not enough data to support it. It's a Hobie 18 that is modified. Someone else can do the math. I'm an idea guy, not an engineer