Man, that looks like fun. I'm glad you posted it here but there is an Iceboat association, BBS, etc. where you could find plans or more info. Although it looks like most of them don't have that outer "boat" shape. I found them on http://www.google.com/advanced_search with "plans" and "iceboat" as key words.

I do everything the hard way but I'd whittle a scale half-model out of wood. There are several books available from Wooden Boat on the subject. You can pull offsets from the half model by cutting it into sections (if I understand it correctly) and measuring each section. When the offset table is complete, use it to draw the waterlines/buttocks out in plan and profile. Use a batten to make sure all the lines are fair (see Alan Vaitses book 'Lofting'). Correct any offset points that don't fall along the batten... then plot/cut out your forms from the corrected offset table and strip as usual.

Good luck and don't forget your seatbelt and helmet

- Chip
http://www.nwlink.com/~chips