Convert a Mono hull to a Tri?
 

Phil Bolger designed a camp cruiser to use Hobie sail rig and hulls as amams. It is one of his simple plywood square boats. I know the design is complete and has a design number thus should be readily available from PB&F. I think it was featured in Messing Around in Boats, thus there is an essay about the design written by Bolger floating around somewhere.