It is not as simple as just adding a mast and some ballast to make an effecient sail boat out of a power vessel. I do believe that some catmarrans can be fairly easily converted with a sort bipod rig, for primarly down wind use. This is much different than changing an existing monohull from power to sail. However when you add a mast, there are compression loads which are transmitted down into the hull, counteracted by upward forces on the forestay and backstays as well as the shrouds. Bulkheads have to be placed so that these loads are properly distributed. Also a sailing hull is different than even an effecient power boat monohull. When a sailboat heels, the waterlines are distorted, however the designer has taken this into account and the helm will remain balanced because of the hull form. If you take many broad buttocked power boats and heel the hull, it will creat a huge weather helm. Also putting a ballasted keel, centerboard or dagger board into an existing hull is a huge undertaking structurally. I built sailboats and always had a yacht designer check any changes I made to a hull, rudder, or rig. It is a very complex undertaking. Bob Austin