There were plans for adding hydrofoils published in Science and Mechanics Magazine (Feb 1960 issue) and Popular Science (June 1960). These issues occasionally go up for auction on eBay, and there are various places to find old magazines for sale. Mike Stevenson's Back Yard Yacht Club offered plans for a small hydrofoil up until they ran out in 2000, and this was not reprinted. Someone told me that the same plans were published in Argosy Magazine in the early 1970s, but I cannot verify that or cite the specific issue. Grumann Aircraft offered a kit called Sea Wings in the late 1950s, some of which may still be around unused in garages and attics. There is an article about them the The Rudder magazine (Aug 1958 issue).