Thomas G. Lang, Ph.D. is considered by many to be the world's leading authority on SWATH, Small Waterplane Area Twin Hull Ships. Tom holds 8 patents on SWATH innovations.
On July 30, 2015, I visited Tom at home in Solana Beach, California, and he showed me his personal 6 passenger SWATH. It is the first and possibly only PLANING SWATH.
Although SWATHs are not strictly hydrofoils, they do often incorporate small stabilizing horizontal foils in their design.
There are about 50 ships in operation around the world. The largest is the cruise ship Radison Diamond with 375 passengers. The design is said to be the steadiest of all hull designs, except perhaps submerged hydrofoils.
Also shown are some of the few remaining of his hydrofoil kits from his former company Up-right Hydrofoils. About 80 of these kits were sold in the 1960s. Ironically, I was offered a used kit for sale by an acquaintance in Elgin, Illinois, about 1960. At the time I did not have the $300 asked.
Boeing bought a kit and used it on its chase boat for the FRESH 1 jet powered hydrofoil test bed. The US Navy bought one to test in Viet Nam waters during the war.