A hydrofoil is a boat which can travel partly out of the water on a pair of flat parts like wings. You can also refer to the flat parts as hydrofoils.
hydrofoil in British English
(ˈhaɪdrəˌfɔɪl)
noun
1.
a fast light vessel the hull of which is raised out of the water on one or more pairs of fixed vanes
2.
any of these vanes
hydrofoil in American English
(ˈhaɪdrəˌfɔɪl)
noun
1.
any of the winglike structures attached to the hull of some watercraft: at a certain speed the hull is lifted above the water and the craft skims along on the hydrofoils at great speeds