The Piaggio P.7 was built for the 1929 Schneider cup seaplane races.
The idea behind it was to use hydrofoils instead of floats, which add a lot of drag when you're flying. The engine had two clutches, one would engage the boat prop and when you were going fast enough to be up on the hydrofoils, you engaged the other prop and took off. That was the theory any way. The pilot that tried it said there was so much spray coming off the hydrofoils that he could not see where he was going and ended the test. The idea was scrapped, it never flew.