They are a Diesel cycle engine, they run on jet fuel. The big benefit is that they are way more efficient, and their low RPMs means you're going to run a gearbox and can fine tune that to an efficient prop speed.

Just saw that very diagram, I somehow missed that little detail.

The Bugatti is single engine, but with twin counter-rotating propellers driven by a gearbox in the nose.

M.C.72 did its job. It still holds the record for the fastest piston driven seaplane.

L’Hydroptere hydrofoil sailboat, the thing is madness!