For your curiosity I learned this from a cuple of books, when I was to write about the subject in college!! I don't think I understod all the tecnical English at first!? SO the main problem with jets, is that they grow less efficient, because of the air getting into the system at high speeds??? Writing this I remember another fast Yacht, The 114' "Gentry Eagle". It was a project to beat the world-reccord cross the atlantic... It actually did in 1992 (62hrs 7min with topspeed of 69.6 knots!!) Nowdays it's refitted to a yacht with topspeed of 63knots. Anyhow this yacht has two V16 Diesels conected to waterjets... but the main powersource for high speeds, it's gasturbine is connected to an Arnesson suface-pearcing drive! Before this I thought a lot of why they used this configuration?. Parhaps it's just to get the power into the water in high speeds then??