i dont think this is really true... a 115 Hp out board on a 20 ft boat will burn 4.5-6.5 GPH at cruise.... at WOT they will burn 9-10GPH hr max speeds of about 38MPH... a 20 ft inboard Jet with a 350 PFI at WOT burns 11.5 GPH at a max speed of 48MPH.... not that far from each other ... when really looking at it...these are all numbers we have ran on our DTS systems for our boats...
once you start changing pumps and impellors in the jet boats you can pick up a lot more performance...
Jet boats are not the way they used to be....
no matter how you put it, the jet will never have the traction of a prop, making them less efficient.
I've run drag boats off and on for many years, we were playing with adjustable nozzle diameters to help with top end but they still lack the performance of a prop.
All I'm saying is, "a jet boat will burn more fuel then a prop boat."
you can pump out all the #s you want
but i will still run further and faster in my prop boat, for the same amount of fuel.