400 hp Mercury diesel outboard is real!

[Bushwacker]

I bet it can suck some fuel too..

That Allison gas turbine was originally used on the Army's Kiowa helicopter; it's a low compression 1960's vintage design. Merc version doesn't look like it has any heat recovery devices on exhaust, so BSFC is probably 0.7 or higher (a good diesel is about .35). That would translate to a fuel flow, at the 400 hp rating, of over 40 gph! At part power it will be even less efficient!

In the mid 60's, Pratt & Whitney developed a waterjet for use with the 650 hp PT6 gas turbine for use in river patrol boats in Vietnam. They put one in a 32' Formula! My neighbor ran the camera boat they used to get some PR shots of it, a 32' Rybovitch w/twin 500 hp Holman-Moody engines. Said he could just barely stay with it with the throttles firewalled. What impressed him most was that it was almost silent - all he could hear was a slight whistle. He said it did run out of gas pretty quick!

Latest PT6 is rated up to 1200 hp, so you could have some fun with that rig if you could find a water jet that could handle it!