Don't know much (anything) about the way Yamaha does this, yet friend
of mine has a sea-doo 14', 85HP 'boat'. Since it is a jet drive (like
wave runners) they use *tons* of fuel to stay in the sweet spot (above
4500 RPM). Since there is no torque, you really spin the impeller.

May want to keep this in mind for weekend fuel consumption or the
ability to pull a 210 lb skiier out of the water on one ski.

-jjj