(I hope this belongs here, none in marine eng. forum appeared logical)

   I am in pre-design of a new jet-drive based on an engine which develops full output of 50 Kw (65 hp) at 14,000 rpm.  Before going too far into details, can you say immediately if it is possible (eg for an engineering team) to design / build an impeller which can operate efficiently for a 60 mph craft at this rpm without employing a gearbox to reduce impeller speed?  My prelim. calculations indicate a 16 cm dia enclosed screw with a single progressively pitched flute progressing initially at 2.36 cm / rev on a 5 cm hub and reducing to an outlet diameter of 11.85 cm slipping 33% would produce 100 L/sec of jet.  However I hoped your experience might spot an immediate problem (I suspect either cavitation / power waste problems) or suggest an alternative.
 
    Can it be done?

Thanks