Modifying a water jet for passages (Different design point)

[MechaNik]

I am not looking for variable geometry water jet or any such nonsense or permanently changing the set-up.

What I am asking is if it is possible to temporarily set up a sprint vessels water jet system to perform better on a long passage, hopefully with only minor changes to inlet and outlet diameters. The design point was around 55 knots but for a passage 18 knots on the plane or 10 knots displacement speed would be needed.

Propulsion efficiencies where calculated to be 28% at 10knots and 35% at 20knots so it would seem there is room for improvement, but not that it's realistic.

I assumed that more inlet flow would be needed and the only idea I could come up with is a removable moulded skirt on the inlet duct lip (slight scoop)?

[baeckmo]

Might be possible, depending on "as built" status. Send me a mail with all relevant info on hull, engines and jets; i'll see what can be done without a complete rebuild.