Stepped hydroplanes? Aeronautical work on flying boats and multi-
stepped hulls suggest power economy concerns at takeoff speed and some
intermediate speed transitions.

The hull speed equation is only one indicator.

Hull shape is important. A displacement hull will likely go faster,
further and cheaper than a planing hull at certain speed / power
combinations. it's finesse, I think, as opposed to fine-nese, though
hobie owners report incredible speeds with knife shaped hulls. It's
all about pushing an equal mass of water aside while climbing on top
of it before it can move. It's delta-vee, rocket science versus
frictional area, versus disturbances in the water (wakes) left behind
by hurried boaters.

Think about a nice sailing boat bumkin sliding down a pushing wave as
opposed to a water sucking vacuum behind a square transom. It costs
gas to keep a hole in the water charmed for a long time.

Include ball bearings made of air in there, and you are coming to
grips with most of the problem. The transition to wing in ram air
ground effect is particularly interesting, hovercraft like.

I'd like to see exhaust gas used as friction reduction near the
planing surface of a waterfoil wing almost airborne, almost
cavitating, in ground effect.

A water jet intake at the front could effect certain things, like
elimination of wake in a steady speed submarine. Would leaving a
bubbly, cavitated wake be more stealthy to a satellite looking for
large area reflective patterns on clear days?

Take a look at power / weight / speed curves with reference across all
hull forms at the surface.

Terry K