Overall resistance rises as a higher power because it is the sum of
friction, which rises somewhat less that the square of velocity, and
wave making resisitance, which rises as somewhat more than the square
of resistance.


Nav wrote:
Yes, but usually the skin friction is low compared to wave making until
you start to plane...

Sure, it's the nature of exponential functions. Skin frictiongets pretty
big but wave-making resistance is almost vertical around "hull speed."

Have you seen Frank Bethwaite's graphs of hull drag? He worked for a
long time to smooth out the hump in the drag curve when the hull starts
planing.


Yes, and there's a lot of design in controlling wave making scale
factors (until you get to a very long thin hull).

It's all fairly well understood by now. As I understand it, the issue is
to decide on a speed-length ratio you want (basing that desicion on the
characteristics that come with it) and draw a hull with a prismatic that
matches the desired S/L R. Oddly enough (or it least it seemed
counterintuitive to me) higher prismatics go with higher S/L Rs.



Now let's see you explain prismatic coefficient and all it's
ramifications!


The prismatic coefficient (Cp) is the ratio of the immersed volume to to
the area of the midsection times LWL. A big Cp means full ends and a
small Cp fine ends. The coefficient should exclude appendages, bulges
and deep keels.

OK, is that clear to everybody?
Maybe it's just me, but Cp seems like one of those things that just
cannot be understood without a good drawing.

... The ramifications would require a book!

Several books... big ones... and they're inventing new wrinkles all the
time. It's part of what makes naval architecture fun.

DSK