Long and skinny powerBoats (BIS)

From http://www.rina.org.uk/showpubl.pl?id=6561&n=560

I have computed hull resistance for Lwl = 65 ft, disp = 30 000 lbs, cp = 0.63, Cm = 0.6, LCB = -2% LCF = -5%
at fn = 0.4 (10.84 kts)
For Bwl = Lwl/6, R = 3425 N.
For Bwl = Lwl/5, R = 3724 N.
For Bwl = Lwl/4, R = 4247 N.

That means a 50% wider boat has only 24% more resistance. equal speed and disp.

More, if you slow down the wider boat to have the same resistance,
the Lwl/6 is 10.84 kts
the Lwl/5 is 10.48 kts
the Lwl/4 is 9.92 kts

The 50 % wider boat has a 9% only speed penalty.

And for the Lwl/5, is it worth to trade 65 sqft of floor space for 1/3 kts ?

The name of the game is not long and narrow, but long and light. Up to the point where the major resistance is not the wave, but the wetted surface. Only at that point, it is interesting to narrow the boat.

For a 9 ft Bwl, (Unsafe analysis, outside of the scope of the regression), R = 3216, or speed with same R would be 11.01 Kts. The trade with the Lwl/5 would now be 1/2 kts (.53) for 130 sqft of floor space. (4 ft wide, 65 ft len)