a. The Handbook of Sailing, Bob Bond defines it as "the maximum speed a hull
can achieve without planing" (p 342) and goes on to qualify: "only boats
which can plane, or which have very narrow hulls, can travel faster than
this maximum theoretical speed" (p 327).
b. Colgate's Basic Sailing Theory (p 119) states: "the theoretical speed
beyond which a displacement boat cannot go, usually 1.34" times the root of
waterline line length.
c. Chapman's Piloting (p 217) refers to the root of the wavelength
multiplied by 1.34 and (p 26) refers to the LWL root times 1.34. He calls
this a close approximation and describes this as the point at which there is
no reasonable increase in speed for the hull for a reasonable increase in
power.
So what is reasonable? A fully loaded P-19 is about one ton. Push it with a
8 hp motor and it will reach hull speed and probably not plane. The HP/
weight ratio is 8hp/ton. The Albacore submarine of 1850 tons reached 33
knots with 15,000 shaft horse power. Its length is 210 feet. The hull speed
for it is 19.4 knots. It has the same hp/weight ratio as the Potter. It was
submerged to do this speed, obviously not planing. A torpedo has about the
same length as the P-19 and can, without planing, reach speed in excess of
40 knots submerged.
The old Fletcher class naval destroyers length of 375 feet reached speeds of
35 knots (displacement 3000 tons hp/weight = 20) without planing. In fact
all destroyers exceed the hull speed without planing.
A cataraman with one hull in the water also exceeds hull speed without
planing. (If it was planing it would be going sideways due to lack of keel
effect of hull).
So here are my questions:
What is the precise definition of hull speed?
What is the precision of the hull speed formula? Is it 1.340000 x root
(waterline)?
Is the hull speed formula universal regardless of hull dimensions or the
shape of the bow wave created by the hull?
If the Potter has a "power boat hull" isnt that more suitable for planing?
Food for thought or more argument :)
Jim Nolan