Here's a quote from a reputable source (which I won't name since they may not
like it) that explains it - sort of.

"THe energy associated with the transverse wave system travels at the "group
velocity" of the waves, which equals one-half of the phase velocity in deep
water. The propulsion system of the ship must therefore put additional energy
into the wave syste, to replace that which "falls behind". A nominal
relationship between ship speed and the length of the corresponding transverse
wave may be found by equating the ship velocity with the _celerity_ (phase
velocity) of a small-amplitude gravity wave in deep water,

Vship = Cwave = sqrt( g.Lw/(2.pi)) = 2.26 sqrt(Lw)

where Cwave = celerity or phase velocity of the wave in ft/sec
and Lw = length of the transverse wave in feet.

This can be converted into speeds in knots:

Vs = 1.34.sqrt(Lw) (sorry, no workings shown - trust me)

William Froude first pointed out the practical limiting speed for
surface-displacement ships whe he observed that "the speed with which wave
resistance is accumulating mosr rapidly, is the speed of an ocean wave the
length of which, from crest to crest, is about that of the ship from end to
end" (Froude 1955 p.280) This condition is found by substituting the length of
the ship for the length of the wave, giving a relationship commonly referred to
as the _hull speed_, or critical speed-length ratio:

Vs/sqrt(Ls) = 1.34

end quote

And there you have it.

Steve