This formula applied to planing boats only and only takes into account the displacement
of the hull, ignoring length. This may seem odd but as opposed to a displacement
hull, the most important factor in determining speed is displacement.
If you think of skipping stones as an analogy, first off a good skipping stone should
be flat so that it can skim (plan) over the water at high speed, secondly it’s
got to be small/light enough so that you can throw it fast enough to allow it to
skim. If that stone isn’t the right shape or don’t throw it right I’ll
break the surface and slow down rapidly. These two characteristics apply to the
The shape of the hull’s run needs to be flat to be conducive to planing (skimming)
and the power to weight ratio needs to be sufficient to get it up on plan.
See Planing Hull for details.