When hull speed is reached, a naval architecture of planing hulls pdf in pure displacement mode will appear trapped in a trough behind its very large bow wave. From a technical perspective, at hull speed the bow and stern waves interfere constructively, creating relatively large waves, and thus a relatively large value of wave drag.
Though the term “hull speed” seems to suggest that it is some sort of “speed limit” for a boat, in fact drag for a displacement hull increases smoothly and at an increasing rate with speed as hull speed is approached and exceeded, often with no noticeable inflection at hull speed. The concept of hull speed is not used in modern naval architecture, where considerations of speed-length ratio or Froude number are considered more helpful. As a ship moves in the water, it creates standing waves that oppose its movement. This effect increases dramatically in full-formed hulls at a Froude number of about 0.
This trend of increase in wave-making resistance continues up to a Froude Number of about 0. Froude number of about 0. This very sharp rise in resistance at around a speed-length ratio of 1. 5 probably seemed insurmountable in early sailing ships and so became an apparent barrier.