Giant waves, as the old big-wave-riding adage goes, sidestepping the height issue entirely, are measured not in feet but in ‘increments of fear. “California surf journalist Sam George has long been the sport’s most vocal proponent of accuracy in measurement. ‘A wave’s height, like that of a palm tree or an NBA center, is quantifiable,’ he wrote in 1998, signing off with the hope that the surf world would begin to ‘tell it like it is. “Big-wave riders themselves continued to undervalue wave size, but judging panels for big-surf photo contests that require contestants submit photographs of themselves riding giant waves, set about making precise trough-to-crest measurements in order to pick a winner.
Given that Larson was riding a finless wooden surfboard, that a photograph of the second-biggest ridden wave of the period (also surfed by him) shows a swell measuring about 12 feet from trough to crest, and that nobody has ever seen or photographed a wave measuring more than 15 feet at Church, Larson’s estimate – accepted as gospel by surfers in the ’40s and ’50s—can be taken as a magnificent exaggeration. “Underestimating wave size got started in the late 1950s on the North Shore of Oahu, and the practice was widespread by the early ’70s.
Whether playing down wave height as in Hawaii (a three-foot wave would likely be a six-foot wave in California), or ascribing to a “measure from the back instead of the front” mentality, the average surfer’s assessment of wave height is anything but scientific. “As a matter of science, wave height is defined as the average distance between the trough and the crest of all open-ocean waves that pass by a stationary point over a given period of time – one hour for many Internet reports, for example.
Read more here: The Inertia