There are apparently several, not just one way, to measure waves. As explained in David Burch's book, <underline>Kayak Navigation</underline>, p. 298, the Canadians publish wave data in a measurement called "significant wave heights." Swell is illustrated on at least some of the canadian charts showing the direction and height of the various components (i.e. a vector which illustrates the swell from the cardinal points about the compass). I could not find an example of these vector diagrams, but I have seen them, I think in the Canadian Sailing Directions (my copy got left in a motel room somewhere). Definition of "SIGNIFICANT WAVE HEIGHT" = The average height of the highest 1/3 of all waves. *********************************************************************** Bascom's _Waves and Beaches_ has tables that include average wave height (H), significant wave height (H3), and H10 wave height, which is the average of the highest 10% of waves. H10 wave height is twice average wave height. In other words, in a typical sea, one out of every ten waves is twice as high as the average wave height. For all of these, wave height is measured from trough to crest. Linda and I were in Canada last week, and the Canadian marine weather reports and forecasts all used significant wave height rather than average wave height, which I think is reasonable -- after all, it is usually the highest waves that cause the most trouble, if only because they are least predictable. NOAA weather buoys also report significant wave heights in addition to average wave heights. Wave height and period are mathematically derived from accelerometer data. FMI, see http://seaboard.ndbc.noaa.gov/wave.shtml. Chuck Holst *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Fri Sep 04 1998 - 10:24:43 PDT
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