• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
FORECASTING SWELL WAVES
FORECASTING  SURF

Aerographers Mate 1 & C
Page Navigation
  118    119    120    121    122  123  124    125    126    127    128  
periods.  The  actual  formula  for  the  speed  of  the  wave train is C=1.515T where C is the speed of the wave train and T is the wave period in the wave train. All of the different wave trains (series of waves all having the same period and direction of movement) in the fetch can be compared to a group of long distance runners at a track and field meet. At first all of the runners start out at the starting line at the same time. As they continue on, however, the faster runners move ahead and the slower runners begin to fall behind. Thus the  field  of  runners  begins  to  string  out  along  the direction of travel. The wave trains leaving a fetch do the same thing. The stringing out of the various groups of waves is called dispersion. In  a  swell  forecast  problem  it  is  necessary  to determine  what  wave  trains  have  already  passed  the forecast point and which have not yet arrived. After this has been determined, the wave trains that are left are the ones  that  are  at  the  forecast  point  at  the  time  of observation. Angular  Spreading As the wave trains leave the fetch, they may leave at an angle to the main direction of the wind in the fetch. Thus, swell waves may arrive at a forecast point though it may lie to one side of the mainline of direction of the wind. This process of angular spreading is depicted in figure 6-6. The problem in swell forecasting is to determine how much of the swell will reach the forecast point after the  waves  have  spread  out  at  angles.  This  is accomplished by measuring the angles from the leeward edge of the fetch to the forecast point. These angles must  be  measured  as  accurately  as  possible,  figure  6-7, and are determined by the following five rules: 1. Draw the rectangular fetch. Figure 6-6.-Angu1ar spreading. 6-10







Western Governors University

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.