Chapter 10 — WATCH ROUTINES 



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Figure 10-5. — Illustration of sea waves. 



PERIOD OBSERVATIONS. — The term 

 "period" used in this section refers to the time 

 interval between successive crests. However, 

 there is no such thing as a "period" in an 

 ocean wave record, or in actual ocean waves, 

 because the wave pattern never repeats itself. 

 It should be possible, while watching the waves 

 pass a fixed point, to start a stopwatch at the 

 time that a given crest passes that point and 

 stop it when the next crest goes by. The pro- 

 cedure gives a certain time interval. If enough 

 of these values are recorded and tabulated, the 

 result is a frequency distribution of the so- 

 called periods. 



The best place to observe the time intervals 

 between successive crests of the wave system 

 is from a high point on the ship, such as the 

 deck above the bridge. Look one or two ship 

 lengths ahead to windward. Pick out a mark; 

 for example, a large foam patch, a clump of 

 seaweed, or any other drifting object which 

 is easily seen and at a relatively fixed point 

 on the sea surface. Note the elapsed time in 

 seconds between the moments when the mark 

 is on the crest of the first and last well formed 

 wave in the group. Count the number of wave 

 crests that pass under the mark during the 

 interval. Continue to evaluate the wave sets 



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