Reliable lue as urexdents of wave height , H, are so diffi- 

 cult that, In general, the reported values represent crude 

 estimates. The height of a large wave is estimated as the 

 eye height of the observer above the water line when the 

 ship Is on even keel In the trough of the wave, provided 

 that the observer sees the crest of the wave coincide v;lth 

 the horizon. The height of a small v/ave Is estimated dir- 

 ectly, using the dimensions of the ship for comparison. 

 On board a small ship the height of waves which are more 

 than twice as long as the ship can be recorded by a micro- 

 barograph. 



The wave period , T, can be measured by recording the 

 time interval between successive appearances (on a wave 

 crest) of a well-defined patch of foam at a considerable 

 distance from the ship. In order to obtain a reliable 

 value, observations should be made for several minutes and 

 averaged . 



The wave length , L, can be estimated by comparing the 

 ship's length with the distance between two successive 

 crests. This procedure leads to uncertain results, however, 

 because it is often difficult to locate both crests relative 

 to the ship and because of disturbance caused by the move- 

 ment of the ship. 



The ve'locity of the wave , _C, can be found by recording 

 the time needed for the wave to run a measured distance 

 along the side of the ship and by applying a correction for 

 the ship' s speed . 



13 



