waves at an angle on the bow or quarter 



1. The wave length measured by comparing the dis- 

 tance between two crests with the length of the ship 

 or by streaming a buoyant object astern as described 

 earlier must, in this case, be multiplied by a correc- 

 tion factor to get the true value of the wave length. 

 Observed length X correction factor = true length. 

 This correction factor depends on the relative bearing 

 from which the waves are approaching the ship. The 

 table at the right gives the values for the correction 

 factor for bearings from 005 to 355. 



2. Another method of measuring wave length is pos- 

 sible by using the ship's length and the angle at 

 which the waves are approaching the ship. If you 

 determine the time it takes to pass two consecutive 

 crests and the time it takes for one wave crest to run 

 the length of the ship, the following formula will give 

 you the wave length. 



Time to pass 2 crests X Ship's length X 



Wave length = 



Time for crest to travel ship's 



If you cannot see the wave passing the entire length 

 of the ship, choose any two visible points along the 

 side, for which the distance between is known, and 

 substitute these values in the formula for those in- 

 volving the ship's length. 



waves from abeam: 



1. In this case, determine the period as described 

 on page 6 and calculate the wave length from the 

 equation: 



Wave length = 5.1 (Period)^. 



Correction factor 



length 



WAVE DIREGION 



The direction from which the waves are moving can be best determined by sighting 

 with a pelorus along the crests and then adding or subtracting 90° as appropriate. 

 The ship's heading can also be used as a guide to determining the direction from which 

 the waves are approaching. The higher the observation point the easier it is to deter- 

 mine wave direction. The average of several observations should be used as the reported 

 wave direction. 



