86 MANUAL OF MARINE METEOROLOGICAL OBSERVATIONS 



9320. DETERMINATION. In general, the wave height should be esti- 

 mated from the best available point on the ship that permits the height of 

 the waves to be compared to the height of the ship. If the observer is free 

 to move about the vessel, the wave height should be determined in accord- 

 ance with the following paragraphs. 



9321. When the wave length is the same as or less than the length of 

 the ship, the height of the waves should be observed and estimated from a 

 low point on the ship, if possible. The point of observation should be chosen 

 amidships, where the pitching of the vessel is at a minimum. The wave 

 height should be estimated when the ship is on an even keel in the following 

 manner: 



9321.1. The height of the waves from trough to crest may be estimated 

 against the side of another ship when in company. 



9321.2. Look over the side and compare the height of waves with known 

 points on the side of the ship. 



9322. When the wave length is greater than the length of the ship, an 

 observation may be made as follows; ^ 



9322.1. When in a trough of a wave and the ship is on even keel, the 

 observer may move up and down (if possible) on the ship's structure until 

 wave crests appear momentarily on a horizontal plain with the height 

 of the eye. The wave height is then equal to the height of the observer's 

 eyes above the water line. 



9322.2. When in company with another ship and the observer's ship is 

 on even keel, determine the amount of the observed ship that is obscured 

 when it is in a trough. The height of the waves may be estimated by 

 judging the size of the ship and the height of her bridge above the water 

 line. 



9323. When both sea and swell or two systems of swell are present at 

 the same time, observations will be more difficult. Estimate the higher 

 system of waves first, then repeat the process for the lower system. 



9400. ENTRIES AND CODING OF WAVE DATA ON WBFORM 615-5 



9410. GENERAL. Two sections are provided for the entry of wave 

 data on Form 615-5; one section (grey in color) is for the entry of "rough" 

 data, the other section (white in color) is for "smooth" data. Each 

 section provides for both sea and swell information. 



9411. When more man one wave system can be distinguished at 

 observation time, the sea wave data will be entered in columns 34-36 and 

 41-43; swell wave information will be e. tered in columns 37-39 and 



