Chapter 3 — WIND EQUIPMENT 



Table 3-3.-True Wind Speed From Sea Condition 



Knots 



Sea Conditions 



Probable 

 wave height 

 in feet 



0-1 

 1-3 

 4-6 



7-10 



11-16 

 17-21 



22-27 



28-33 



34-40 



41-47 



48-55 



56-63 



64 

 and over 



Sea smooth and mirrorlike 



Scalelike ripples without foam crests ................... 



Small, short wavelets; crests have a glassy appearance and do not 

 break 



Large wavelets; some crests begin to break; foam of glassy appearance. 

 Occasional white foam crests 



Small waves, becoming longer; fairly frequent white foam crests 



Moderate waves, taking a more pronounced long form; many white 

 foam crests; there may be some spray 



Large waves begin to form; white foam crests are more extensive 

 everywhere; there may be some spray 



Sea heaps up, and white foam from breaking waves begins to be blown 

 in streaks along the direction of the wind; spindrift begins 



Moderately high waves of greater length; edges of crests break into 

 spindrift; foam is blown in well-marked streaks along the direction 

 of the wind 



High waves; dense streaks of foam along the direction of the wind; 

 crests of waves begin to topple, tumble, and roll over; spray may 

 reduce visibility 



Very high waves with long overhanging crests. The resulting foam 

 in great patches is blown in dense white streaks along the direction 

 of the wind. On the whole, the surface of the sea is white in appearance. 

 The tumbling of the sea becomes heavy and shocklike. Visibility 

 is reduced 



Exceptionally high waves that may obscure small and medium -si zed 

 ships. The sea is completely covered with long white patches of 

 foam lying along the direction of the wind. Everywhere the edges 

 of the wave crests are blown into froth. Visibility reduced 



The air is filled with foam and spray. Sea completely white with driving 

 spray; visibility very much reduced 



1/4 



1/2 



2 

 4 



6 



10 



14 



18 

 23 



29 



37 

 45 



3. Winds have just sprung up or increased in 

 speed. 



Some of the factors contributing to an over- 

 estimation of true wind speed are as follows: 



1. A decreasing wind speed. 



2. Waves running into shallower water. 

 MAINTENANCE 



For maintenance procedures for computers 

 refer to chapter two. 



NOTE: Changes to all column numbers and 

 entries on NWSC Form 3140/8 were received too 

 late for inclusion in this manual. Where errors 

 in column numbers appear, refer to the U S 

 Navy Supplement to FMH #1, Chapter 13, Marine 

 Aviation Observations for the most recent ampli- 

 fying instructions. 



49 



