3.51 SMB METHOD FOR PREDICTING WAVES IN DEEP WATER 



Revisions of earlier SMB forecasting curves are seen in Figures 3-15 

 and 3-16. The curves represent dimensional plots from the empirical 

 equations. 



^ 

 U^ 



= 0.283 tanh 



0.0125 



0.42 



(3-21) 



2nU 



= 1.20 tanh 



0.077 



'gF 



,0.25 



(3-22) 



and. 



U 



= Kexp 



B In 



^ 



+ D b 





(3-23) 



where 



exp (x) = 



In 

 K 

 A 

 B 

 C 



loge 

 6.5882 



0.0161 



0.3692 



2.2024 



and 



D = 0.8798 



With these relationships, the significant wave height H^, and significant 

 wave period T^, at the end of a fetch may be estimated when wind speed, 

 fetch length, and duration of wind over the fetch are given. Estimation 

 of wind parameters is discussed in Section 3.4, Wind Information Needed 

 for Wave Prediction, following the evaluation of simplified prediction 

 techniques. In using Figures 3-15 or 3-16 the estimated wind velocity U, 

 the fetch length F, and the estimated wind duration t, when a fetch 

 first appears on a weather chart, are tabulated. Figure 3-15 or 3-16 is 

 then entered with the value of U, using the scale on the left if U is 

 in knots, or the scale on the right if U is in statute miles per hour. 

 This U line is then followed from the left side of the graph across to 

 its intersection with the fetch length or F line, or the duration t 

 line, whichever comes first. 



3-35 



