histogram or a regular graph (Fig. 3). The dates of the various wave 

 records ranged from April 1955 to September I96I. 



Extensive use of these wave record spectra has been made for deter- 

 mining estimates of the power spectra for fully- developed seas at various 

 wind speeds and also to develop a new wave-model equation. A group of 

 sjTioptically chosen spectra was analyzed to determine the mean spectra 

 for speeds of 20, 25, 30, 35, and ^1-0 knots. Each situation used was 

 chosen so that both fetch and wind duration would have produced a fully- 

 developed sea condition according to various theories. A nested family 

 of -vrave spectra was obtained for these five wind speeds (Fig. 4) whereby 

 the frequency of the maximum energy was inversely proportional to the 

 wind speed. Also the significant height relationship to the v/ind speed 

 was found to be 



{k) H,^. 0.01«2Vi5.5 



From statistical tests it was further found that wind speed alone at the 

 location and time of the wave condition did not specify the correct sea 

 state. Rather the spectrum was a function of wind duration and fetch as 

 well as wind speed. 



Using the data for the spectra of fully- developed seas at wind speeds 

 from 20 to '^i-O knots a new non-directional wave-spectrum model was devel- 

 oped. Over the most important range of frequencies that define the total 

 variance of a wave spectrum, the proposed spectral model produced a 

 better fit for the range of wind speeds from 20 to kO knots than some 

 previous models (Figs. 5, 6, 7, 8, 9). It was noted, however, that the 

 proposed new spectral model was highly sensitive to wind speed, since 

 only slight variations of speed had large effects on the shape and 

 position of the spectral curve. This spectral model is a compromise 

 among various other proposed spectra and has similar features to many 

 of them. 



The equation for the proposed spectral form is given by 



(5) 3(6J)dW= oL.gl exp[-^(-^J J^^ 



where OC, = 8.10 X 10"3 

 |3= 0.7^ 

 UJ„= — I— — 



V19.5 



Since CL and ^ are dimensionless any consistent set of units can be 

 used in the equation. If wind speed is in knots, frequency in cycles 

 per second and component energy in (ft)2, the equation reduces to 



]) A^(f)df - 0.010707 exp r-63.2L 7df 



This form of the spectral model will undoubtedly need further refinements 

 when additional accurate data become available. 



13 



