were blowing directly on the beam of the breakwater, one would not 

 find the condition of long-crested waves impinging directly on the beam 

 of the breakwater. As a result, the breakwater is not excited uniformly 

 along its entire length. Therefore, the breakwater itself provides 

 restraint against motions which are excited in a local area. The con- 

 struction of this particular breakwater is also quite flexible, which 

 allows for considerable internal damping of the wave-excited motions. 

 The barges tied to the long leg also serve to restrain the motion and 

 provide additional damping. 



There is a strong need, in this case, to provide laboratory data 

 on the breakwater motions, which could be further correlated with the 

 theory and the measured motions. 



If one looks at the measured accelerations by themselves, a consi- 

 derable resemblance in all three degrees of freedom appears. Further, 

 if these accelerations are viewed along with the incident wave spectrum, 

 considerable similarity appears again, suggesting that further investi- 

 gation of the measurement scheme would also be welcome. 



The final comparison to be made is between the theoretically pre- 

 dicted and measured mooring-force coefficient. The theoretical predic- 

 tion and measured data for the seaward mooring line is shown in Figure 

 32. The correlation appears to be quite good in this case. 



In looking at the time series of force on the mooring lines and 

 the windspeed, one can observe a definite correlation between the wind 

 gusts and increases in the mooring force. This is probably a result of 

 the large barges tied to the structure which act almost as sails. If 

 this is the case, the increase in tension caused by the mean wind on the 

 barges needs to be accounted for. No attempt has been made to do this. 



The most common method of presenting the spectral data obtained in 

 the field uses a frequency scale rather than the nondimensional beam/ 

 wavelength scale used in Section II. In this section the comparisons 

 are made using a frequency scale. For the Friday Harbor breakwater 

 (beam = 25 feet) the conversion is: 



L g 

 assuming deepwater waves. 



69 



