It should be noted that the model for the Alaska-type breakwater 

 was not built to the correct scale to represent the prototype. Further 

 investigation of the physical properties of the prototype after the 

 model tests were complete revealed that it was heavier than originally 

 predicted. The physical properties used in making the theoretical cal- 

 culations are correct for all the comparisons made in this report. How- 

 ever, care must be exercised in comparing the model test results and the 

 field measurements directly. The physical properties for all the break- 

 waters discussed in this section are in Appendix F. 



The first trough in the transmission coefficient curve results be- 

 cause the wave generated by roll tends to cancel the fixed-body trans- 

 mission. The sway-generated wave is small but cancels a little bit of 

 the heave-generated wave. The total transmitted wave is then almost in 

 phase with the heave-generated wave at a slightly reduced amplitude. 

 Complex interactions among the components of the transmitted wave con- 

 tinue to result in oscillations of the transmission coefficient up 

 through a B/L of 0.9. At values of B/L above this, the transmitted wave 

 is primarily a result of sway motion except for the peak at B/L equal 

 to 1.4 which results from an increase in the fixed-body transmission. 

 Considering the complexity of the breakwater response, the agreement 

 should be considered to be reasonably good. 



(5) Friday Harbor Breakwater . The computed transmission 

 coefficient for the Friday Harbor breakwater is shown in Figure 13. As 

 in the case of the Alaska breakwater calculations, the computations of 

 wave-damping coefficients have been arbitrarily doubled to reduce the 

 excessive calculated motions in the region of resonant motions. In this 

 figure the spacing of data points varies. More points are used to spe- 

 cify the curve in regions of rapid change so that the plotted result 

 accurately represents the theoretical prediction. 



In Figure 13, the first trough in transmission coefficient at about 

 B/L =0.5 results from heave- and roll-generated waves canceling the 

 fixed-body wave transmission. This transmission coefficient is well be- 

 low the transmission coefficient which would be obtained with the break- 

 water rigidly restrained and only fixed-body transmission waves passing 

 through. As B/L increases, there is a peak at about 0.7. At this point 

 the heave-generated wave has almost vanished, and the fixed-body trans- 

 mission is also small. The larger transmission coefficient is primarily 

 the result of a roll-generated wave with a smaller component resulting 

 from sway motion. The next trough at a B/L of 0.9 occurs as the heave 

 motion- generated wave increases and cancels the roll and sway motion- 

 generated components. The fixed-body transmission is very small at B/L 

 of 0.9. As B/L increases beyond 0.9 the transmitted wave is almost 

 totally the result of sway motion of the breakwater. 



At larger B/L ratios there are several oscillations in the 



35 



