writing, there has been no quantification to evaluate the current effect on the 

 vaves. The theoretical transformation of the waves is applied in the frequency 

 domain in this analysis. 



During mooring conditions, buoy motions are limited by a mooring cable con- 

 nected to a weight and anchor. The abrupt limiting motion that normally occurs 

 with a synthetic rope is reduced when using an accumulator cable, such as that 

 supplied with the Wave-Track buoy. 



The effects of an accumulator type cable on the motions of a buoy such as the 

 Wave-Track buoy was evaluated using a computer model. Some results of the model, 

 presented by Brainard and Wang-^ , indicate that the maximum difference of the buoy 

 surge and heave motions relative to the wave motion are about 10 percent and 1 per- 

 cent of the wave heights, respectively. Buoy peak-to-peak pitch angles range from 

 1.20 to 1.86 times the double wave slope and depend on current velocity, depth, 

 length of mooring line, wave height and period. There is an indication of a mean 

 pitch angle offset which tends to be greater in stronger currents. This bias, 

 though, can be eliminated in analysis. 



Since the model deals in regular waves, no single correction can adequately be 

 applied to a buoy in random seas. However, these values indicate that the buoy 

 closely follows waves in the heave motion. 



In the future, a comparison of a buoy free-floating and a buoy moored is 

 intended to quantify the effects of a mooring on a buoy in the field under spe- 

 cified conditions. 



CONCLUDING REMARKS 

 The adequate verification of the wave directionality produced by the SOWM, and 

 the application of measured directional spreading to ship motions during sea trials 

 is now possible given the ability to measure the directional spreading of wave 

 energy. A lightweight, easy-to-handle directional wave sensing ENDECO buoy has 

 been employed during dedicated trials and ships of opportunity to measure the sea 

 conditions. The Wave-Track buoy measures the directional aspects of the wave by 

 sensing the orbital velocities, as opposed to the wave slope measured by a conven- 

 tional slope following buoy. The nature of the buoy measurements require that the 

 data be converted into a convention of wave slope directional analysis. Therefore, 

 the analysis as outlined in this report was developed to determine the directional 

 characteristics of ocean waves as measured through the wave orbits. 



22 



