tuoy, which provided point spectra. Datawell supplied a wave slope following buoy, 

 referred to as the WAVEC buoy, and Delft University supplied a low cost, 

 "disposable" acceleration buoy. DTNSRDC supplied a wave orbital following buoy 

 manufactured by ENDECO and designated as the Type 956 Wave-Track. Ship motion and 

 wind were measured by the team from Delft University. 



This wave study provided an opportunity to compare the wave height and 

 directional measuring capabilities of the Wave-Track buoy in relation to the other 

 buoys and the observed data. The Wave-Track approach to directional wave measure- 

 ment is based on a different concept to the conventional slope following method, 

 i.e., the determination of wave directions by sensing the wave orbital velocities. 

 This allows the design of the buoy to be small and lightweight compared to slope 

 following buoys. For trials work, the Navy requires a lightweight, easy-to-handle 

 directional sensing wave buoy that provides a first order measurement of wave 

 directional it ies. 



The ENDECO Wave-Track Buoy gives the U.S. Navy a tool to help validate its 

 spectral wave model. The Spectral Ocean Wave Model (SOWM), operational since 1975 

 at the Fleet Numerical Oceanography Center (FNOC) in Monterey, California, 

 provided forecasts of wave environmental conditions at specified grid points in the 

 Northern Hemisphere every 12 hours. The model permits the simultaneous represen- 

 tation of both locally generated wind seas and swell from decaying or distant 

 storms. The wave model can also be used in a hindcast mode by using historic 

 pressure field data to derive wind and ultimately wave data. Some of the results 

 have been reported in References 2 to 7« 



Within the past year a newer ocean wave model has been used, replacing the 

 SOWM at FNOC. The Global Spectral Ocean Wave Model (GSOWM) provides forecasts of 

 wave data with a finer grid spacing of 2I/2 degrees. The new model still generates 

 forecasts every 12 hours, but now encompasses both the Northern and Southern 

 Hemispheres. 



In addition to its use with SOWM, the directional wave sensing capability of 

 the Wave-Track buoy allows the Navy to apply the measured directional seaway to 

 predicted ship response amplitude operators (RAOs). The developed ship responses 

 can then be compared to trial measurements to help validate predicted RAO 

 values . 



*A complete listing of references is given on page 15. 



