struction of a limited number of these instruments for field tests. 

 The versatility of such simple devices in studying turbulence, fric- 

 tional effects, and periodic variations in currents is immediately 

 apparent. The use of hot thermistors or resistance wires in measur- 

 ing currents also is promising in concept. The cost of experimental 

 models and tests of such devices would be modest. It is recommended 

 that current sensing elements employing thermistors or resistance 

 wires be constructed and tested and that a decision as to further work 

 be based on the results of these tests. 



I. OCEAN WAVE MEASUREMENTS 



The Hydrographic Office has pioneered methods for measuring waves 

 in deep water. However, its experience in measuring waves in shallow 

 water by means of pressure transducers has been limited largely to 

 the Wiancko system and the NOL acoustic system. 



An inverted, narrow-beam echo-sounder used from a submarine 

 produces the most accurate record of deepwater waves. However, the 

 difficulty in obtaining submarines for the purpose limits the practical 

 usefulnes of this method. Until other satisfactory means are developed 

 for recording ocean waves in deep water, full advantage should be taken 

 of opportunities to obtain wave records from submarines. 



None of the other deepwater devices are completely satisfactory. 

 The earliest of these, the floating electric wave staff developed by 

 this Office, is cumbersome and unstable. Experimentation by this 

 Office with the accelerometer wave staff has been only partly success- 

 ful. The shipborne wave recorder of the National Institute of Oceano- 

 graphy, which employs a pressure transducer, has been used exten- 

 sively by others. Its greatest disadvantage is its uncertain response 

 to wave periods less than about seven seconds. Evaluation of the 

 telemetering wave buoy (splashnik) developed by the David Taylor 

 Model Basin is still inconclusive. Certain limitations are evident, 

 however, and it cannot at this time be regarded as a fully adequate 

 deepwater wave instrument. 



Use of an accelerometer as an integral componment offers the great- 

 est promise for deepwater wave measurements from surface ships. 

 However, its use with either a pressure transducer (NIO) or a wave 

 staff (H. O.) is probably not the best combination. Either a high- 

 frequency sonic device or a radar-type instrument for measuring 

 the distance from the prow of a ship to the water directly beneath 

 appears to be the most promising arrangement for fully utilizing the 

 accelerometer for wave measurements. The former seems more 



I- 10 



