143 



that not more than one -third of the buoy should be exposed: winds of more than 

 20 miles per hour caused excessive tilt if 10 feet or more of the buoy were ex- 

 posed. 



Wave Recorders Used With The Spar Buoy - A pressure recording instrument 

 was developed by the University of California to provide a record of 10 minutes 

 duration. The total length of time scale was about 30 inches, and the pressure 

 scale was about 10 feet per inch, with a total range of 3 inches. A pressure- 

 actuated stylus made the recording by miarking a prepared wax paper located on 

 the periphery of a drum. The drum moved during operation, guided by a helical 

 groove cut into the shaft about which rotation took place. The rate of movement 

 was controlled by a Standard clock mechanism for which the recording drum act- 

 ed as the driving weight. The rate of fall was 1 inch per turn and a total of 5 

 turns was made during the recording period. The linear motion of the stylus 

 was controlled fromi a spring-loaded sylphon bellows exposed directly to varia- 

 tions of the pressure in the water at the level where the instrument was placed. 

 This recorder, called the Mark I Deep Water Wave Recorder, proved to be too 

 delicate, and the records obtained were of insufficient length to provide good 

 sampling for statistical studies. 



The Mark II Deep Water Wave Recorder was then constructed using the 

 component parts of a standard bottom mounted wave recorder for use with the 

 spar buoy system to provide records 3 hours in length. 



Suspended Underwater Pressure Recorders - Disadvantages of the damped 

 spar buoy system were difficulties of installing and retrieving the long line and 

 large component parts. In order to overcome these difficulties, Rauch and 

 Folsom (Rauch, 1945) suggested a scheme for suspending a pressure recorder 

 from a float that would follow the sea surface. The pressure at the suspended 

 recorder would vary as the recorder was raised and lowered in the water by the 

 surface float. If the recorder were to be suspended more than one-half a 

 wave length below the surface, the pressure fluctuation at the recorder would 

 be equal to the water head through which it was raised. If suspended at a less- 

 er depth the sub-surface pressure fluctuations due to wave actions would have to 

 be considered. 



The immersion of the float should be kept constant and the weight of the 

 recorder sufficient to hold the connecting line taut so that the system would 

 operate as a rigid unit. The proper depth for the pressure recording unit would 

 have to be a compromise, since records independent of sub-surface pressure 

 fluctuations require great depths (800 feet or greater for wave periods of about 

 16 seconds), but convenience of handling required as shallow a depth as possi- 

 ble. 



To deternnine the pressure response for various wave periods, a theoret- 

 ical investigation was conducted of the dynamics of the system. The response 

 of the recorder was shown to be a function of the depth of the pressure recorder 

 and the period of the wave. Graphs were developed to convert the pressure 

 recorder reading to surface wave height for various wave periods and instrumient 

 depths. 



Sonic Radio-link Spar Buoy Wave Height Meter (Bureau of Ships, 1948) - Two 

 types of radio-linked spar buoy systems were studied at the U.S. Navy Radio and 

 Sound Laboratories during 1945: (1) a radio-linked buoy that measures the wave 

 height by sonar means and (2) a radio-linked buoy that measures the wave height 

 by a pressure-actuated device. The radio-link was provided to eliminate the 

 need of recovering the instrument to obtain the record. A sonar-type unit was 



