cemented to a curved surface. Inside the staff and between each 

 contact stem Is placed an appropriate resistance in series. As a 

 wave rises up the staff, submerging additional contact points, 

 proportionately more current flows through the circuit as the 

 parallel salt water current path reduces the resistance of the 

 gage. The upper 12 -foot section of the staff containing the 

 electrical circuit is coated with neoprene rubber. This causes 

 water to drain off the surface of the staff when a wave has passed 

 and prevents current leakage. As an additional protection, a coat 

 of wax polish is applied to the gage section. 2 



The cable to the power source and the recorder on shipboard 

 runs down the outside of, and is secured to, the lower two sections 

 of the staff. From the lower end of the staff, a 7£>-foot cable 

 runs to a life -ring float on the surface and from there to the 

 ship via additional rings as needed (every 100 feet or so) to 

 prevent any additional weight from bearing on the staff. A light 

 line runs to the ship from the edge of the damping disk for re- 

 trieving purposes. In operation it is necessary to pay out cable 

 and line to keep them slack as the ship and buoy drift apart, 

 continuing to keep the cable and line slack until at least a 

 7-minute record is obtained. This is considered the minimum 

 time required to obtain an adequate sample of the waves present. 

 A tautness of the line or cable will upset the staff. 



The shipboard equipment (figure 3) consists of a transformer j 

 rectifier and filter circuitj and a Brush, s in gls -channel, magnetic 

 pen recorder. Included also is a 1-rpm synchronous motor interrupter 

 for placing minute marks on the chart paper. The gage operates on 

 about IS volts a„c, depending on the salinity of the water. The 

 current is rectified and filtered before going to the recorder, 

 which operates on d.c. current. An increase in current in the circuit 

 causes an increased deflection of the pen arm of the recorder. 



Figure h is a sample of the wave trace on the chart paper. The 

 present method of analysis is that described by Warner (19k7) and 

 is used by the Beach Erosion Board. It consists of finding the 

 average period of the dominant waves present and dividing the total 

 observation time by this value to obtain the total number of waves 

 of a given period which could occur in the observation time. This 

 total number is divided by 3 and the highest JftJS* "fffo.^ waves 

 are averaged using a calibration scale. The scale > shows the 

 corresponding pen deflection for gage submergence and is for all 

 practical purposes linear. This value is taken as the "apparent 

 significant, wave height." 



Figure $ shows the dynamic calibration curve for the |pO-Foot 

 Spar Buoy Damping Disk System, which is used for correcting the 

 apparent height values obtained from the trace for the vertical 



2 Recent modifications in the electrical section of the gage can be 

 found in the Appendix. 



