Figure 13 shows the form in which raw wave data is recorded. Thirty- 

 minute wave records are generally taken every six hours. Records may be 

 recorded directly on magnetic tape also if required. Prior to 5 September 

 1956> 9^ i'~h our records and 19^- 15-minute records have been taken. Waves 

 are primarily due to local winds. Long period swell is very rare. 



5« Underwater Pressure 



Two pressure pickups (Mk IX ) are mounted semipermanently to a guide 

 cable at depths of 20 and 50 feet. Impulses from the pressure pickups 

 are recorded on graphic tape. Pressure records are programmed for 30 

 minutes every 6 hours at fast tape speeds* The remainder of the time they 

 are run at slow tape speeds to record the pressure of the maximum wave 

 heights. The pressure recorders were provided and installed by the Naval 

 Research Laboratory and are of the University of California Mk IX type. 



Figure lk is a pressure record taken at a depth of 20 feet during the 

 passage of hurricane Betsy. The track of Betsy is shown on figure 15. 



6. Tides 



A portable U. S. Coast and Geodetic Survey type tide gage was installed 

 in August at the water level, within the seaward caisson. This gage is 

 only provisional until a remote recording gage is available. 



Approximately 10 days of tide records were obtained in the latter 

 part of August. While the data are not numerous enough to draw definite 

 conclusions, they illustrate the general magnitude of the tidal varia- 

 tions. The mean tide range, 19 August to 29 August, was 3*6 feet. It 

 is interesting to compare this value with the U. S. Coast and Geodetic Survey 

 tide predictions for Georges Shoal Ol°40% 67 01 *5 ? W) corresponding to 

 times of observations. 



Observations Predictions 

 Mean range (22 half cycles) 3.6 ft. 4.6 ft.* 



Ratio (high and low water) *4l* «52~ x ~ 



Time difference (30 highs and lows) -kj min.* -1 hr. 15 min.* 



^Referred to Boston 



Figure 16 illustrates a section of the tide gage chart. 



7. Instrument Mounts 



The original instrument mounts were made of brass and proved to be 

 too weak to withstand prolonged cable vibration and wave action. Similar 

 mounts have been designed for construction in stainless steel which should 

 withstand even the most violent forces. 



