IV. INSTRUMENTS AND DATA 



Most instruments are designed for suspension beneath the lower deck 

 of the tower and are attached to the guide cables. Figure 6 shows a typical 

 arrangement of instruments on the guide cables. The arrangement is flexible 

 and ail instruments are easily lowered and retrieved from the compartment 

 above . 



The guide cable vibration resulting from current and wave motion was 

 one of the principle causes of instrument failure. The amplitude and 

 frequency of these vibrations were not measured! however, on one occasion 

 an instrument mount was dismembered which would require a distortion of 

 at least 3 inches from the plumb line. The fundamental frequency of 

 vibration was not measured but is estimated to be somewhat higher than 

 5 cycles per second. 



As a result of this vibration it has been necessary to employ various 

 means of isolating each instrument from the vibrating cable. 



A summary of the data obtained to date is shown on table III. While 

 much of these data remain in the raw form, efforts are being made to process 

 them to more usable form. These data are available from the Hydrographic 

 Office on a loan basis and in some cases certain processing can be arranged^ 



1. Winds 



The anemometers now in use are Bendix-Friez type AN/UMQ-5B. They 

 automatically record speed and direction and operate continuously while 

 rigged. One anemometer is mounted atop the radio tower 9 175 feet above 

 the sea surface. Two other anemometers are available for lowering beneath 

 the tower at various levels. The latter instruments aj?e mounted to in- 

 strument mounts in an inverted position and are suspended by special rubber 

 bushings to absorb the cable vibrations. Corrosion of these instruments 

 resulting from salt spray is a major problem. Figure 5 shows two anemom- 

 eters being lowered on guide cables. 



While the boundary interference to instruments at the guide cables 

 appears to be small it is detectable under certain conditions. Figure 7 

 shows wind turbulence experienced in the lee of the north caisson, 74 feet 

 away. This turbulence appears to introduce a possible error of i30° when 

 the wind is from the north or the south. There has been no noticeable 

 interference from the east caisson s 152 feet away. Corresponding caisson 

 interference to current and wave measurements has not been detectable with 

 existing instruments » 



2 e Currents 



Roberts radio current meters (Mod. II) are used exclusively. They 

 are lowerable to any depth and record set and drift every hour,, As many 

 as three may be lowered on the same cables to obtain simultaneous data 

 at various depths. 



