These underwater ranges utilize a number of hydrophones 

 (varying from 5 to over 200) placed on the seafloor in a specific pat- 

 tern. The ranges cover areas which vary from several square miles to as 

 large as 200 square miles. The sound created by any object (or of a pinger 

 attached to an object) within the range is received by these hydrophones 

 at slightly different times, depending on the distance from the object to 

 the particular hydrophone. The resulting electrical impulses are usually 

 carried by underwater cable to a submerged termination chamber. In the 

 termination chamber all signals are gathered, and, in some instances, con- 

 ditioned. From the termination chamber, the data are carried through the 

 surf zone by a smaller number of heavier cables, designed to withstand con- 

 ditions in this most severe transition zone, to shore-based equipment for 

 final conditioning and analysis. 



The underwater termination chambers are usually located in 

 shallow water (60- to 80-foot depths) and are usually larger and heavier 

 than the hydrophone structures which are designed simply to support one 

 or more small hydrophones in a relatively fixed position on the deep-ocean 

 seafloor. The hydrophones are located in water depths from 600 to 12,000 

 feet. Some individual underwater ranges vary in depth by as much as 9,000 

 feet. The hydrophone structures, which are usually identical within each 

 range, have heights from 1 5 to 50 feet, mean lateral dimensions from 4 to 

 50 feet, and submerged weights from 300 to over 1 ,000 pounds. Although 

 the basic nature of these structures is such that relatively small loads are 

 involved, their foundations must still minimize settlement, tilt, and lateral 

 movements. The foundation system in combination with the structure 

 also must be designed for easy installation at a rather precise location. 

 Design life for these systems is in the 5- to 20-year category. Some ranges 

 now in existence are as much as 12 years old; most, however, are more 

 recent. 



A number of foundation types have been utilized to support 

 hydrophone structures. These include (in general chronological order of 

 development and use) deadweight anchors, simple spread footings, multiple 

 spread footings, and ring footings. Designers of earlier systems liberally 

 employed universal joints and buoyancy elements to overcome the effects 

 of differential foundation settlement. In this configuration, ocean-bottom 

 currents can disrupt the performance of the hydrophones and, at one range, 

 the system was modified to use a series of universal joints which were locked 

 after a short period of time (Green, 1969; Daniels, 1969). The larger portions 



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