deballasting air, breathing gasses, etc. Still 

 others provide information on speed, atti- 

 tude and watertight integrity. In essence, 

 they are extensions of the operator's senses, 

 but the variety and quality of such augmen- 

 tation are a matter of operating philosophy, 

 mission requirements and financial re- 

 sources. 



Operational instruments and devices are 

 categorized by function in Table 10.1. Only a 

 very few vehicles carry all of the instru- 

 ments listed, but at least one and usually 

 several are found on each. The majority of 

 these instruments directly relate to diving 

 safety and also may play a major role in 

 rescue. Consequently, their role in this re- 

 spect is dealt with in Chapter 14, and some 

 reiteration of the following discussion may 

 be found therein. Life support monitoring 

 and control are discussed in the preceding 

 chapter and are not treated further. 



Environmental Information 



Cruising on or near the bottom of the 

 ocean is a task accompanied by many un- 

 knowns. While the location and configuration 

 of major topographic features are generally 

 known, the location or presence of boulders, 

 low escarpments, wrecks and junk is sparse. 

 Therefore, all deep-diving and many shallow- 

 diving submersibles carry devices to provide 

 the operator with ample warning that some- 

 thing is coming into or near his course. It is 

 difficult to judge underwater visibility 

 ranges from submersibles, but 50 to 70 feet 

 under artificial lighting is probably the best 

 one can expect under clear-water conditions 

 and when the lights are fixed to the vehicle. 



In some shallow ocean areas where the 

 water is extremely clear, the natural light 

 visibility range may be two or more times as 

 great. Consequently, devices are provided to 

 extend the ability to "see" beyond the limit 

 of human vision. Not only is this required for 

 safe maneuvering, but it is also a prerequi- 

 site to the search for and location of objects 

 on the sea floor, be they natural or man- 

 made. Long range "viewing" is supplied by 

 sonar or acoustic devices; short range by 

 television and the human eye. 



Sonar: 



Acoustic devices used on submersibles for 

 navigation and search are known by several 

 terms: Obstacle avoidance sonar, avoidance 

 sonar or CTFM (Continuous Transmission 

 Frequency Modulated) sonar. Regardless of 

 its name, its function is to look ahead or to 

 the side of the vehicle and alert the operator 

 to the presence of "things" lying proud of or 

 above the bottom. Two methods are in use: 1) 

 An echo sounder arranged to point forward 

 instead of down; and 2) a sonar capable of 

 scanning a sector up to 360 degrees around 

 the vehicle. Three examples will be dis- 

 cussed: DS-4000's forward-looking echo 

 sounder, Wesmar Scanning Sonar and the 

 Straza Continuous Transmission Frequency 

 Modulated Sonar System. The last two are 

 the commercial brands found most fre- 

 quently on contemporary submersibles. 



Echo Sounder — Mounted on the port side and 

 within the fairing of DS-4000 is a forward- 

 looking transducer electrically coupled with 



TABLE 10.1 OPERATIONAL INSTRUMENTS AND DEVICES 



468 



