Underwater work is work done underwater, generally by divers during diving operations, but includes work done underwater by remotely operated vehicles and crewed submersibles.
Skills commonly used by all professional diving occupations
Underwater navigation
Pilotage involves navigation by naturally observable landmarks and phenomena, such as sunlight, water movement, bottom composition (for example, sand ripples run parallel to the direction of the wave front, which tends to run parallel to the shore), bottom contour and noise. Although natural navigation is taught on courses, developing the skills is generally more a matter of experience.[1]
Compass navigation is a matter of training, practice and familiarity with the use of underwater compasses, combined with various techniques for reckoning distance underwater, including kick cycles (one complete upward and downward sweep of a kick), time, and occasionally by actual measurement, which may involve the length of umbilical deployed. Kick cycles depend on the diver's finning technique and equipment, but are generally more reliable than time, which is critically dependent on speed. Techniques for direct measurement also vary, from the use of calibrated distance lines or surveyor's tape measures, to a mechanism like an impeller log, to pacing off the distance along the bottom with the arms.[2]
Use of a guide line or jackstay. A guide line may be laid to facilitate navigation to and from the underwater workplace. This allows divers to travel to and from the workplace with minimal delay, even in poor visibility. A jackstay serves the same purpose in heavy duty format.
Underwater searches
Underwater searches are procedures to find a known or suspected target object or objects in a specified search area under water. They may be carried out underwater by divers, crewed submersibles, remotely operated underwater vehicles, or autonomous underwater vehicles, or from the surface by other agents, including surface vessels, aircraft and cadaver dogs.
A search method attempts to provide full coverage of the search area. This is greatly influenced by the width of the sweep which largely depends on the method used to detect the target. For divers in conditions of zero visibility this is as far as the diver can feel with his hands while proceeding along the pattern. When visibility is better, it depends on the distance at which the target can be seen from the pattern, or detected by sonar or magnetic field anomalies. In all cases the search pattern should completely cover the search area without excessive redundancy or missed areas. Overlap is needed to compensate for inaccuracy and sensor error, and may be necessary to avoid gaps in some patterns.
Diver searches:
Circular search
Pendulum search
Jackstay searches
Snag-line search
Compass searches
Spiral box search
Compass grid search
Ladder search
Swim-line search
Directed search
Towed search
Searches using hand held submersible sonar transponders
Current drift search
Depth contour search
Searches by submersibles, remotely operated vehicles and autonomous underwater vehicles
Inspection of underwater structures, installations, and sites is a common diving activity, applicable to planning, installation, and maintenance phases, but the required skills are often specific to the application. Much use is made of video and still photographic evidence, and live video to allow direction of the inspection work by the supervisor and topside specialists. Inspections may also involve surface preparation, often by cleaning, and non-destructive testing. Tactile inspection may be appropriate where visibility is poor.[3][4][5]
Skills specific to specialist occupations
Underwater oxy-arc cuttingUnderwater fillet weld in a training pool
Erecting formwork (shuttering) and reinforcing steel for casting concrete. (civils)
Non-destructive testing by measuring electrical current
Rigging
Hull scrubbing
Removing a small propeller
Removing sediment with a suction pump
Filling a lift bag
References
^UK Divers (October 16, 2007). "Underwater Navigation". UKDivers.net. Archived from the original on March 13, 2016. Retrieved 2016-05-16. Navigation by reference to terrain features, both natural and artificial, usually with the aid of an appropriate chart.
^Scully, Reg (April 2013). "Topic 7: Underwater Navigation". CMAS-ISA Three Star Diver Theoretical Manual (1st ed.). Pretoria: CMAS-Instructors South Africa. ISBN 978-0-620-57025-1.
^Bayliss, Mel; Short, David; Bax, Mary (17 March 1988). Underwater Inspection. Taylor and Francis. p. 229. ISBN 9780419135401.
Underwater construction training
Industrial inspection
Inspecting a thruster grating
Core-drilling coral
Lifting bags
Placing concrete underwater
Inspecting an intake grating
ROV working on a subsea structure
Salvage work
Ultrasonic testing
Non-destructive testing by measuring electrical current
Rigging
Hull scrubbing
Removing a small propeller
Removing sediment with a suction pump
Filling a lift bag
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