Page 614 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

614 CHAPTER 22 It’s the Little Things That Matter
• HAZMAT spills
• Oil spills
• Potable water tank inspections
All ship hull inspection tasks assume the inspection target is a 600 ft (200 m) oceangoing cargo vessel. Sea conditions assume no current. As the current increases from zero, all ROV systems will trend from their nominal state toward the “X” state. Also, as the length of the vessel to be inspected decreases, all nominal states tend toward the “P” category.
22.1.6.2 Ship hull, pier, mooring, and anchor inspections
In an ideal environment (perfect water clarity, no currents, 360 viewing around the submersible, large powerful ROV system, and vessel at rest), a 100% hull or object coverage could be completed in a relatively short time. Under ideal conditions, the following approach to each inspection task should be considered.
22.1.6.2.1 Ship hull inspections
Approach the 100% coverage ship hull inspection by running a series of inspection lines horizon- tally/longitudinally along the hull. For side hull inspections, start at the surface and descend to the water level where the submersible can still view the surface. Place the submersible in auto depth mode to remain at that level, and run the line from stem to stern (or reverse). Reverse direction, and descend the vehicle to a level where the last line is in sight. Run that line. Continue this method until the hull has been covered to the intersection of the bilge keel (if present). For under- hull inspections, run longitudinal lines, weighting the tether to avoid entanglement of the tether with obstructions on the hull. Continue running longitudinal lines until the hull is covered.
22.1.6.2.2 Pier inspections
Approach the 100% coverage pier and structure inspection on a “voyage in/inspect out” basis. Inspect pilings on a “bay-by-bay” basis. Swim the submersible into the bay and inspect the pilings (progressing outward) as the submersible is coming back out. Start at the surface for the first piling and then run the piling toward the mud line. Proceed on the bottom to the next piling and run it to the surface. Run on the surface to the subsequent piling and repeat.
22.1.6.2.3 Anchor inspections
Approach an anchor inspection from the surface toward the bottom, exercising caution at the lay point as discussed in previous sections of this manual.
Guidelines as conditions deteriorate—for the less than ideal conditions, the following matrix of alternate approaches in varying conditions and situations is provided.
22.1.6.3 Pier inspections
Pier inspections are performed by all sizes of ROV systems. The most efficient method demon- strated for performing pier inspections is with straight pulls into the work site. One bay of pilings should be inspected, and then the submersible should be recovered (or swum out of the piling struc- ture) before performing the next bay. Best results have been achieved by the “look-down and then swim-down” followed by the “look-up and then swim-up” piling scan method. Inspect down on one piling to the bottom, swim to the next, and scan upward toward the surface (Figure 22.8).