Page 591 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

590 CHAPTER 21 Practical Applications
may require armed escorts. Because ROV operations normally require the operators to focus on the ROV, it is strongly recommended that separate personnel carry out the task of team protection/ security.
21.4.2 Tactics, techniques, and procedures
The capabilities and limitations of the individual ROV systems determine the deployment proce- dures, since the more powerful systems allow for higher distance offset through greater currents than do their less powerful brothers. For the purposes of classifying the procedures, the systems are divided into smaller categories for ease of procedure assignment (as further defined below).
The tactics, techniques, and procedures (TTPs) developed for this text are intended to be manufac- turer nonspecific to prevent these procedures from being tied to any single manufacturer of ROV equip- ment. Techniques were tested on a variety of ROV systems in the small observation class category to validate and gain confidence as to these procedures’ applicability through a range of ROV sizes and capabilities. The systems tested were placed into three general observation class categories based upon their respective sizes, weight, and forward thruster output available. The size assignments were:
• Small: Submersible weight less than 10 lb (5 kg) with forward thruster output less than 10 lb (5 kg)
• Medium: Submersible weight between 10 and 70 lb (5 and 32 kg) with forward thruster output 10
20 lb (5 and 9 kg)
• Large: Submersible weight above 70 lb (32 kg) and/or with forward thruster output greater than 20 lb (9 kg).
21.4.3 Operating characteristics of ROV size categories
The overall size of the system partly determines the payload capacity and ability to carry larger, more powerful thrusters. Thruster output determines the vehicle’s capability to deliver the submersible to a place where it can produce a useful picture while fighting currents and pulling its drag-producing tether. Generally, the larger the submersible, the more powerful the thrusters. Other control, drag, and stability considerations include the hydrodynamics of the thruster placement (affecting laminar/turbulent flow through thruster housings), vehicle stability at higher speeds and, the largest of these considerations, the diameter of the tether (circular shapes having the highest drag coefficient) being pulled behind the vehicle.
To summarize, vehicle size category determines the physical capability to maneuver into a place to accomplish the task. The viewing from that point is a function of camera coverage and distance from the item being inspected. If water clarity is 5 ft (1.5 m), the ROV can be no more than 5 ft (1.5 m) away from the target. The larger the standoff (i.e., water insertion point to work area), the larger the thrust necessary to pull the tether to that workplace. The stronger the current, the larger the thrust required to overcome the parasitic drag created by the vehicle and the tether.
Conversely, while a larger ROV may be able to overcome the above-described obstacles, the larger ROV is heavier, has a larger system footprint, and requires more electrical power (e.g., larger generator with higher fuel consumption and space requirement, louder engine with higher emis- sions). Although the smaller vehicles are more easily affected by the conditions described above,