Care must be taken not to tangle the umbilical with the mooring leg during the inspection. The vehicle must be controlled to descend on one side of the leg by maintaining a particular compass heading during descent. If the other side of the mooring is also inspected on the same dive, the operator must remember the direction of rotation of the vehicle and umbilical around the mooring leg, and reverse the rotation before vehicle recovery.
• Inspection and cleaning of mud, sand, or marine growth accretion on underwater surfaces. A small electrical water jet pump is mounted on the vehicle and a hose with jet nozzle is attached to the vehicle manipulator. Spare wires in the umbilical are used to power the pump. The vehicle is controlled to inspect and then jet away the accretion of material. Direction of the jet is controlled by movement of the manipulator. Some forward thrust may be required when jetting is in progress.
• Deployment of under-ice cable spans. As shown in Figure 2-53, a recovery clip is held in the manipulator jaw of the vehicle. A line is attached to the eye of the clip, routed underneath the vehicle, and attached to the aft lower vehicle frame.
The vehicle is deployed through an ice hole in the ROV shelter and can maneuver
to a target hole up to 1,500 feet away (depending pon the length of the umbilical used with the ROV system).
A ring is lowered from the target hole. The vehicle operator locates the ring, connects it to the recovery clip, and releases the clip from the manipulator. Once released, the hook will drop below the vehicle (attached at the aft ñame).
The vehicle is then maneuvered back to the deployment hole as messenger line is deployed from the target hole. Many combinations are possible to achieve longer distances. For example, a run in the opposite direction can be made and the two messenger lines connected to double the distance of the span.
• Cable/line cutting. For small diameter cables (0.1 inch or less in diameter) and lines (0.25 inch or less in diameter), blades are attached to the manipulator jaws of the vehicle for cutting. For larger diameter cables and lines, a cable/line cutting device is attached to the vehicle manipulator arm or a support frame on the vehicle. Spare conductors in the umbilical can be used to transmit the signal to activate the device.
• Moving and placing (water column and on seafloor). Moving, placing, and recovering objects can be done. However, the vehicle umbilical should not be used to lift the vehicle with loads heavier than 50 pounds. Instead, a line delivered from a recovery reel should be used. Lightweight (less than 50 pounds) or neutrally buoyant objects can be recovered or placed using vehicle propulsion. The vehicle manipulator jaws or release mechanisms attached to the vehicle are used to implement pickup and release.
A heavier object can be fitted with a flotation device to provide neutral buoyancy. Once the ROV delivers the object, the flotation device is released or deflated.
• Diver assistance. ROVs can be used in conjunction with diver operations to provide useful functions including:
- Video observation of the diver/ work area for safety and work quality documentation
- llumination of the work site
- Delivery of messenger lines and small tools
- Backup communication via video/ slate
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