Seabed tractor

Lore & Background

The seabed tractor is operated similarly to other remotely operated vehicles, with the operator driving the unit as if on board, using cameras on the unit for visual feedback and other instrumentation. A typical operation involves lowering the tractor onto the seabed over a pipeline once the location is confirmed. The weight of the tractor remains mostly on the gantry, controlled by heave-compensation gear so that only about 40 tonnes rests on the seabed. The position reference of the vessel is then transferred to trim-cube sensors on the tractor's support wires, which should remain vertical. The vessel's position is controlled by the movements of the tractor, with the trim-cube sensors feeding back wire angle data to the dynamic positioning (DP) system, which corrects the vessel's position to keep the tractor wires vertical. The DP system is configured with the center of rotation located on the trencher, allowing heading to be adjusted according to the environment or other constraints.

Reader's Guide

Seabed tractors are notable for their specialized role in submarine cable and pipeline operations, where precise positioning and heavy-duty excavation are required. Their tracked crawler design allows them to operate on the seabed while being remotely controlled from a vessel, with heave-compensation gear ensuring only a portion of their weight rests on the seafloor. The integration of trim-cube sensors and dynamic positioning systems enables the vessel to follow the tractor's movements automatically, maintaining vertical support wires. However, seabed tractors are generally slower and less agile than other ROUVs, and the cable being laid can itself be a hazard if it becomes caught on the umbilical cable. To mitigate this and improve oversight, seabed tractors are sometimes used together with another remotely operated underwater vehicle to enhance the overview and survey progress and performance. Their legacy lies in enabling precise, heavy-duty seabed work that would be difficult or impossible with other vehicle types.

Did You Know?

• Only about 40 tonnes of the tractor's weight rests on the seabed during operation.
• The cable being laid can be a hazard if it gets caught on the umbilical cable.
• Seabed tractors are usually slower and less agile than other ROUVs.