Towing: Drawing on the anchor handling experience

For nearly two months, from October to December 2016, two AHTS vessels from the BOURBON fleet, the Bourbon Liberty 212 and 223, carried out two rotations in Nigeria between the Saipem base on shore and a pipe laying vessel for towing equipment: manifolds, pipes, buoys, etc. In addition to technical and maritime issues, this contract required special precautions in terms of safety.

The purpose of the contract entered into by BOURBON and Saipem on behalf of Total was to bring the equipment by barge to the pipe laying vessel, which is preparing for the operation of a new field, about 10 miles south of the Akpo FPSO in Nigeria. Loading was conducted at the Saipem land base, in the Bonny River, on board an 88 meter-long barge. The entire trip down river was accompanied by 3 pusher tugs, which helped with maneuvering through the river bends and provided assistance if needed. A typical operation? After traveling for 24 hours, the convoy stopped and went on stand-by, waiting for the approach procedure and for Saipem teams to be available. The captain conducted a briefing before starting the operation, explaining it point by point to the teams, stressing the risks, particularly when connecting and disconnecting the tow lines, potentially risky operations. "The Liberty 223 maintained the barge's heading, to make it possible to come alongside the barge, and the Liberty 212 kept the barge in a given position," explains Ronan Cloarec, captain of the Bourbon Liberty 212 and AHTS captain for 7 years. "Then, the pipe layer makes the final approach for the last 20 or 30 to come alongside the barge, moving about using dynamic positioning."

The operation is delicate because mooring the barge alongside must be done without a collision, at the risk of damaging the client's vessel. Some cargo weighs over 1,000 t, but the Bourbon Libertys can handle this type of mission with no problem: with powerful winches (80 tons of bollard pull), one winch dedicated to towing, a clear afterdeck, and azimuth thrusters for propulsion, for maximum maneuverability, they are specialist vessels. "It's not an operation we perform regularly, but the experience in anchor handling and towing that we have on board enables us to avoid any technical difficulties in particular: both operations are similar! However, we must stress that communications between the deck, the bridge, the Liberty 223, and the Saipem vessel: that's the key to a successful operation." The weather can also be a risk factor because the wind can quickly pick up to 40 knots, but the proper choice of favorable windows is possible in this season.

Over these 2 months, five cycles of rotations have been successfully carried out, as well as 2 operations to retrieve and tow buoys.

Lastly, the security factor is an important point in Nigeria. To defend against attacks by pirates, any trip down river must take place during the daytime. No armed guards on board, but an escort provided by a local company that accompanies the convoy to the oil & gas field, where another escort takes over.