Surface and Subsea Positioning for Robson Bight Salvage Johnstone Strait, British Columbia, Canada
In August of 2007, several pieces of heavy forestry equipment were lost from a barge in the Michael Bigg Ecological Preserve in Robson Bight including a lubrication storage cube and a fuel truck carrying 10,000 liters of diesel.
The British Columbia Ministry of the Environment contracted an underwater salvage firm to recover these items, located in over 350 meters of water. This area of Johnstone Strait on the northeast coast of Vancouver Island is a sensitive environmental habitat that is heavily trafficked by resident and transient killer whale pods who feed and come to rub on the pebble beaches. Operations were scheduled for May of 2009, a time when whales were least likely to be in the area.
TerraSond provided surface and sub-sea positioning for the entire recovery project. The salvage barge was mobilized in Vancouver, Canada with an Ultra-Short Baseline (USBL) acoustic positioning system integrated with attitude, heading and GPS positioning sensors. Additionally, an RDI Long Ranger Acoustic Doppler Current Profiler (ADCP) was installed to monitor the strong area currents during operations. The barge was towed to the project location and set in a four-point mooring after the USBL calibration was completed. A Saab Sea Eye Cougar working class ROV was sent to the sea floor to confirm the positions and condition of the wreckage.
The lubrication storage cube containing heavy oils and hydraulic fluid was recovered first, followed by the fuel truck. To prevent a spill during the salvage, a casing was lowered over the truck, guided to the seafloor on cables attached to clump weights. The clearance on either side of the truck was less than one-foot, requiring very accurate positioning of all elements.
Both the lubrication cube and truck were recovered without any loss of diesel fuel. The project was a resounding success, and was hailed by environmental groups and local authorities.