Finding boxes lost from Rena wreck
A container is seen on the seabed using the WASSP multibeam system.
A multibeam sonar is being used to good effect by hydrographic surveyors at the grounding site of the 236m cargo vessel MV Rena on the Astrolabe Reef off the coast of New Zealand.
Single beam echo sounders and side scan sonar had been used to support the salvage operation. However multibeam systems provide a more economic means of gathering seabed information, particularly in deeper waters, and have been used to locate lost containers.
WASSP Ltd provided one of its sonar systems for the salvage effort. General manager Ian McDonald pointed out the benefits of the system “In 100m of water, the swath will cover a strip of sea floor 346m wide from port to starboard, 173m either side of the vessel, he said. “In relation to the Rena salvage, WASSP provides a means of covering a lot of seabed very quickly, which is crucial in a salvage operation.”
Certainly speed is of the essence in the Rena salvage attempts, as bad weather and high winds mean that the response has had to back off a number of times. Some 100 containers have been taken off the ship, which now has a large crack down one side, although almost all of the fuel has been removed to minimise the pollution risk. Still there is the problem of a number of containers which have fallen to the bottom of the seabed, with the potential of more to follow.
It helps that with this particular 160kHz multibeam sonar, hydrographic surveyors are able to generate detailed seafloor profiles from 2m to 200m in depth and can accurately locate seafloor structure, shipwrecks and foreign objects in the water column. In fact, within two days of the WASSP manufactured sonar system arriving in Tauranga, it had been used to identify 12 targets, seven of which were submerged containers, some at depths of up to 80m.
The surveyors involved in the salvage effort were able to get the equipment fitted and the system up and running in a very short time frame, most useful considering the nature of the Rena salvage operation. This included the associated Navigator and WASSP Sonar acquisition software.
The company says that fast deployment is partly down to WASSP’s Windows-based software, which is easy to use. All the functions are controlled by a computer mouse.
Also, it will run automatically without requiring continuous operator input. All the data can be exported to a third-party chart plotting system and raw multi-beam sonar information can also be saved for further analysis.
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