Lightweight rope makes deep sea recovery
A salvage operation on a shipwreck 3,200m below the surface of the South Atlantic has been successfully carried out using lightweight ropes made with Dyneema ultra-high molecular weight polyethylene fibre.
Dyneema fiber is manufactured by DSM Dyneema and used by Hampidjan, one of the largest fishing gear and super rope manufacturers in the world, to make Dynex Warp, an advanced patent pending winch line for deep sea lifting and lowering as well as for towing fishing trawls.
The Dynex Warp rope was used over several months on the MV Seabed Worker in a salvage operation to rescue valuable cargo from a sunken ship.
The depth of the wreck meant that use of steel rope would have been virtually impossible, since it would have had a weight in the water of over 35 tons. By contrast, the Dynex Warp rope containing Dyneema fibre weighed only 740 kg, thanks to its relative density of 1.1. Out of the water, 4.2 km of the Dynex Warp rope weighs 6.5 tons, against some 50 tons for the same length of steel rope with the same strength.
This reduced weight affects not only the lifting operation but also the stability of the vessel and its deck load capacity. In fact, the MV Seabed Worker holds a 6,000m long Dynex Warp rope for future operations, doing away with the need to switch to a larger winch requiring a larger and more expensive vessel.
The ship is operated by the Norwegian Seabed Group, a long established company equipped with modern equipment for deep sea operations, including wreck salvage. Over the several months the Dynex Warp rope has been used for the current operation, on a standard drum winch with an electronically controlled spooling system, it experienced no problems at all with the spooling, even though the rope has a high number of layers on the drum.
The version of Dynex Warp used in this operation is a 12 strand braided rope with a diameter of 46 mm. It consists of six different layers that together provide very high cross sectional stability and axial stiffness.
In addition to their extreme strength to weight ratio, ropes containing Dyneema fibre are very durable, with excellent resistance to abrasion and also to weathering. They require very little maintenance, and so help reduce operating costs and increase safety.
