Image: Mermaid Marine
The vessel pictured above may look like a run-of-the-mill subsea IMR (inspection, maintenance and repair) vessel, however upon delivery to Australian offshore vessel operator Mermaid Marine this October, she and her sister vessel will feature something that no other vessel of its kind has, an active heave compensated offshore crane that utilizes fiber rope rather than wire.
Designed by Deep Tek and built by Jebsen and Jessen Offshore, the crane’s winch has a spooling pattern that allows multiple layers of synthetic fiber rope to be spooled onto the load bearing winch drum with no risk of cutting in. Deep Tek’s engineers worked closely with Lankhorst Ropes and DSM Dyneema to come up with a new rope design with fully optimized fatigue and load bearing characteristics for use in this particular deepwater lowering system.
Deep Tek notes this rope is based on DSM Dyneema’s DM20 XBO fiber and a proprietary coating technology.
Why fiber rope and not steel wire rope?
The answer is simply physics. If you’re working in ultra-deep waters with steel rope, you’re hanging an immense amount of heavy wire off the side of the vessel which will significantly reduce the ability of your crane to deploy heavy objects to the sea floor.
DSM Dyneema’s Segment Manager Offshore, Jorn Boesten notes that for a 70 ton crane operating in 3,000 meters of water depth, its lift capacity is reduced by 34 tons just due to the weight of the steel wire at that depth.
A Dyneema fiber rope is weightless when lowered into the sea which means that whatever weight the crane is rated for, is what it can deploy to ultra deep waters.
Deep Tek says this technology is currently being qualified by DNVGL using Assurance Case methodology, which enables introduction of new technology without relaxing certification requirements.
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