Weighing the benefits of fibre rope for offshore lifting operations
August 27, 2020 Maritime Safety News
Oil companies and charterers have implemented tighter cost controls and stricter emissions initiatives to reduce costs and cut CO2 emissions from their offshore operations. This has put added pressure on OSV owners and provided “a strong incentive to use available offshore vessels and equipment for a wider range of operations with only modest modifications,” NOV Rig Technologies product line manager, lifting and handling Ronny Hoff told Offshore Support Journal.
“The cost reduction aspect is perhaps the most tangible driver however, we do see that a documented reduction in emissions is also increasingly a deciding factor,” said Mr Hoff.
He said this was more evident in the offshore renewables market “where the operators are considering the supply chain holistically, including installation and decommissioning in terms of emissions.”
For offshore lifting operations for subsea work, operators traditionally deploy a large subsea vessel equipped with an offshore steel wire active heave compensated crane.
This, however, does not have to be the case, pointed out Mr Hoff. “Fibre rope technology facilitates the use of a smaller vessel and a smaller crane for a given subsea operation, reducing energy consumption and emissions for both the vessel and the crane.”
Hampidjan Offshore director David Waage agreed. “There is a need in the market for fibre rope development to allow the OEM´s to go deeper with existing gear, using smaller cranes and vessels for higher payloads,” said Mr Waage.
Based in Iceland, Hampidjan is a manufacturer of DynIce and DynIce Dux high-performance synthetic ropes for offshore applications.
While synthetic fibre rope has been widely accepted in other applications in the offshore industry for mooring and towing operations, for instance, it has not yet made the same inroads for lifting applications.
“However, these types of rope have not been fit for purpose for typical lifting operations where the rope is spooled on a winch and will be subject to abrasion and wear,” pointed out Mr Hoff. “Steel wire rope, on the other hand, has been used for this application for many years and has been thoroughly vetted. Moving from steel wire rope to a new generation of fibre rope has significant benefits but will also face the challenge of not meeting the same acceptance as the traditional solutions.”
But Mr Hoff noted that the characteristics of fibre rope make it well suited for offshore lifting operations, particularly at greater water depths. Besides its inherent strength, fibre rope is neutrally buoyant, ensuring it will not decrease the deliverable payload of the offshore crane regardless of depth.
By contrast, offshore cranes using steel wire have to bear the load and the weight of the wire paid out.
The reduced weight of the fibre rope as compared with steel wire lowers energy consumption. The lighter weight of the fibre rope means that a smaller crane can be used on a smaller vessel, which have lower day-rates than larger, specialised vessels.
Repairs are also simpler. Repairing damaged sections of the rope, said Mr Hoff, can be handled by splicing. And if the winch capacity allows, fibre rope can also to be lengthened with additional sections.
The nature of fibre rope also enables it to be embedded with fibre optic cable to allow for both rope monitoring and communication to the hook/payload.
Despite these advantages, much like any new technology or application of an existing technology in a new market, fibre rope faces several initial hurdles for widespread adoption in offshore lifting.
Chief among these is that there is less industry experience and market acceptance for offshore lifting applications. Additionally, fibre ropes have a higher capex than steel wire. However, Mr Hoff noted that the increased cost per capacity when purchasing fibre rope was offset by “reduced capacity requirements (the ability to use a smaller crane) and lower day rates of the vessel.”