The ability to efficiently install subsea modules in increasing water depths is a major condition for the cost-effective development of deep-water oil and gas reserves. The weight of a steel hoisting wire exponentially increases with the working depth and is a significant cost driver for water depths beyond 2,000 metres. The obvious solution is to utilise other types of cable that are not as heavy. Using fibre rope as an alternative to steel wire for deep-water operations is attractive, because its weight is close to being neutrally buoyant. However, the challenges involved with the handling of fibre rope have limited the availability of commercial systems and the application of fibre ropes in offshore installation operations is still not common practice.
Fibre rope is sensitive to internal and external wear, and to the high temperature caused by friction as a result of the rope slipping and bending. Consequently, winch systems designed for steel rope cause the rapid wear of fibre rope. On the other hand, existing systems for the handling of fibre rope are relatively slow, work discontinuously and/or require a complex design and intricate control systems. Developing a new type of fibre-rope handling system – without these drawbacks – requires a knowledge of fibre-rope behaviour and insight into rope-handling system interaction.
In 2010, a joint-industry project was set up to model fibre rope in a finite element study, which simulated the behaviour of the rope during interaction with the handling system. For a comparison between different ropes and handling system concepts, heat generation, dissipation and abrasion are considered as consequences of energy dissipation in this model. A new fibre-rope handling system was developed by selecting the concept with the lowest dissipated energy and optimising the design towards increasing the rope’s lifetime and cost effectiveness.
This project resulted in the design, manufacturing and testing of a 50mT-prototype winch. Factory acceptance tests (FATs) have demonstrated the functional performance. In the second half of 2013, the prototype will be installed on board an offshore construction vessel for further tests at sea.