InnovOil takes a look at the design of Parkburn’s Deepwater Capstan, a key element of MacGregor’s new series of FiberTrac cranes.
Parkburn Precision Handling Systems is working in partnership with crane-maker MacGregor to build a new fibre rope crane, the FibreTrac 1500, designed to lift a 150-tonne payload to a working depth of 4,000 metres. The FibreTrac 1500 utilises Parkburn’s Deepwater Capstan winch to manage the fibre rope during deployments and recovery of payloads to the ocean floor.
Parkburn’s load-handling systems can be found in many land- and marine-based applications, including oil and gas, renewables and cable lay markets. Examples include winch systems, cable lay engines, tensioners, carousels and diving bell-handling systems.
InnovOil spoke with consultant for Parkburn Sam Bull about the philosophy behind the Deepwater Capstan and what it brings to their collaboration with MacGregor.
“Synthetic fibre rope has long been recognised as offering many advantages over steel wire and chain within the offshore industry and is well established for use in mooring systems, soft slings and general handling ropes. Modern materials can equal or in many cases exceed the performance of steel wire; this coupled with the light weight and ease of handling makes it an obvious choice for the crane market. Up until now there has not been a compact lightweight winch solution that can unlock the potential of fibre rope, especially in active heave compensated crane systems,” Bull said.
Recognising that incumbent drum and traction winch technology was not suitable for the handling of heavy payloads with large long-length ropes, Parkburn set about creating an alternative system and spent significant amounts of time and money on developing their patented Capstan technology.
The first full size unit to be built was a 75-tonne demonstration unit during 2012. This was followed by over three years of testing many ropes and configurations to prove their machine handled properly and limited the fatigue induced within the rope during the lifting and lowering process.
“Being a relatively small company with no experience of building cranes, Parkburn recognised the need to build strong partnerships to commercialise the technology. Fortunately, MacGregor had also recognised the potential of fibre rope cranes and were actively looking for winch solutions, and after an in-depth evaluation of the Capstan technology made the decision to use the Parkburn Deepwater Capstan as the heart for their new series of FibreTrac cranes,” Bull said.
Parkburn’s capstan winch looks totally different to current winch technology, consisting of two drums each with 16 interlocking fingers merged together with precise offsets around the rotational centre line to form a cylinder that creates an elliptical rope path with a natural helix.
“The two machines have independent motors and gearboxes on their respective drive flanges and are synchronised with a centre power shaft running through the core of the winch. The machine is more like a mechanical clock with no moving cams or electronic actuators and only has five major components. The goal was to design a machine that has a high level of reliability and does not rely on someone with a laptop to diagnose any faults,” Bull said.
Recognising that winching long-length fibre ropes at high loads required a different approach to standard winch systems for wire, Parkburn set several ideal design goals to ensure the winching system could maximise the performance of fibre ropes including:
Storing the rope at low constant tension.
De-tensioning and tensioning the rope in small bites over a long section of the rope
Ensuring there are no fleeting forces within the system
The winch goes back to basic geometry: once the horizontal and vertical offsets of the two drums have been set the helix pitch is adjusted by modifying the drum diameters. As the machine rotates, the rope transfers from one drum to the next at top and bottom dead centre. This results in another key advantage of the system over a standard multi-drum traction winch, as the rope never leaves the winch. On a standard two-drum traction winch the rope leaves the one drum to the second as the rope moves through the machine, resulting in the rope straightening and bending, and at high tension generating fatigue.
The difference in the de-tensioning profile on the capstan is achieved by having a discontinuous contact surface with a maximum rope contact on any finger of a 22.5 degree wrap angle, and a fibre rope coefficient of friction of approximately 0.07 against the stainless steel profiled fingers results in less than 4% of de-tensioning per finger, whereas a standard traction winch has a wrap angle of 180 degrees, increasing the level of de-tensioning substantially over a short length of rope and thereby generating far more fatigue.
MacGregor FibreTrac 1500 crane system
Although the capstan is a key component of the crane, there are other important technologies supplied by companies, including Applied Fiber, which supplies the fibre rope socket termination; Lankhorst, which provides the rope; Parkburn, the integrated management system that includes the VisionTek 3D visual monitoring system; DSM, the fibre material and lifetime prediction algorithm, and DNVGL, the overall certifying body.
The use of fibre rope in the winch seriously enhances the crane’s performance and flexibility, offering the ability to deploy the surface payload to full depth with no loss of performance. Another advantage is the reduction of weight.
4,000 metres of 88-mm fibre rope weighs approximately 20 tonnes in air (virtually zero in water), whereas the equivalent wire rope has a self-weight more than 200 tonnes. This reduction also has an impact on the speed of deployment and recovery, which affects the efficiency of the vessel, a key driver in today’s competitive market. To deliver 150 tonnes into 4,000 metres of water using a standard steel wire crane would require at least a 400-tonne crane. This has a significant impact on the type and size of vessel that can be used, adding further to the total cost of ownership reduction by changing to fibre.
The crane will be certified under the new DNVGL-ST-E407 specifically designed to cover Deepwater Deployment and Recovery Systems (DDRS). The certification process has been designed to help the process of introducing new technology to industry by moving from the traditional prescriptive approach to one using “claim, evidence and argument approach” to assure the system or individual subsystem is fit for purpose.
A key element of the assurance case is the management of the lift line. Parkburn has developed a robust approach to capturing the work the lift line experiences. The integrated lift line management system captures all the crane’s basic machine parameters in a flexible database. The rope is divided into one-metre virtual segments and the software assigns the relevant data to the corresponding segment of the rope. This data can then be used to calculate the residual life within the rope, which is supported by the 3D visual monitoring system that compares the “as-new rope” to its current condition.
“There are many other applications for this winch technology, including miniature to very large machines, either for cranes or deck-based systems. Parkburn has also tested the use of multiple ropes on one machine; this is useful for overcoming the inefficiencies of very large ropes,” Bull said.
The winch and all the subcomponents have been delivered to MacGregor and are currently being integrated into the FibreTrac 1500, with the crane scheduled to be completed during September followed by extensive testing and certification during the autumn period at MacGregor’s facility in Kristiansand, Norway.