Design

Most Fibron cables and umbilicals are designed around the requirements of a specific project. Standard components or established construction principles may be used where appropriate, but conductor sizes, hose services, fibre count, reinforcement, protection, buoyancy, diameter, length and terminations can all be adapted to the application. Some diving hoses and cable components are also available in established product ranges.

Early involvement allows the cable architecture to be developed alongside the equipment, deployment system and operating procedure. This can prevent conflicts involving reel capacity, sheave diameter, bending, weight, termination space, power requirements or connector interfaces after other parts of the system have already been fixed. Early collaboration can also identify opportunities to reduce diameter, weight or manufacturing complexity.

Useful information includes the application, operating environment, water depth, required services, voltage, current, fibre count, data requirements, working and breaking loads, required buoyancy, target diameter, length, temperature range and chemical exposure. Fibron should also be given details of the reel, winch, sheaves, deployment method, terminations, connectors, applicable standards and required test documentation.

Not every parameter needs to be known at the enquiry stage. Fibron’s engineers can help identify missing design inputs and areas requiring further definition.

Yes. Reel capacity, drum diameter, fleet angle, sheave diameter, safe working load, heave compensation, deployment tension and vessel footprint can all affect the cable design. Providing this information early allows Fibron to consider bend radius, weight, spooling behaviour, tensile loading and the space available for the complete product and its terminations.

Minimum bend radius is the smallest radius that an umbilical cable can be bent around, without damage. Minimum bend radii are calculated using Fibron’s own design rules that take into account umbilical geometry, construction, materials, static or dynamic state, and tensile loading. They are calculated for static bends (eg fixed bends and one-time bending for deployment or storage) and dynamic bends (due to repetitive flexing, winching or reeling out and in). Fibron’s calculations have been verified through a combination of analysis, testing and years of field experience, to ensure the umbilical’s components are not subjected to excessive strain in service.

Umbilical cables can experience torque and rotation due to external conditions or internal interactions. External conditions such as vessel, ROV or diver motion, waves and ocean currents, seabed movement and vortex-induced vibration can all result in torque applied to an umbilical. Internal torque can be generated by the reaction of umbilical’s helically-wound armour wires to axial loads acting along the umbilical. However, this is avoided in Fibron designs by using more than one layer of wire armour, wound in opposing directions and tailored to create a torque-balanced design, or by using braided fibres as the umbilical’s strength member.

The weight per unit length of an umbilical cable in sea water is calculated by subtracting the weight of the seawater that is displaced by a unit length of umbilical from the weight of a unit length of the umbilical in air. Fibron can apply various design techniques to tailor the buoyancy of an umbilical to suit its application.

A positively buoyant umbilical cable will float in (sea) water because its density is less than the density of the (sea) water. A neutrally buoyant umbilical cable will maintain a constant depth in (sea) water, without sinking or rising, unless acted on by another force, because it has the same density as the (sea) water. A negatively buoyant umbilical cable will sink in (sea) water because its density is greater than the density of the (sea) water.

A kink in an umbilical cable occurs when a loop forms due to some combination of twisting or excessive rotation, with either axial compression or a sudden reduction in tension, which then tightens under subsequent tension. This situation can arise due to issues with handling and installation, snagging, twisting or bending during dynamic operations, accumulated effects of ocean currents and vessel motion, or interactions with the seabed. Fibron can offer various solutions – such as bend restrictors or bend stiffeners – to protect vulnerable points from kinking. Fibron can also advise on handling techniques to minimize the risk of kinking.

Demanding applications – such as ROV umbilicals – often require the use of thin-wall electrical insulation to meet size and weight constraints. In an umbilical cable, thin-wall insulation is a high-performance, reduced-thickness, electrical insulation polymer coating, extruded over electrical cores (copper or aluminium stranded conductors). The polymer is chosen for its electrical performance and thermal resilience, to minimize the thickness of insulation on the electrical core, to optimize the performance, size and weight of the umbilical cable for demanding applications in harsh environments. Fibron has developed the capability to extrude high-quality, thin-walled insulation, underpinned by external verification of its electrical performance.

Optical fibres in umbilicals are installed to decouple them from the forces experienced by the load-bearing elements of the umbilical and its macro deformation. This is typically achieved by the use of Fibre In Metal Tube (FIMT), in which optical fibres are housed in a small-diameter metal tube that is filled with thixotropic gel to damp vibrations and act as a loose buffer to allow the optical fibres to move slightly without breaking. In addition, the radial location and helical lay angle and lay length of the FIMT, within the umbilical lay-up, alleviate bending and axial forces on the FIMT.