Subsea Cable Engineering

Cables have a hard job to do – they have to transmit electrical energy for the life of field, withstanding complex environmental and thermal conditions. Apollo’s combination of practical experience from more than 70 cables projects and 20 offshore wind farms is brought together in a structured and trusted review process, to deliver a rounded assurance on the design suitability.

Cable specifications can be fit for purpose without undue conservatism. Apollo will produce accurate ampacity calculations for the burial conditions, using the latest methods and practical know-how to help optimise costs in the selection of right-sized equipment.

Whether for inter-array or export purposes, optimal cable routing has the same need: secure and optimised paths between the jackets, platforms and landfalls, allowing for the details of seabed soils, geological obstacles, ordinance, shipping risks and environmental conditions. Apollo’s experienced subsea cable team have a range of analytic and data management tools to hand for managing the route design and cable burial definition process. Data is captured in industry standard GIS applications, with clear, focused alignment sheets to efficiently summarise recommendations.

Whether by rock dumping, mattresses, trenching or a combination of the same, practical design solutions are available for stabilising cables on the seabed, with all supporting engineering to relevant codes and standards. Here, Apollo’s experience of the analysis of freespans, sandwave propagation, scour studies and vortex induced vibration (VIV) comes to the fore. We offer workable, focused design solutions for stabilisation of the cable on the seabed, also transition zones and crossings.

Trench profiles and trencher design details can introduce bending stresses, ovalisation and knife edge loading into the product that need to be carefully controlled. Working with our clients we have identified state-of-the-art methods of evaluating these effects and recommending effective mitigation methods. Apollo have the experience and analytic tools to deliver robust assurance that the projects objectives can be achieved with the trenching tools available.

To minimise installation risk, the cable lay vessel requires practically-focused operating envelopes that can be incorporated into procedures. With normal lay, first and second end pull-in, survival, abandonment and recovery operations to consider, a vast number of diffraction analyses and OrcaFlex™ simulations are used to prepare vessel operating envelopes, static lay tables, and hold back guidance. Apollo supports both the contractor and the developer in processing and interpreting this detailed information into workable, uncluttered guidance for offshore teams.

As offshore wind goes into deeper waters, additional challenges can be expected through the deployment and use of dynamic cables between the substructure and the seabed. The historic mechanical damage risk in cable installation work becomes greater when the substructure is floating, adding new degrees of freedom and degradation mechanisms. While dynamic cables are relatively new technology, there is excellent opportunity to transfer learning from other sectors and from the fixed wind installation methods to reduce risk in the configuration. Apollo teams work across multiple sectors and will bring this experience to produce robust, marinized solutions.

Operators of offshore wind farms need to have assurance that their equipment will withstand the long-term effects of the dynamic marine environment. Apollo teams have advised operators and contractors on the integrity risks in their cables and protection systems, considering principal mechanisms of abrasion, wear, impact, corrosion, fatigue and mechanical failure. Often the effects compound one another, and sound, forward thinking mitigation measures are needed. Apollo teams will recommend workable ways of assuring long term performance in the system.