OFFSHORE REELS & CABLING
STRAIGHTFORWARD PRAGMATIC APPROACH TO CABLE LOAD-OUT
Project headlines are typically impressive portraying the big picture. Often attention to the detail will be the reason for a successful project execution. Every offshore renewable project will require installation of cabling. However, even before the cable installation vessel or barge casts off there is a critical operation that needs to be carefully managed: the cable load-out.
PLANNING
The considered and detailed approach to planning the load-out operation is appropriate to both a new project as well as to a cable repair situation that will almost certainly be completed in a highly charged and urgent situation. Good planning will ensure the most effective, efficient and low risk load out.
LOAD OUT PROCEDURE
The load-out procedure should prevent any breach of the specified cable design limits during execution. These limits include applied tension, bend radii and external pressure on the sidewalls. It requires the attention of an engineer who understands the practicalities of taking a cable off the quayside and loading it onto the cable lay vessel (CLV) and has the detailed knowledge of the cable design.
POTENTIAL THREATS
The cable encounters a sequence of mechanical devices during load-out that are potential threats. The tensioners, chutes, rollers and the complex challenge of the free span between the quayside and vessel, are the main ones. All the transitions between the various guides with unconstrained sections allowing free cable movement must be considered in advance of the cable getting anywhere near the quay. Contingency plans must also be in place should load-out equipment fail to operate normally.
MECHANICAL ANALYSIS Detailed mechanical analysis used to study the loads on the cable will ensure the optimised load-out procedure with the minimum risk of damaging the cable. Reviewing sections of the cable that are unsupported and preventing axial compression are as important as ensuring the cable cannot be ‘snagged’ on its way to the vessel.
DYNAMIC MODEL
The complete sequence of events can be checked using a representative dynamic analysis model. The features that can be incorporated into this type of dynamic model can include: variable cable load-out speeds, environmental loadings on the CLV and cable, variable friction coefficients for the chutes and rollers, alternative CLV deck layouts, allowable mooring offset for the vessel and varying cable tensions.
RESULTS GUIDANCE
The results of the simulations would be used to generate a practical load-out procedure incorporating an appropriate level of conservatism. Worst case scenarios should be intelligently considered, understanding the overall challenge of transferring the cable from the quay onto the installation vessel.
Specific and useable guidelines should be easily available to the operators as they carry out the load-out. Experience suggests that documents used during the load-out should be understood with no language barrier.
Tony Kenyon BPP Cables
www.windenergynetwork.co.uk
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