Subsea Cables

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Installation Procedures and Methods

Selection of provisional route

Once the requirement for a cable system has been identified and funds raised to build it, the first thing which happens is that a cable manufacturer and installer is contracted by the cable system parties.

A desk top study is then commissioned which identifies a route and the risks to that route.

Items for consideration would be :-

  • Landing Points, Territorial waters, Contiguous Zones (CZ) and Exclusive Economic Zones (EEZ) i.e. the Maritime Boundaries;
     
  • Cable selection;
     
  • Branching Unit deployments;
     
  • Geopolitics - Contested Areas;
     
  • Burial requirements;
     
  • Whether the cable landings can be made directly or have to be pre-laid;
     
  • Permitting & Fisherman Negotiations; and
     
  • Natural and manmade obstacles/hazards such as weather conditions prevailing, currents, seabed conditions, Mineral and/or Oil & Gas exploration, Pipelines, other submarine cables, areas of environmental concern, conservation area etc.

Obtaining permission from the relevant authorities

When the route has been selected and designed, then the initiation of acquisition of permits for the cable system is undertaken. This will involve engagement with Government Administrations, other seabed users and stakeholders i.e. fisheries, cable owners, pipeline owners, etc.

Full survey of route and its final selection

The purpose of the route survey is to identify a safe route for the cable. Even though the Desk Top Study has identified the potential route, the Route Survey will confirm the assumptions made. The Route Survey comprises:

  • Collection of Bathymetry, geotechnical, sub-bottom and side scan data to support route engineering, cable selection, installation and burial.
     
  • The data is made available for review real-time and thus a final selection of the route can be made. Final route selection will consider identifying the safest and most economical route, will optimize cable selection and route length. Avoidance of any hazards identified during the survey process can be made and cable types to be used will be confirmed. An assessment of seabed conditions is also made at this point for the buried sections of the cable.

Cable laying Operations

Once the route survey is complete and the cable system design is finalised, manufacture of the cable is undertaken. When manufacture of the cable is complete, it is loaded to the cableship for deployment.

At the shore approaches where the cable is landed (the shore end), burial is carried out by divers in the shallow water. If the water is too shallow for the main lay vessel to approach safely, a smaller shallow drafted vessel may be lay used to lay the shore end.

Cable Laying Operations

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The main lay vessel (the cableship) is used to lay the rest of the cable system. In water depths where there are risks due to fishing and other man made activities such as anchoring etc., the cable is generally buried to a target depth of approximately 1 metre.  

The cable is laid to conform to the contours of the seabed to avoid cable lying in suspension. During the cable laying process, the cable is being constantly tested to ensure that no damage has occurred to it.

At the end of the cable lay, a final splice is made to join the cable ends together to make a connection between the cable stations. Final tests are then made to ensure the cable is working correctly.

Cable Laying Video

Notification of cable position to other marine users

Following the cable laying operations, the cable positions will be notified to various administrations such as Hydrographic Offices, the Regulatory Administrations and other seabed users such as fisheries.

 

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