Deployment Procedures and Cable Hook-up

Green Marine use Orcaflex to carry out cable analyses including developing procedures and lay tables for use offshore during the deployment or recovery of a cable. These analyses are tailored to the site and environmental conditions and the deployment vessel.

Project Natick

As part of Microsoft’s Project Natick Green Marine were responsible for installing a 125m cable extension to an existing subsea cable. This was carried out with Green Marine’s MultiCat Green Isle. In a separate operation, the Natick device was taken to site, the cable extension was recovered and connected to the device.

In order to safely recover the existing cable and lay the extension, a lay table was developed using Orcaflex to co-ordinate the position of the vessel and the length of cable recovered/deployed. Lay tables ensure that at every stage of the recovery the cable tension is known and can be kept within tolerable limits. Exceeding these limits can result in the cable failing. The engineering team developed tables for each step of the cable handling operations.

A separate Orcaflex analysis was carried out to investigate the loads during the deployment of the connector which joined the device cable tail to the pre-laid cable extension. The engineering team developed a procedure which ensured that no twists were created between the cables during the lowering of the device.


SME Warness Decommissioning

Sustainable Marine Energy contracted Green Marine to carry out decommissioning of their test site in Orkney. This scope included recovered of their subsea cable and installation of a test head on the site export cable.

In order to ensure that the export cable was always within its tension limit and minimum bend radius, Green Marine carried out a cable analysis. The purpose of this was to generate a lay table for use during the recovery, splicing of the test head and laying of the test head of the seabed. This was important as the cable was located on a tidal site and during the operation, it would experience tidal speeds of up to 3.0 m/s.

This tidal load makes it difficult to judge the departure angle from the vessel as it can pull the cable suspended in the water column beneath or away from the vessel. With the lay table in place, the vessel crew were able to successfully carry out the operation without any excess stress to the cable.