Green Marine were awarded the contract to be the principal marine contractor for Microsoft’s project NATICK. This involved; extensive operational planning and document creation; assembly of the device at the quayside; loadout and device installation on site; device recovery following the deployment period; preparation for transport and dismantling of the device frame.
Engineering
As part of the planning stage a cable lay analysis was carried out. The primary reason for performing this was to establish a procedure for laying cable while ensuring that it would not exceed any of its limiting properties. For this analysis the Green Marine naval architects used a software package from Orcina called Orcaflex. The analysis covered the recovery of an existing subsea cable, jointing and deployment of a second cable, and recovery and connection of the second cable to a third cable.
Hydrodynamic analyses of the device and the deployment vessel was also carried out. This was modelled using Morrison elements and properties derived from DNV GL recommendations. This analysis was then incorporated into a larger model which included the lift rigging and the GM700 gantry barge used for deployment. The device was transported semi-submerged as this was found to increase damping acting on the device and in-turn reduce the relative motions between the device and the gantry barge.
A variety of environmental conditions (significant wave height [Hs], wave peak period [Tp], wave direction [B], tow speed & simulation origin) were established as inputs. From this, worst-case scenarios were found for varying parameters (rigging loads, accelerations, proximity of device to gantry barge, cable bend radius, tow speed).
Operations
The primary stage of the operations comprised of assembling the device on the quayside. This included working with the local authorities to gain approval and permits for a defined worksite; scheduling equipment/device deliveries; co-ordinating subcontractors; as well as the day-to-day management of the site.
Following the successful cable splice operation and device assembly, the device was transferred onto the GM1100 flattop barge prior to being lifted by the GM700 gantry barge. Device testing was carried out and the GM700 was towed to site with the device suspended from the lift rigging. Once on site the barge was connected to pre-laid moorings and the subsea cable was recovered to the deck. This cable was connected to the device and (following final checks) the device was lowered to the seabed and released. An ROV was deployed at all major stages to monitor key events.
Following the successful 2 year test period Green Marine used the GM700 to recover the device. The device was transferred to the GM700 and separated into the capsule and the frame. The capsule was lifted onto transport for further analysis, while Green Marine dismantled the frame onshore.
