Installing undersea networks and ocean observatories: The CSnet Offshore Communications Backbone (OCB)

This paper discusses the steps key to successful installation of complex seafloor communication, power and sensor networks. Emphasis on a systems engineering approach to design, development and deployment requiring the coordination of a diverse team of optical fiber specialists, marine cable engineers, technicians, deck hands, riggers, ROV operators, ship's crew and officers is essential to safely and efficiently install these systems at thousands of meters of ocean depth. This is illustrated through the detailed description of a system recently installed in the Eastern Mediterranean Sea. CSnet's Offshore Communication Backbone (OCB) will initially serve as the Tsunami Warning and Early Response system of Cyprus (TWERC). Nascent hydrocarbon exploration has also recently begun in this region. As this activity increases, leading to drilling and production, this OCB will similarly be expanded. In a phased approach, the TWERC will be extended to also service this offshore energy enterprise, supporting environmental and well monitoring sensors and providing two way broadband communications and power from seafloor to shore. The initial installation was completed in two preliminary phases. The first phase utilized two vessels (a cable ship and a DP II support ship), each equipped with remotely operated vehicles (ROVs), to lay a total of 255 km of cable, five seafloor nodes, an anchor interface and a seawater ground anode. Both multi-beam and visual (ROV) pre-deployment seafloor surveys of each node (junction box) site was performed. Installing each node, connectivity was maintained (power and communications) with the deployment vessel enabling its functionality to be continuously monitored while being lowered through the water column and after its touchdown on the seafloor. The second phase of this OCB installation deployed a moored buoy that provides both power and communication to the TWERC, in advance of any eventual shore-ended cable and power station and the attendant permitting required for such an installation. This phase required three surface vessels and an ROV to deploy the anchor, the buoy itself and nearly 2.4 km of riser cable with its associated buoyancy modules. Upon their installation, buoy and mooring were “plugged” into the anchor and anchor interface via ROV wet mate connectors (WMCs). Prior to final connection of the TWERC to the surface buoy, final system testing was performed through the riser cable aboard the deployment vessel. With successful operation established, the buoy and riser were connected to the seafloor network and complete end-to-end verification testing was performed over satellite to the Network Operations Command Center (NOCC) on shore. The system is now in operation. The successful installation of the TWERC OCB resulted from strictly adhering to a program management plan, installation storyboard, deployment plan, detailed event table, quality management plan, desktop study (DTS), subsea survey and permits, route position list, load method of procedure, contingency plans and schedule, among other exacting preparation. A step-by-step event table incorporating contingencies for unplanned events during deployment should result in significant cost and schedule savings in addition to the most important aspect, assurance of the safety of personnel and equipment. This was the case in the recent TWERC OCB installation, despite the complexities of coordinating the numerous surface vessels and subsea vehicles required to successfully install the system. This paper also outlines some of the best practices gathered from this and prior cabled seafloor installations, which may assist in future subsea installations. As Benjamin Franklin is purported to have said, “By failing to prepare, you are preparing to fail.”