What kind of dynamic positioning do we need when submarine cable laying?
Seatrek Marine Solutions Limited
Submarine cable work is recognised worldwide as complex, and difficult project. How do you make it easy for your equipment to handle it? The answer is in GE SEASTREAM™.
The ideal situation for submarine cable laying
1. The depth of the water is changing, the direction of the vessel is changing, can your vessel and submarine cable laying equipment really follow the desired target route with efficiency, consistency, and precision?
2. Is your vessel capable of proactively avoiding damage to cables and cable-laying equipment when faced with the invisible depths of the sea?
The ability to maintain a high degree of co-frequency between the subsea machinery and the working vessel without deviating from the target trajectory, thus increasing the efficiency of cable laying, and saving project labour costs, is one of the requirements of the clients. The type of dynamic positioning systems used will largely determine whether this expectation can be achieved.
What kind of Dynamic Positioning Systems (DP) are required for a cable-laying vessel?
Even though the general term 'cable-laying vessel' is used to describe the vessels used for submarine cable installation, it is important to understand that submarine cable installation involves two different phases of operation: 'cable laying' and 'cable maintenance', each of which has a different focus on the requirements of the DP systems.
Cable Laying Vessels
The DP systems need to be able to precisely control the vessel's movements to help the vessel and the cable-laying equipment to complete the "forward - trench - lay cable - fill" cycle according to a predetermined route and frequency, thus increasing the efficiency of cable-laying operations. But just as important as this process is the need for the DP systems to be not only precise, but also to know how to avoid damage to the cables and to prevent damage to the submarine cable-laying equipment.
In addition to meeting the demands of regular cable-laying operations, the DP systems on cable maintenance vessels need to support more elaborate task sequences, such as specifying the location of cables, retrieving them, repairing them, and re-laying them. The DP technology used on such vessels therefore often requires more detailed and standardised positioning functions and must be able to support the work of ROV (underwater robots).
Enabling efficient synergy between vessel and cable plough
The latest generation of SeaStream™ systems support and covers all the needs of a professional cable-laying vessel, including cable-laying operations and cable maintenance. With decades of research and development experience, GE has worked with submarine cable work vessel owners and system operators to optimise DP functionality specifically for cable laying operations, resulting in more efficient and satisfying submarine operations.
Automatic cable laying mode
Focusing on the needs of cable-laying operations
Precise control of the vessel's trajectory and speed according to a predetermined route
The most typical applications for the SeaStream™ DP systems in auto-tracking mode are cable laying, pipelaying and surveying. In automatic track control mode, the vessel follows a pre-set track at a relatively low speed; at the same time, all thrusters are used to precisely maintain the vessel's position, bow, and speed. The operator can intervene at any time: changes can be made to the bow and speed settings and the route can be transferred to the SeaStream™ either by manual input or by automatically downloading the pre-set track from an external survey/cable laying computer.
Automatic calculation of the vessel's path to match the cable plough’s route
When laying cable in deep water, the vessel's track may not always match the cable path exactly. When the cable route is imported, the SeaStream™ DP system automatically calculates the necessary vessel tracks, considering changes in direction and depth, to ensure that the actual cable plough route is precisely matched to the pre-determined route.
High tension reduction function protects your equipment and cables from damage
When a laying vessel is towing a cable plough (or other similar equipment), the SeaStream™ DP systems will automatically measure the tension on the towing cable of the cable plough: if the measured tension exceeds a pre-set alarm value, the system will automatically activate the high-tension deceleration tension control function and gradually reduce the speed to protect the towing equipment and cable.
If the buried plough is caught in a subsea obstruction, the SeaStream™ DP systems will control the vessel's speed so that it is eventually reduced to zero, bringing the vessel to a standstill. Once the operator has taken the necessary safety measures, the vessel will resume cable laying operations.
Tips: In the early 1980s, a cable working vessel called ITM Venturer was laying DC cables for one of the world's busiest shipping routes, the English Channel. GE's first attempt to apply the Automatic Cable Laying Mode of its DP systems to this type of vessel provided an extremely important reference for the installation of similar projects since then.
The most cost-effective system configuration at GE SEASTREAM™
If you want to know what configuration stands out in cable-laying performance, GE will tell you. In the configuration of the GE SEASTREAM™ DP systems, the strengths of the various measurement systems in use will be combined to consider the best use of each technology for cable operations, for example, hydroacoustic positioning for marking the coordinates of subsea cables, and tensioned rope positioning for vessels that need to be positioned for long periods of time to carry out cable repairs.
GE's partnership with Sonardyne enables a strong lock on cable-laying tracks
In China, GE has partnered with Sonardyne, a leading brand in the field of acoustic positioning, to support the excellent performance of cable-laying path positioning: the high accuracy of the Sonardyne USBL ultra-short baseline position measurement system, which is unaffected by water depth, and the ultra-high speed of data transmission, provide a strong scientific basis for the design and implementation of cable-laying paths and cable protection measures.
Sonardyne USBL Position measuring systems
The GE SeaStream™ DP systems in the following submarine cable laying vessel applications were supplied by Seatrek and are equipped with the Sonardyne Ranger 2 USBL system solution.
Case Study ：“Nan Dian Jian Cha 01” 49m Cable Maintenance Vessel
The first dynamic positioning vessel capable of carrying out both high-speed cruising and low-speed inspection tasks for 500KV submarine cables in China.
Main application： Submarine cable laying and maintenance operations
Sonardyne Ranger 2 USBL
DP Level: CCS DP-1
1) The project has successfully filled the gap in China's domestic submarine cable operation and maintenance inspection technology
2) The Sonardyne Ranger 2 USBL system, combined with the power industry's first robotic system equipped with acoustic, optical and electromagnetic inspection equipment for submarine cable inspection, enables the precise location of submarine cable routes and provides a scientific basis for taking targeted submarine cable protection measures.
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GE SeaStream™ Dynamic Positioning Systems