Submarine fibre-optic cable boosts Ireland's global connectivity
30 May 2013
The global telecommunications industry is struggling to keep pace with an ever-increasing demand for bandwidth. Despite major advances in optical transmission capability, a lack of new submarine cables between Ireland and the UK threatened to constrict growth of high-tech companies.
During the previous telecommunications boom from 1997 to 2001, a series of submarine cables were installed between Ireland and the UK (Global Crossing 1 and 2, Esat 1 and 2, Solas, Sirius South and Hibernia – Segment C) and between Ireland and the US (Hibernia – Segment A and Hibernia – Segment D). However, after the dot.com bust in 2001, no new systems were built to meet the increasing capacity requirements and to replace older cable systems
This lack of investment over a decade, combined with the establishment in Ireland of companies such as Google, Facebook, Yahoo!, Microsoft, PayPal and their associated data-storage facilities, resulted in a capacity-deficit of submarine cables between Ireland and the UK.
In 2009, Sea Fibre Networks sought to address the infrastructure deficit, with plans to install a high-fibre count network, the CeltixConnect cable, between Ireland and the UK. The cable comprised 72 fibre pairs, thereby doubling the effective capacity between the two countries.
A detailed feasibility study was undertaken to establish an optimum sub-sea route that addressed the following key points:
1. Integration with terrestrial cable systems and major communication nodes
2. Availability of suitable landfalls;
3. Shortest possible sub-sea route;
4. Diversity from other cable systems;
5. Ability to achieve burial/protection of the cable throughout the route;
6. Avoidance of established fishing grounds;
7. Minimisation of cable and pipeline crossings;
8. Ability to satisfy stringent permitting requirements.
On the Irish side, East Point Business Park was a key focal point, as it is a hub for a large number of terrestrial networks operated by various telcos in the Dublin area. Three potential landfalls were identified and assessed but, taking all of the factors into account, the outcome of the feasibility study indicated a preferred landfall at Dollymount with backhaul to a Shore Station at East Point.
On the UK side, the presence of a new, European-funded open-access fibre optic cable across the north of Wales influenced the selection of a landfall at Anglesey. Five potential landfalls were identified and, following a detailed assessment, the preferred location was at Porth Dafarch on the west coast of Anglesey.
Of all the factors to be considered in sub-sea routing, the ability to bury the cable in the sea bed was the primary concern. Typically, cables are buried by direct placement in the sea bed using a sub-sea cable plough. Target burial depths of 500mm to 1,000mm are preferred. A burial depth of 300mm is the normal minimum, so as to avoid the risk of subsequent cable damage from fishing gear. Avoidance of mobile bedforms is also critical to avoid the development of free-spans in the future.
A stable, sandy or muddy sea-bed is ideal for cable routing, but this is not always achievable. The Irish Sea, being constricted by Northern Ireland and Scotland, Dublin and Anglesey, and Wexford and Pembroke has wide-ranging sea-bed conditions and poses significant sub-sea challenges in the form of areas of mobile sand-wave fields, mega-ripples, compacted soils and areas stripped of sediment or with only a veneer of cover.
When adequate burial cannot be achieved, it may be necessary to incorporate protective measures that include customising the armour profile of the cable (ranging from single armour to double armour, triple armour or rock armour). Cast-iron shells are typically used at shore-ends and polyethylene casings are employed at cable/pipeline crossings
The feasibility study, which was carried out to select a route for the submarine cable, was based on published data, material from the company’s previous submarine pipeline and cable studies, industry information on the operational history of existing submarine cables and experience of submarine pipeline and cable installation in the Irish Sea. This exercise resulted in the selection of a route corridor extending from Dublin to Anglesey.
In order to determine the final sub-sea route, the burial assessment, the armour profile and the expected plough tensions and lay speed, a detailed marine survey was carried out. The geophysical survey comprised bathymetry, side scan sonar, sub-bottom profiler and magnetometer.
This was supplemented with a geotechnical survey comprising grab samples, vibrocores and core penetrometer tests. The geophysical survey covered a 500m-wide survey swathe in the offshore area and this was complemented by shallow draft cable innovator and diver survey in the inshore areas and at the landfalls.
Having carefully selected an optimum route corridor, the evaluation and assessment of the marine survey resulted in the selection of a definitive line for the sub-sea cable route. This was defined in latitude/longitude co-ordinates to WGS 84 for general purposes and in UTM 6 co-ordinates to WGS 84 for precise positioning for cable installation purposes. The route design is shown in Fig 1.
The line that was selected exits Dublin Bay and swings north-eastwards past the Howth Peninsula to a point approximately 9km east of Lambay. This routing was selected to achieve good burial and to get north of an extensive area of sand-wave fields and mega-ripples.
At Turning Point 05, the route follows a curving line eastwards to Turning Point 13. This line lies to the south of intensive fishing grounds, whilst staying north of the extensive area of sand-wave fields and mega-ripples.
At Turning Point 13, the route swings south-east across difficult sea-bed conditions. The sea bed is firm over this section and achieving adequate cover required intensive burial assessment engineering. The route keeps to the south of the Holyhead Deep and 10km off Anglesey, at Turning Point 29, it swings north-eastwards for the approach to the landfall at Porth Dafarch.
Whereas the straight-line distance from landfall to landfall is 101km, the length of the actual route is 131km.
LICENCES, PERMITS & AUTHORISATIONS
There is an onerous and often complicated permitting process covering both Irish and UK jurisdictions. Key permits include a Foreshore Licence for Marine Survey and a Foreshore Licence for cable lay on the Irish side, and a Crown Estate Licence and Marine Consent Unit approval on the UK side – the former two being by far the more difficult. There were also numerous additional permits relating to the landfalls, including private wayleaves and environmental permits.
In the case of CeltixConnect, a landfall as close to Dublin City centre was required, greatly adding to the complexity and timescales for obtaining all of the requisite permits, licences and authorisations. This element of the permitting, together with the Foreshore Licence for main-lay, dictated the critical path for the project rather than engineering or procurement.
Cable-lay vessels have always been in short supply and were particularly so for this project, due to alternative wind-farm work. In this regard, a lay cable innovator needed to be procured by tender and booked for a specific time-slot months before the proposed lay date and in advance of the completion of final design.
Cable manufacturing also takes up to 20 weeks, necessitating very early-stage finalisation of cable armour profile. This resulted in no margin for delay in the permitting process and the prospect of a winter lay for the cable system, which introduced significant additional weather risks.
The contract for installation of the cable was awarded to Global Marine Systems Ltd. The main-lay vessel was the Cable Innovator (Fig. 2), a 145m long specialised ship. A shallow draft vessel, MV Union Beaver, was used to lay the shallow shore-end at Dublin.
The installation sequence developed and agreed with Global Marine Systems involved:
1). A pre-laid shore end at Dublin involving the landfall at Dollymount (see main image, above) extending parallel to the North Bull from the Beach Manhole to the low water line. The route then swung on to an easterly line to a pre-determined point off the Bailey at Howth in 20m of water. The cable was buoyed at that point.
2). The Cable Innovator completed a pre-lay grapnel run from Dublin to Anglesey to clear the route of obstructions such as ropes, nets, cables, anchors and general debris. It then completed plough trials over the length of the route from Anglesey back to Dublin.
3). The Cable Innovator, a deep-draught offshore vessel, recovered the pre-laid section of cable off the Bailey at Howth and completed and tested the splice joint. The vessel then commenced main-lay from Dublin to Anglesey at a general rate of 1km/hr.
4). On arrival off Anglesey, the Cable Innovator anchored at the 10m water depth in direct line with the narrow inlet off the landfall at Porth Dafarch. A pull-rope was brought ashore and this was used to pull the buoyed cable from the vessel to the Beach Manhole. (Fig. 3)
The cable was effectively installed within 30 days and post-lay burial at pipeline and cable crossings and in areas of stiff clays was completed approximately 10 days later. These periods included weather down-time, and having regard for the fact that the installation was done from mid-December 2011 to mid-January 2012, the pre-planning proved to be effective and the performance was satisfactory.
To date, the CeltixConnect cable has performed exceptionally well with no incidents. This is particularly important, as there is general industry acceptance of a cable if no issues arise in its first 12 months of service. A detailed programme of cable awareness is continuously carried out by Sea Fibre Networks, including liaison with fishermen, harbour authorities, the Irish Coast Guard and other interested parties. An automatic information system is in place and is also monitored to determine shipping and fishing patterns with early warning procedures in place to enhance the protection of the cable.
The CeltixConnect cable has been a very successful project. It greatly enhances Ireland’s global connectivity and underpins Ireland’s position as an ideal location for multinational companies and the associated development of large data centres.
Sea Fibre Networks is now at detailed design stage on the FastnetConnect project, a high-fibre cable between Cork, Cornwall, Guernsey and France. Ultimately, this will provide a diverse resilient system between Ireland, the UK and Europe, linking up with most of the current transatlantic and Europe, India and African gateway cables.