Installation Details

The vessel to be used, the Ile de Sein, is a 10,000 DWT purpose-built cable ship fully equipped with all the necessary equipment, tools and facilities to safely handle and install, joint, test, and power the submerged plant including simultaneous lay and plough burial. She can hold over 6,000km of cable in her tanks, and is designed for the installation of trans-oceanic cables in all weathers. As well as the main engines, she has 5 thrusters that allow her to hold position in most weathers while working. Position keeping (dynamic positioning, or DP) is via redundant computer systems, controlled by GPS. She has 100 tonnes bollard pull for pulling the cable plough, and she will be equipped with a 150-200 HP cable burial ROV if external resources are not used.

The NEPTUNE Canada cable system will be loaded into the circular cable tanks on the cable ship. It is packed in horizontal layers by loading crews that hand place the cable, making sure it is laid tightly within the tank and protected from damage when the ship rolls during storms. Two loading crews are used so they can work in shifts – usually 20 minutes on, 20 minutes off; loading will take up to a week.

The repeaters (which optically amplify the light signals in the fibre) are spliced into the cable before loading onto the ship, but are not put into the tanks. Instead, when the loading crew comes to a repeater, the cable is led out of the tank to a rack where the repeaters are stacked in a controlled environment. The cable loading proceeds by leading the cable back into the hold and continuing the circular placement.

On this system, Alcatel-Lucent has decided to splice in the branching units during installation. The branching units, with cable tails, will be stored alongside the repeaters on the ship for easy access and splicing into the cable as required.

A pre-grapnel run (PLGR) along the proposed cable route will shortly precede the main installation operation. The objective of the PLGR is to use towed grapnels to clear any sea bed debris, for example wires or hawsers, discarded fishing equipment etc. which may have been deposited along the route. PLGR operations will normally be carried out by a vessel of opportunity specifically fitted out with winches and grapnels and capable of sustaining slow speed and good positional control.

Cable installation will start in Port Alberni where the cable ship will stand off in about 30m of water. It will hold its position using dynamic positioning. A rope will be pulled to shore by a small boat and attached to pulling equipment. The cable end will be brought on deck and buoys will be attached as it is pulled (while floating) towards the beach manhole. Once the cable end is ashore, and the cable is hanging under a line of buoys, divers will bring the cable end into the beach manhole, where it will be fastened to the manhole and prepared for jointing to the land cable that has already been installed. The divers then cut the buoys loose, and check that the cable is secure on the seabed before the ship starts laying away down the Alberni Inlet. This method of installation allows for a great deal of control of the placement of the cables.

Once the last buoy is released from the cable, the ship will commence installation down the Alberni Inlet. This portion of the installation is surface laid, and is managed to a high degree of accuracy by the use of dynamic positioning and controlling the rate that the cable is payed off the ship.

Once out of the Canal, the cable will be buried about 1m into the seabed, across the shelf and upper continental slope down to 1500m water depth, wherever the seabed is suitable for burial. Burial is achieved as the cable is laid, using a 30 tonne SMD3 plough. This plough has a single vertical share made of two pieces of steel plate. The share cuts into the seabed, and the cable, which runs between the two plates, drops to the bottom of the cut. As the plough leaving the cable securely buried.

Installation of branching units is complex, requiring the vessel to lower the branching unit to the seabed while holding the two cables on deck. The cables are then placed on the seabed in such a way that they are not crossed or twisted. Luckily the telecoms industry has developed techniques for installing branching units, so this complex operation is expected to go smoothly.

After the loop is laid, the ship will go back over some of the burial areas with its Remotely Operated Vehicle, inspecting the results of the ploughing and burying the plough recovery areas and branching units where possible.

Once the installation is complete an as laid position list will be generated by Alcatel-Lucent and this position list will distributed to the fishing community, Transport Canada, Canadian Hydrographic Survey, Fisheries and Oceans Canada and other interested parties. All as laid details will also be made available through the NEPTUNE Canada web site.