Bold Endurance: From heavy lifting to deep-sea plowingFeb 28, 2007 12:00 AM
Built for the Russian navy by Hollming Ltd. of Finland in 1978, the 458-by-66-foot ship began life as a heavy-lift vessel. Purchased by Canadian-based Secunda Marine Services Ltd. in the mid-1990s, the ship was taken to a Korean shipyard for an extensive structural refit. The ship then went to England for the installation of cable-laying equipment by charterer Global Marine Systems to make her the 8,300-dwt fiber-optic cable-lay vessel that she is today.
Ship's master, Capt. Doug Corkum, from Nova Scotia, is the descendant of a long line of Atlantic fishermen. He has been with the ship since she was handed over by the Russians. At that time the forward-house design allowed for a 295-by-46-foot-long after hold with a watertight transom door. Secunda purchased two of the three ships in her class, known as a ro-flo ships for their ability to flood ballast tanks to partially submerge so that smaller vessels or floating equipment could be loaded aboard without lifting.
Because she was built as a heavy-lift ship, the whole engine room is under the floor of the cargo hold; and the sidewalls, from the transom forward to the accommodation area, are double walled. The double sidewalls provide ballast. Putting the engine room below the cargo hold provides positive buoyancy, while permitting a large hold open to the stern. This huge area was covered with seven hatch covers that could be lifted off with a mobile gantry crane to create a huge open hold.
The ro-flo design made the ship perfect for conversion to a cable layer. The hatch covers were sealed to form a large open after deck for stowing gear. The watertight stern door was welded shut, and a large generator room was fitted with three Caterpillar 3516B and one Cat 3512 to power the generators that provide 440-volt electrical services for the cable-laying equipment. Ship service at 380 volts is provided by three WÃ¤rtsilÃ¤-powered generators in the engine room.
Forward of that are four huge, round cable tanks that are 42.5 feet in diameter and almost 20 feet deep. Except for a central core that is 10 feet in diameter, these tanks can be filled entirely with fiber-optic cable. The total amount and length of cable onboard will vary with the job to be done, but the tanks can hold up to 5,450 tons of cable. Depending on the diameter of the cable, this is enough to stretch a couple thousand miles.
When cables are laid in deep water, where they are less in need of protection from trawl net doors or anchors, the little strands of fiber-optic cable will be protected by a neoprene armor to a thickness of about 1.5 inches. For shallower waters, the cable will be 3 to 4 inches thick. For a large job, loading the cable can take several days. An additional smaller cable tank can be used as a spare.
The actual cable work is done by a crew with Global Marine Systems. The aft deck, on top of the sealed former hatch covers, is crowded with shipping containers that have been converted for use by Global Marine as offices, labs and special equipment rooms. These rooms are used for splicing cable, controlling the plow that digs a furrow for the cable in the seabed and a number of other technical functions.
Global Marine maintains that it has buried more submarine cable than any other company. The company laid approximately one-third of the 90,000 miles of subsea cable installed in 2001, of which more than 40 percent was plowed into the seabed. Some of that was laid by Bold Endurance.
During the year, Bold Endurance was on contracts in Asian waters doing work like laying cable from Manila to Singapore. "We can spend up to two months at sea,â€� Corkum explained. "We carry more than enough fuel and can make 20 tons of water per day. It is only the food to feed the crew and cable-laying personnel that limits us.â€�
As with research ships, a cable ship has two parallel crews. In this case, Canadian officers, Filipino mariners and Ukranian engine-room workers comprise the crew employed by Secunda. The cable-laying crew, mostly English and Filipino, work for U.K.-based Global Marine. Total numbers vary depending on the particular type of contract, which ranges from inspection of older cables with remotely operated vehicles (ROVs) to the towed-plough laying of new cable. The Barbadian-registered ship has accommodations for 60 people, and a typical ship's crew is 23, leaving lots of room for cable crew.
A recent job for the ship involved the inspection of cables off the California coast. In this operation the ROV was guided along the existing cable as it videotaped the cable and inspected for damage. In other cases the ship may be sent out to locate and repair a break. One technique for locating a break uses an electrical impulse that is sent down the cable and travels along it until stopped by the break. Once the damaged point is located, a simple grapple is dragged across the seabed to snare the cable. Once aboard, the cable is fed into a splicing room on deck where a new section of the appropriate size is spliced in place before the cable is returned to the seabed.
On the job between Manila and Singapore, the crew laid cable out into the South China Sea from Manila to the halfway point. There they marked the location and dropped the cable end to the ocean floor. The ship then went to Singapore and laid cable out from that end. When they arrived back at the halfway point, they recovered the other end of the cable and spliced the two sections together to complete the job.
Depending on the composition of the seabed and the potential dangers posed to the cable by nature or human activities, the crew will bury the cable or leave it exposed on the ocean floor. On the main deck at the stern, a massive 35-ton gantry can be swung aft, taking with it a huge seabed plow. The leading edge is like a farmer's plow, but on the trailing edge there is a slot into which the cable feeds and is laid in the bottom of the furrow. The towing winch is set to render at 40 tons bollard pull. Depending on conditions, the ship can bury cable at depths to 5 feet beneath the ocean floor and at water depths up to 5,000 feet. With the plow, speeds of about a half mile per hour are common, although it can be worked at speeds of almost 2 miles per hour in ideal conditions.
Working in deeper water â€" Corkum reports laying cable in depths to 24,000 feet â€" they simply lay the cable on the ocean floor at speeds up to 6 miles per hour. A complex system of rubber wheels holds the cable back as it is being paid out, so as to maintain an appropriate tension without breaking the delicate line.
Corkum explained that the job of the ship crew is to work with the cable crew to deliver whatever they need. "The cable engineer and the offshore superintendent spend a lot of time on the bridge, where we have a complete set of tension monitors,â€� he said. "Once when we were working in really deep water, the tension started to increase, but the offshore superintendent said to increase speed, and the tension went out. The slight increase in speed reduced the catenary, or belly, in the line, allowing the tension to go down.â€�
It is this close relation between the ship crew and the cable crew that makes this such a successful vessel.
Weather can be a complicating factor. "We have worked in 40- to 50-knot winds, but if it is on the beam, it can cause wear on the cable casing, so we have to stop,â€� Corkum said. "If it looks like it will get real bad, then we cut the cable and do a controlled drop with set ground tackle that can be retrieved later. If it is less severe, we will jog into the wind until it goes down, and then start laying again.â€�
This sort of precision work requires navigation skills and a full slate of position-holding aids. When the ship was converted, a skeg was added at the stern to provide space for two 1,500-hp stern thrusters to match the two 1,500-hp bow thrusters. The main engines are a pair of 3,000-hp Pielstick medium-speed (490-rpm) diesels turning controllable-pitch propellers. The boat has roughly the same power for transverse movement as fore and aft. Equipped with a Kongsberg SDP11 single-station DP-1 dynamic positioning system, it can track to the precise waypoints that the cable layers require, or hold position while the ROV is inspecting a specific section of cable.
Given the complexities of the electronics onboard, Bold Endurance carries Electrical Technical Officer Michael Fearn. He got his sea legs on British Columbia fishing boats and his computer fingers creating video games with the neighbors in a small coastal fishing community. On the bridge, Fearn explained that the DP system approximates the reliability of DP-2 with a redundant operations computer. The DP system is linked to all six of the ship's propellers. As satellites pass over and seas buffet the vessel, the six propellers can end up working quite hard to hold the vessel in position. This circumstance leads to a certain amount of back-and-forth prop action that can put added stress on the equipment and the crews.
When water depths permit and the ship has to hold a stable position for chores, such as tending the ROV, an alternative position reference is available. From a small crane mounted on the port side about midship, a taut wire with a weight affixed is lowered to the ocean floor by a constant-tension winch. At the end of the crane's boom, sensors detect the angle of the wire. The winch maintains a constant tension on the wire, and the sensors note any changes in the angle of the wire. This data is fed to the ship's DP system, which then activates the propellers to restore the angle to its original position, thus keeping the ship stationary in relation to the weight on the ocean floor. This system is typically used in depths of less than 650 feet but can, in calm waters, work to depths of 1,300 feet. It requires much less action by the propellers to hold position.
Another form of reference system is the Kongsberg HiPAP (High Precision Acoustic Positioning) system, used for tracking underwater objects like the ROV. With this piece of equipment, a transducer is extended on a rod about 10 feet out from the bottom of the ship. It then sends acoustic signals back and forth with a transponder mounted on the ROV or the plow, and so charts their location relative to the ship.
When not at sea, Bold Endurance is currently stationed at the cruise-ship dock in Victoria, British Columbia. In her holds is a wide range of cable sizes that equip her to sail on short notice to repair damaged cables anywhere along the Pacific coast of North America. Or they may get a call to go on a longer job laying a new submarine cable from Alaska to the Lower 48. These contracts have a tendency to be assigned when the crew can experience the full force of a North Pacific winter.
In spite of this, the ship attracts a steady crew who tend to return for voyages over the years. The multinational makeup of the crew is recognized in the mess area, where charts of the Black Sea, the Philippines and the United Kingdom share space with those of the Canadian east and west coasts. In this fashion, while the ship is contributing to modern global communications, the charts help to ease the crew's age-old mariner's longing for home waters.Edit Module