Computer-generated image showing the vessel with its newly installed J-lay tower.
Heerema has joined the ranks of contractors converting giant crane vessels for deepwater activity. Heerema said that, unlike its rivals, most of whose actions were speculative, the Dutch firm had the guarantee of a five-year construction contract for BP's deepwater Gulf of Mexico fields.
Following the award last November, the semisubmersible Balder entered the drydock at Verolme Botlek yard in Rozenburg, and work began in January. The conversion program will cost around $160 million, and represents the biggest project of its type undertaken by the yard - more extensive than the J-lay conversion of the S7000 that it managed in 1989-99.
By the scheduled completion date in January 2002, more than 1 million man-hours will have been devoted to the project, with 600 personnel onboard during peak periods. Also, the program is providing work for numerous marine engineering contractors in The Netherlands. Among these is IHC Gusto Engineering, which handled the feasibility/design studies for the vessel conversion, including deck strengthening.
According to Verolme Botlek, the program comprises three large sub-projects, all being undertaken simultaneously:
- Installation of a complete dynamic positioning package. This DP system incorporates seven thrusters, supplied by Drunen-based John Crane Lips, each with an output of 3.5 MW. These have been installed under the vessel's pontoons.
- Power for the thrusters comes from six newly added engine rooms, each housing a 4.32 MW MaK diesel engine, located next to the thruster area.
- A Kongsberg DP and vessel management system is also being installed, which alone will require 200 km of electric cabling and 20 km of piping.
Since the Balder is over 20 years old, numerous other systems are in need of replacement or repair. This work is covered in the lifetime enhancement package - the second major sub-project. Facilities will be added on the deck to receive the 2,300 metric ton, 120 meter high J-lay tower and associated components. This is being provided by Huisman-Itrec, which also supplied the J-lay system for the S7000 conversion.
A recent photo of the Balder in drydock at the Verolme Botlek yard near Rotterdam.
The Balder's pipelay tower will be mounted on a box structure added to the vessel's port side, and will consist of two box girders connected by crossbeams and braces. A 25-meter-long lattice piece can also be inserted between the top crossbeam and the tower to change the configuration from quad to hex mode.
The traveling block runs between the box girders and is powered by a dual-drum, main hoist winch mounted on the rear of the tower, while the welding and coating stations are situated at the lower end. The welding station also contains the hang-off clamp. Directly above it is the external line-up tool. Below the tower will be a lattice stinger with roller boxes to guide pipe joints to the seabed.
The joints will be fed through via a lattice structure loader, which runs on two sets of rails - one on the vessel deck and one on the tower itself. The loader will be pulled up against the tower using a loader hoist winch, also mounted on the rear of the tower. This loader is fitted with clamps that will be used to pick pipes up from the deck handling systems, then transfer them to the tower. Another set of clamps within the tower will be employed for the hand-over.
The system will be able to lay pipes in diameters from 6.625 in. to 32 in., with coating diameters up to 50-in., and at laying angles of 90 degrees to 50 degrees. In quad mode, the tower will be handling 48-meter joints with a maximum weight of 72 metric tons, and a pipe tension of 1,050 metric tons. In hex mode, the joints handled will be 72-meters long, also with a maximum weight of 72 metric tons, and a pipe tension of 52 metric tons. The tensioning systems are being designed and manufactured by SAS in Gouda.
The tower will be able to handle in-line items with outside dimensions larger than can pass through the hang-off clamp/roller box system. This will be achieved through a sidestep operation, in which the pipe joint containing the in-line item will be brought into the tower, lined up, and welded to the pipe. The welding/coating station and roller boxes will then be opened on the forward side.
Subsequently, the hang-off clamp holding the pipe will be skidded out of the tower, with the free upper end of the pipe guided by a clamp. Using the vessel's cranes, the pipe will be lifted out of the hang-off clamp, which will also open on the forward side. The pipe will then be lifted clear of the tower, lowered and re-positioned in the hang-off clamp. Finally, the pipe is brought back into the tower and normal operations resume.
Verolme Botlek has appointed separate project managers to supervise strengthening of the deckbox and the columns/pontoons. They are supported by project managers responsible, for example, for the engine rooms and thruster rooms. An electrical project manager has also been appointed to direct subcontractors.
In November, the Balder should be moved out of drydock for the thruster mounting operation, followed by further commissioning and sea trials. If all goes to plan, it will sail out of the yard on January 11. The vessel's existing cranes have not been removed, as the BP program includes heavy lifts for the Crazy Horse, Mad Dog and Holstein developments. In J-lay mode, it will be responsible for part of the Mardi Gras export system, in water depths dipping beyond 2,000 meters.