On Nov. 18, 2006, the semisubmersible, heavy-transport vesselMighty Servant 3 sailed from Trinidad to Luanda, West Africa, with the Transocean-owned semisubmersible drilling rig AleutianKey on board. During the discharge of the rig, at 07:53 local time, the Mighty Servant 3 went down in 50 m (164 ft) of water. Fortunately, no personal injuries were suffered and the rig was safely discharged.
"When the incident occurred, we immediately started to tender the salvage to raise the vessel," says Eugène van Dodeweerd, Dockwise department manager, Fleet Supervision. "At the same time we started to prepare and write repair specifications based on the vessel’s existent electrical and machinery design."
In order to determine whether it was feasible to repair and reinstate the vessel, it was vital that structural damage was limited. Furthermore, critical machinery such as the main engines, reduction gear boxes, and steering gear were all saved for re-use. Dockwise set up a plan to safeguard these critical components at Luanda upon resurfacing of the vessel.
To preserve the main engines, the seawater had to be pumped out and freshwater pumped in to clear away all salty residues. The engines were then flushed with fresh lubricating oil and special preservative fluid before removal.
On May 26, 2007, nearly six months after the incident, SMIT Salvage lifted the vessel from the seabed and delivered it back to Dockwise. Since the structural damage and further inspections could only be assessed properly in drydock, the vessel was towed to the nearest docking facility at Cape Town, South Africa, where it arrived three weeks later. Preserved critical machinery components were removed for immediate dismantling and cleaning.
"While at Cape Town it was determined that structural damages to the vessel were limited in extent and repairs would be feasible," explains van Dodeweerd. "Thereafter, service teams could start cleaning and stripping all electrical cable, accommodations, upholstery, and so on. Furthermore, all interested yards and electrical subcontractors were invited to inspect the vessel and prepare their bids."
After a swift tendering process, the repair contract was awarded to Grand Bahama Shipyard and the tow toward the Bahamas was undertaken in November 2007. The vessel arrived at its destination in Freeport on Jan. 23, 2008.
Reconditioning program
"This is a reinstatement project in a magnitude that has never been performed before – no one has ever taken a vessel submerged in 50 m of seawater for five months and brought it back to service," says van Dodeweerd. The vessel has been entirely rebuilt starting with the steel hull. Machinery, electrical systems, and equipment have been newly fitted to the latest standards and designs, using the original functionality and foot print.
The restoration program at Grand Bahama Shipyard included a fitted accommodation block and buoyancy casings heightened by 4 m (13 ft) each.
The accommodation block was extended by inserting an additional layer and furnished with entirely new upholstery. The capacity has been increased to accommodate 50 persons, to improve service to clients, and to provide additional room for extra crew members and Dockwise personnel.
The two Wärtsilä (W12V38A) engines were removed from the vessel locally, fully dismantled, and later shipped in parts to Wärtsilä Netherland’s workshop in Zwolle. "Such work has never been done before by Wärtsilä," says Martin van der Voort, regional manager, Wärtsilä Netherlands.
"The vessel had been resting on the seabed for six months," he adds, "but we have succeeded in retuning these engines to optimum operational efficiency. All main components have been re-used and the engines were re-built." Connecting rods and all other engine parts were severely corroded and were replaced with new components from Wärtsilä service stocks.
Dockwise also strengthened technical safeguards and procedures, including the complete renewal of ballast control and level systems, with an increased level of control, monitoring, and safety redundancy. Additionally, various ballast valves have been doubled and casings increased in height by 4 m (13 ft) to create additional buoyancy and redundancy during submerge operations.
Dockwise also modified and strengthened procedures around the ballasting operations which included avoidance of concurrent ballasting operations of cargo and vessel; assurance of a ballasting plan and proper execution; implementation of further safety and check stops; and increased ballast management, with adequate check loops by all vessel staff.
TheMighty Servant 3 rejoined Dockwise’s fleet last month and is scheduled to embark on its first project soon.
