Workboats: The World's Largest OSV

There are several large offshore service vessels working in the Gulf of Mexico, but none so big and powerful as the Laney Chouest. At 348 ft. long by 72 ft. wide with a 31-ft. deep hull, the Laney Chouest simply dwarfs anything in the Gulf. Built by Edison Chouest Offshore, Galliano, La. at their North American Shipbuilding facility, the vessel is already at work in the Gulf on a charter for Shell Offshore.

"This vessel was designed and built for a very specific mission-to preset mooring systems in 10,000 ft. of water safely and efficiently," said Roger White, senior vice president of Edison Chouest Offshore. "The real market for this vessel will be in the 5,000-10,000 ft. range and the vessel is certainly big enough to hold all of the wires, suction piles and necessary fittings, "White added.

Shell Offshore agrees with that assessment. " Overall the vessel is a more cost effective way in the process of drilling and setting subsea equipment," said Mary Dokianos, Shell spokesperson.

For example, the vessel can hold six mooring piles, not two or three as on smaller, less powerful boats. "That makes installation quicker," Dokianos added. In a towing mode, the Laney Chouest can move rigs faster. "Less towing time means less downtime for a rig with a high day rate, again saving us money," Dokianos stated. It is also obvious that Shell has lots of construction projects in mind for the Laney Chouest. "It will no doubt be used for lots of subsea component installation, remarked Dokianos. When the full capabilities of the Laney Chouest are known, Shell will find more and more tasks for this super sized AHTS.

Laney Chouest defines the meaning of an Anchor Handling Tug Supply (AHTS) vessel by also featuring huge below tanks for resupply of rigs and it also is a ROV support vessel and is capable of many types of subsea completion work with its four cranes. The multi-mission capability of the Laney Chouest is one of its greatest advantages.

Towing rigs and presetting suction piles and other anchoring devices call for plenty of winch power. In the case of this vessel, the winch needed did not exist so Aker Brattvaag, Sovik, Norway built the world's most powerful towing winch for the Laney Chouest. The unit is a four-drum model where each drum can hold 10,990 ft. of five-in. wire with a towing capacity of 600 metric tons in low gear.

Four secondary winches each hold almost 14,000 ft. of five-in. synthetic rope. Two tugger reels with a 15-ton pull and five tugger reels with 12-ton pull each are part of the towing package. Towing gear includes a pair of Triplex V-300 vertical Pop-Up tow pins, two Triplex H700 Shark Jaws, a flush towing Padeye and two 14-ft. diameter stern rollers.

Towing gear also includes a 350 metric ton Hydralift fitted with two 10-ft. diameter sheaves and a two metric ton knuckle crane with a 10-ft. radius.

Laney Chouest can also visually check the status of pile locations, pile placements and other sub sea work with an Oceaneering ROV unit mounted on an A-frame on the port side of the vessel. A 42-in. Moon Pool is located aft for keel hauling objects. The A-frame tilts forward so the winch line is directly over the Moon Pool

Power to Spare

All AHTS vessels feature horsepower ratings in the five figures. But to power the world's largest anchor handler took a specially designed power plant. Four Caterpillar-MAK 6M43 diesels each develop 7,250 hp for a total main power of 29,000 hp. The Caterpillar 6M43 is an inline six-cylinder diesel with a single pipe turbocharger, two circuit cooling and designed for heavy fuel operation. The engines were made in Germany by Caterpillar's MAK division. The local Caterpillar dealer Louisiana Machinery Power Systems, Reserve, La. handled the installation and startup details.

This engine was introduced to the market in 1998. In-line versions in 6,7, 8 and 9 cylinders are available. More than 180 engines of this type have been sold worldwide with over 50 being the in-line six configuration.

The engines are setup in a unique arrangement. Engines one and two both drive a Flenders reduction gear. From the center of that gear is coupled a propeller shaft that drives a 4,700 mm diameter changeable pitch propeller in a kort nozzle. The gear is also designed so that it takes outputs from each engine, so that each engine drives a 3.5 MW shaft generator.

The other two engines are setup in an identical manner with those two engines also driving a propeller and two 3.5 MW shaft generators. The electrical power generated by the shaft generators is used primarily to operate the anchor handling winches, other towing gear, onboard cranes and the thrusters.

A trio of Caterpillar-powered gensets supplies ship's power. Caterpillar 3512 engines generate 1,330 kW of electricity each. A Caterpillar 3406 generator powers a 300 kW emergency generator.

Laney Chouest has five thrusters for excellent vessel maneuverability and dynamic positioning station keeping. In the bow are two 1,500 hp tunnel thrusters and one 2,700 HP drop down azimuth thruster. In the stern is one 1,500 hp tunnel unit and a 2,700 hp Azimuth thruster. All thrusters are by Ulstein.

Super Supply Boat

As a supply boat, the Laney Chouest posts some pretty impressive numbers.

Capacities are:

Liquid Mud 7,367 Barrels

Fuel Oil 377,791 gallons

Ballast/Rig Water 663,169 gallons

Potable Water 42,332 gallons

Dry Bulk 12,583 cu. ft.

The dry bulk is contained in three almost equal sized tanks and can be delivered at 80 psi. The aft cargo deck has an open, clear area of 10,276 square feet and measures 183.5 ft. by 56 ft.. Cargo carrying capacity is 3,000 long tons.

Deadweight tonnage of the vessel is 5,224 long tons at load line draft and 2,975 long tons at normal operating draft. Speed at normal operating draft is surprisingly fast for a vessel of this size and weight: 17 knots. Bollard pull at load line draft of 24.75 ft. is 360 metric tons.

In addition the vessel carries three cranes on deck to assist the vessel in lifting cargo and mooring systems on deck, offloading material to shore, to other vessels or to drilling/production rigs.

Cranes include two 20-ton capacity fixed boom units with a 45-ft. radius and a 2.5-ton knuckle boom unit. Cranes are Alaska Marine from Green Marine, New Orleans.

Accommodations on the Laney Chouest include two four- person rooms, 19 two-person rooms and 12 single rooms for a complement of 58 people. Each cabin has a separate head and spaces also include a ship's office and a two-bed hospital.

The Laney Chouest is setup for DP-2 operation as would be expected for such a sophisticated vessel. Three bow thrusters and a pair of stern thrusters is the heart of the station keeping system. Four shaft generators insure redundant power supplies as required by ABS for DP-2 operation. Independently operating rudders, controllable pitch propellers are other important elements of the DP-2 system as well as redundant input systems such as multiple wind birds and duplicate GPS units. Stability of the vessel is enhanced by bilge keels, a bulbous bow and two passive anti-roll tanks.

A Super Superstructure

The superstructure is essentially six decks high topped by an area that hold air conditioning condensing units to heat and cool the superstructure and the stacks for the engine exhausts.

The main deck of the superstructure contains a large galley and mess area plus food storage in coolers, freezers ands pantry areas. A large TV lounge is adjacent to the mess area as is a reading lounge. Further aft in the main deck superstructure is a change room with lockers and laundry facilities. On the 01 level are several two-person cabins and additional laundry facilities. A workshop, paint locker, CO2 bottles in their own separate locker space plus the two-bed hospital. On the 02 level are several two-person cabins plus dayrooms for the engineer and assistant engineer. Forward of the superstructure at the bow is the anchor windlass/mooring winch with two 52 mm chain cable lifters with 18 metric ton capacity. The 03 level contains additional quarters plus dayrooms for the captain and the mate. Level 04 has an electronics room forward plus mechanical rooms for the HVAC and the emergency generator. The ship's office, a battery room and a locker are also on this level.

The pilothouse is located on level 05 and is the nerve center of the vessel with the forward and aft helm control, chart tables, counters, a head and a computer desk behind a half-height wall. Another area of the pilothouse has receptacles for laptop computers while the GMDSS communications system is centralized in an area near the computer desk. Joy sticks at opposite ends of the pilothouse aft controls the dynamic positioning system. They also act as wing stations for the vessel, although they are located within the pilothouse superstructure.

Additional cabins are located on the lower deck forward just aft of the forepeak ballast.

In a Class by Itself

Laney Chouest is classed as ABS Star A-1 Unrestricted Ocean Service, ABS Star AMS, ABS Star Towing Service, ABS Star DP-2, USCG Subchapter L (OSV) and I (Industrial), USCG Minimally Manned Engine Room, SOLAS '99 and Marpol '99.

The delivery of this super AHTS begs the question, "Will Edison Chouest build other even larger vessels for deep water service?" According to Roger White, "We'd like to believe this is not a one-off project. The key is not necessarily size, but efficiency and safety, and this vessel delivers everything we had hoped for."