The Seabex One, a combination offshore rig support vessel and a dynamically positioned diving mothership, was built by Nobiskrug Werft G.m.b.H., of Rendsburg, Germany, for Seabex Industrielle Tiefseetechnik G.m.b.H. of Germany and Comex of France.
Seabex One was designed to provide a range of services including support of divers, underwater welding, and the installation and maintenance of offshore drilling rigs and fixed structures. The vessel also is equipped for fire-fighting and is capable of evacuating up to 500 people from stricken offshore structures.
A large moonpool is incorporated in the vessel, measuring 15 meters by 8 meters (about 49 by 26 feet) which Seabex claims is the first of a size and configuration that ensures there is sufficient access for lowering the underwater vehicles and equipment. The vessel's deepsea saturation diving system allows up to 16 men to work at three different levels to a maximum depth of 450 meters (1,476 feet). The diving equipment can be lowered either through the moonpool or over the side.
The Seabex One is equipped with seven decompression chambers and a hyperbaric rescue vessel for 12 divers. Other underwater-related equipment includes a welding habitat for constructing oil and gas pipelines, pipe alignment frames, and a cable burying machine. Lockout submersibles are available as are one-atmosphere diving systems.
The moonpool is surrounded by a covered deck space, and the remainder of the deck provides about 1,000 m2 of open space having a load capacity of five tons/m2 — specific areas of which are strengthened to permit the installation of winches, davits, and other gear.
Equipment handling is facilitated by a two-ton mobile crane and a Liebherr offshore crane having a 50-ton capacity at a radius of 15 m, or 100 tons when operating through the moonpool. The crane is fitted with a heave compensation arrangement which can maintain its boom steady in relation to either the sea floor or to another vessel alongside. It can operate to a depth of 300 meters. The vessel also is fitted with a 100-ton capacity H frame at the stern.
The Kongsberg fire-fighting system consists of four monitors of 1,800 m3/h throughput, powered by two gas turbine driven pumps delivering 3,600 m3/h each at a pressure of 15 bar. The fire monitors are inertia stabilized and can provide accurate cover even in bad weather, which Seabex officials regard as an improvement over other systems.
The vessel's maneuverability and propulsion are supplied by a combination of Pleuger ducted propellers and transverse thruster units. Two reversible fixed-pitch nozzle propellers fitted at the stern, which can be steered through a full 360 degrees, are capable of delivering 2,300 hp each at 202 rpm. They are powered by two AEG electric motors running at 700 rpm.
Two similar units are mounted at the bow, each with an output of 1,500 hp at 238 rpm. These are aided by two lateral thrust Pleuger fixed blade units — one forward and one aft — of 800 hp each.
The complete arrangement is controlled by a Kongsberg Albatross 503 dynamic positioning system, which uses data obtained principally from an inertial platform, an acoustic reference system, and two taut wires. The Seabex One wires are attached to an above-water part of the structure near which it is station keeping, as contrasted to other taut-wire systems that are linked to weights on the sea floor. The multiple data sources ensure a safety margin in the event any part of the system breaks down.
Power for the electrical propulsion is supplied by five auxiliaries, each consisting of an MAK 8M332AK engine and an ADG generator, producing a total output of 6,450 kw, using fuel of 30 cSt (200 sec. Redwood), and an emergency generator set of 300 kw.
Two engine rooms are needed to house the equipment and a large control room is situated on the lower 'tweendeck above the control room. There are accommodations for 86 persons, two evacuation rooms with 50 bunks each, and a hospital onboard. The Seabex One was built to Det norske Veritas classification.