Semi-submersible with redundant DP and azimuthing pods

China?s Guangzhou Shipyard International has finally completed Tai An Kou, the first of two 18,000 dwt semi-submersible heavy lift ships it was contracted to build by Chinese company Cosco Guangzhou. It is the first vessel of this type to feature fully redundant class 2 dynamic positioning (DP) and azimuthing podded propulsion. It is also the first ship built where the shipyard has used a containerised electrical control gear solution, developed by German company Siemens.

The ship, which was originally scheduled for delivery toward the end of 2001, is managed by NMA Maritime & Offshore Contractors, which has offices in Houston, USA and Rotterdam, the Netherlands.

NMA says that the fully redundant class 2 DP system is, to oil companies, a very attractive safety feature for the work they require Tai An Kou to undertake.

The ship?s two 4.35MW Siemens Schottel SSP5 pods will, adds NMA, make the vessel extremely manoeuvrable. A company spokesman explains that during voyages the pods will allow the captain to better control the heading and avoid the worst sea conditions. In heavy seas and swell the directional power capability of the pods will help prevent the vessel from turning beam on into waves while optimum course is kept, he adds.

In sea trials the vessel achieved its contractual speed of 15 knots at the load line draught of 7.5m despite what NMA describes as “unfavourable conditions”. At a draught of 5.5m, the vessel achieved over 17 knots says the vessel?s manager. NMA sees this performance as “very encouraging” as the speed will enhance the ship?s weather avoidance capability.

The company has secured work for the vessel through to September. The first job commenced at the end of 2002 and involves transporting a tension leg platform from a Korean shipyard to Indonesia. Subsequent employment involves jobs from Singapore to the US Gulf; the US Gulf to west Africa; Korea to the US Gulf and the US Gulf to west Africa again. Another contract, in December, also involves a US Gulf to west Africa cargo.

One of the jobs involves a float-over deck mating. The process involves the vessel carrying the topsides of an offshore platform inside a steel jacket (the system that connects a platform to the sea floor and extends above the waterline as legs), using its DP system to manoeuvre. Low swell conditions are required. Once in place the vessel is held exactly in position using winches and it is ballasted down so that the topsides deck it is carrying is set down on, in this case, the six legs of the jacket. This is only possible with a semi-submersible if it has DP capability says NMA.

The containerised electrical control gear solution is intended to ease the installation of complex electronics for the shipbuilder. Gunangzhou Shipyard took delivery of a container for Tai An Kou pre-outfitted with converters, transformers and other electrical control equipment. The shipyard simply welded the container into the superstructure and ran cabling from the container to the engine room and switchboard.

Tai An Kou and its sistership Kang Sheng Kou, due early this year, have an open cargo deck measuring 126m by 32.2m, which can be widened to 40m by use of removable sponsons. They can submerge to depths of up to 9m to load cargo up to 16,500t from the stern or side. Working in tandem, the ships will have the ability to take loads up to 30,000t.