Underwater Mountable Thrusters Preferred for Deepwater Drillship

New Wave Media

June 15, 2013

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Azimuth Thrusters have been propelling deepwater drillships for a number of years now. Not only do they propel the drillships from ports to their drilling stations but also undertake the vital task of maintaining the ship’s position during drilling operations. As most people know deepwater drillships do not anchor but maintain dynamic positioning through the use of groups of thrusters.

Depending on the size of the drillship, these may be grouped in threes or fours, and are always positioned fore and aft on traditional drillships. These dispositions vary in semi-submersible drillers and cylindrical drillers such as those developed and used by Sevan Drilling. In both cases the thrusters are used to propel the rig and for dynamic positioning during drilling operations, therefore large reduction ratios and big slow turning propellers are preferred by major thruster manufacturer Rolls Royce, to give maximum thrust to the ships.

Rolls Royce is is currently the world leader in the supply of drivers for drillships, with about 70% share of this market. The drillships operate mostly in O&G wells located on the coast of Brazil, on the west coast of Africa and the Gulf of Mexico. With Brazil currently being the location where most deepwater drillships are in operation and where most new drillships being built are headed to.Rolls Royce has very recently been awarded a contract to supply its underwater removable thrusters to Transocean a world leader in deepwater drilling, it’s notable that this was the 100th drillship to feature Rolls-Royce propulsion.

The robust, heavy-duty Rolls Royce UUC azimuth thruster specifically designed for extended operations on offshore rigs and drillships is capable of underwater mounting and demounting without the need to drydock using a specially developed lifting technique, and a unique sealing and locking device.

There are two alternative ways to connect the lifting wires: Connecting inside the ship to the thruster flange or externally to the lifting lugs on the thruster flange. The former is typical on the drill ships and the latter on the Semi Submersibles. These models come in a power range of 3,000kw to 6,500kw. This is a significant advantage as it greatly reduces downtime since a faulty thruster can be removed and a replacement installed in a matter of hours, if a replacement is at hand.

Even with no replacement immediately at hand it would still take much less time for a replacement to be shipped from the warehouse to the drilling location, than to have to bring the drillship to drydock and back. This, along with robustness and a proven track record of reliability, is the main reason that it is highly probable that all drillships to be ordered by Petrobras in the near future will be using these Rolls Royce UUC thrusters.

Paschoa, Claudio
Claudio Paschoa is Marine Technology Reporter's correspondent in Brazil.
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