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Dynamic Positioning of Large Tankers at Sea

AuthorsPinkster, J.A., Nienhuis, U.A.
Conference/JournalOffshore Technology Conference (OTC), Houston, Texas, USA
Date1 mei 1986
In this paper, an unconventional dynamic positioning (DP) system is introduced which is relatively simple from the point of view of the thruster layout and, by virtue of the same thruster layout, automatically positions the vessel in a favorable heading relative to the environment.
This system, which in principle is based on thrusters installed only at the forward (or aft) end of the vessel, possesses automatic weathervaning properties i.e. the DP system itself does not control the heading as this is governed by the environmental conditions. The stable equilibrium heading of the vessel is consistent with the minimum power heading.
The basic principles of the system are explained and results of an extensive series of model tests giving insight in the capabilities of this type of DP system applied to a 200,000 DWT tanker are presented and discussed. The model tests cover a range of realistic sea conditions likely to be regarded as limiting conditions for offshore loading operations.
Such conditions include irregular waves, wind and current. For one test irregular cross-sea conditions combined with wind and current were generated. A number of tests were devoted to investigating stand-by sea conditions and the effects of fast changes in wind direction. The latter tests give insight in the reactions of the DP system to sudden variations in the environmental conditions as can occur, for instance, in cyclone prone areas.
The results of the model tests confirm that it is possible to DP a large tanker in operational conditions using a simple thruster layout and a relatively small amount of installed power.

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