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The acronym DAT means Double Acting Tanker, a concept where the ship is designed to run astern in heavy ice conditions while remaining hydro-dynamically efficient for ahead propulsion in open water conditions. Two large aframax DATs - 106.000 DWT each - has been delivered by Sumitomo Heavy Industries to Fortum Oil & Gas OY. They are the first crude carriers built according to the DAT principle and also the first using pod propulsion from the beginning. They will also be the world's largest crude carriers with ice-class 1A super and are primarily intended for year-round transportation of north-sea crude to Fortum's refineries in the Gulf of Finland. The ships were appointed “Ship of the year” in Japan 2003. SSPA was contracted by Sumitomo Heavy Industries to perform model tests. A comprehensive open water model test program was used to investigate aspects of resistance and propulsion, manoeuvring and cavitation performance. As the ship is designed to operate both in ahead and astern condition for prolonged periods of time most tests were performed both ahead and astern. Also a simulation study of dynamic positioning at buoy- or FPSO-loading was made by SSPA. Comprehensive tests of the ships performance in ice were performed in the ice-tank at MARC (Masa-Yards Artic Research Centre). The eight-month model testing and development campaign resulted in a ship with excellent propulsion and manoeuvring performance, especially with regard to the high ice class. Sea trials carried out with the first ship in August 2002 confirmed the results of the model test. Interesting experiences of the model test campaign and comparison between model test and sea trial results are presented as well as some examples of single point mooring simulations. |
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