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MT Mastera
MT ''Mastera'' is a Finnish Aframax crude oil tanker operated by Neste Shipping. She and her sister ship, ''Tempera'', are the first ships to utilize the double acting tanker (DAT) concept, developed by Aker Arctic, in which the vessel is designed to travel ahead in open water and astern in severe ice conditions.〔〔(Fortum toi Itämerelle ketterän öljytankkerin ), Tekniikka & Talous, 2002-11-14〕 The two icebreaking tankers are used to transport crude oil year round from the Russian oil terminal in Primorsk to Neste Oil refineries in Porvoo and Naantali.〔
== Concept ==
(詳細はslamming in heavy weather while a hydrodynamically efficient bulbous bow greatly increases the ice resistance.〔Kujala, P and Riska, K: Talvimerenkulku (TKK-AM-13). Department of Applied Mechanics, Helsinki University of Technology, 2010.〕 However, already in the late 1800s captains operating ships in icebound waters discovered that sometimes it was easier to break through ice by running their vessels astern. This was because the forward-facing propellers generated a water flow that lowered the resistance by reducing friction between the ship's hull and ice.〔Aker Arctic Technology Inc.: (Icebreaking Supply Vessels Arcticaborg and Antarcticaborg ). 〕 These findings resulted in the adoption of bow propellers in older icebreakers operating in the Great Lakes and the Baltic Sea, but as forward-facing propellers have a very low propulsion efficiency and the steering ability of a ship is greatly reduced when running astern, it could not be considered a main operating mode for merchant ships.〔Juurmaa, K et al.: (New ice breaking tanker concept for the arctic (DAT) ). Kvaerner Masa-Yards Arctic Technology, 1995.〕〔Juurmaa, K et al.: The development of the new double acting ships for ice operation. Kvaerner Masa-Yards Arctic Technology, (2001 ) and (2002 ).〕
For this reason it was not until the development of electric podded propulsion, ABB's Azipod, that the concept of double acting ships became feasible. The superiority of podded propulsion in icebreaking merchant ships, especially when running astern, was proved when Finnish product tankers ''Uikku'' and ''Lunni'' were converted to Azipod propulsion in 1993 and 1994, respectively. Even though the ships were originally designed with icebreaking capability in mind, after the conversion ice resistance in level ice when running astern was only 40% of that when breaking ice ahead despite the ships being equipped with an icebreaking bow and not designed to break ice astern.〔〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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