MT Tempera
Tempera at Porvoo oil refinery
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| History | |
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| Name: | Tempera |
| Owner: | SEB Leasing Oy |
| Operator: | Neste Shipping Oy |
| Port of registry: |
Porvoo,  Finland
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| Route: | Primorsk–Porvoo–Naantali |
| Ordered: | 2001 |
| Builder: | Sumitomo Heavy Industries Ltd., Yokosuka, Japan |
| Cost: | 60–70 million euro (estimate) |
| Completed: | August 2002 |
| In service: | 2002– |
| Identification: |
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| Status: | In service |
| General characteristics | |
| Type: | Crude oil tanker |
| Classification: | Lloyd's Register of Shipping |
| Tonnage: | |
| Length: | 252.0 m (826.77 ft) (overall) |
| Beam: | 44.0 m (144.36 ft) |
| Height: | 53.1 m (174 ft) |
| Draught: |
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| Depth: | 22.5 m (74 ft) |
| Ice class: | 1A Super |
| Installed power: |
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| Propulsion: |
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| Speed: |
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| Crew: | 15–20 |
MT Tempera is a Finnish Aframax crude oil tanker operated by Neste Shipping. She was the first ship 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.Tempera and her sister ship Mastera, built in 2003, are used mainly to transport crude oil, year-round, from the Russian oil terminal in Primorsk to Neste Oil refineries in Porvoo and Naantali.
Although icebreaking cargo ships had been built in the past, their hull forms were always compromises between open water performance and icebreaking capability. A good icebreaking bow, designed to break the ice by bending it under the ship's weight, has very poor open water characteristics and is subjected to slamming in heavy weather while a hydrodynamically efficient bulbous bow greatly increases the ice resistance. 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. 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.
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.
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Wikipedia