The icebreaking tanker was built to transport crude oil year-round from the Russian oil terminal in Primorsk to Neste Oil refineries in Porvoo and Naantali.
A double acting ship is a type of icebreaking ship designed to run ahead in open water and thin ice, but turn around and proceed astern (backwards) in heavy ice conditions. In this way, the ship can operate independently in severe ice conditions without icebreaker assistance but retain better open water performance than traditional icebreaking vessels.
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.
The double acting tanker is 252.0 meters long overall and 237.59 meters between perpendiculars. The moulded breadth and depth of her hull are 44.0 meters and 22.5 meters, respectively, and from keel to mast she measures 53.1 meters.
In September 2021, Mastera was transferred to the Norwegian International Ship Register. In January 2022, she was renamed Mikines and reflagged to Liberia. In March 2022, the 19-year-old Mikines appeared on list of tonnage sold for demolition, but has since resumed trading and was renamed Alma in June 2022.
According to Wikipedia