Double acting ship
[1][2] In the early 1990s, studies conducted by Kvaerner Masa-Yards showed that the ship's open water efficiency is as important factor as its ability to operate in difficult ice conditions in oil transportation from the Russian Arctic to Europe.
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.
[3][4] As a result, the total efficiency of icebreaking ships is 20–40% less than that of good open water vessels of similar size mainly due to the bow form.
[1] 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.
When product tankers Uikku and Lunni were converted to Azipod propulsion in 1993 and 1994, respectively, the result was similar increase in manoeuvrability and icebreaking capability.
[1][3] Model tests conducted by MARC in 1994 showed that a double acting ship equipped with an Azipod propulsion unit could break through ice ridges in continuous motion instead of ramming like conventional icebreakers.
[5] The Norwegian Coast Guard operates a double acting offshore patrol vessel KV Svalbard, built in 2002 and equipped with two 5 MW Azipod propulsion units.
[11] The 25 MW diesel-electric line icebreaker ordered by Rosmorport from Baltic Shipyard under the project name LK-25, Viktor Chernomyrdin, will be capable of proceeding continuously both ahead and astern in compact ice field up to 2 metres (6.6 ft) thick with a 20-centimetre (7.9 in) snow cover at 2 knots (3.7 km/h; 2.3 mph).
The vessels, currently under construction and scheduled to be delivered in 2017, represent a further development of the Finnish icebreaker Polaris with capability of breaking 2-metre (7 ft) ice in both ahead and astern directions.
The Polar Class 3 vessel, fitted with two azimuth thrusters, will be able to break level ice with a thickness of 1.5 metres (5 ft) and a snow cover of 20 centimetres (8 in).
[22][23] The tankers, equipped with two Azipod units, are capable of bow loading and independent operation in level ice up to 1.2 meters in thickness.
[22] In March 2010 Norilsk Nickel placed an order for an Arc7 ice class oil tanker derivate of its double acting arctic cargo ships at Nordic Yards in Wismar.
[27] The Arctic LNG carriers, fitted with three 15 MW ABB Azipod propulsion units, are the largest icebreaking vessels in the world with an independent ice-going capability in level ice up to 2.1 metres (6.9 ft) in thickness.
[29] In July 2014, Samsung Heavy Industries received a $440 million order for three ice class Arc7 shuttle tankers for the Russian shipping company Sovcomflot.
[18] Four additional ships, with an option for fifth, were ordered in 2007 from Aker Yards's shipyards in Germany, with deliveries in the second half of 2008 (Monchegorsk, Zapolyarny and Talnakh) and early 2009 (Nadezdha).
[25] On 22 March 2011 Gaiamare, a subsidiary of Meriaura, ordered a 115-metre (377 ft) double acting multipurpose cargo ship designed especially for demanding projects such as transporting wind turbines to offshore installations.
