New Icepod thruster favoured for Caspian and Alaskan operations
Propulsion solutions for navigation in ice have been augmented by Wärtsilä’s development of a steerable, pulling thruster designed to 1A Super Ice Class or higher standards, known as the Icepod. David Tinsley explains.
Currently available in the 1,750kW and 2,500kW power classes, the 360° rotatable unit allows for astern icebreaking operations, while offering the requisite open-water efficiency when propelling the ship forward.
Compared to a conventional, steerable thruster for open water conditions, the can-mounted Icepod has a larger nacelle size but a smaller, faster running propeller. The open, fixed-pitch propeller is actively used in ice milling and flushing in astern mode.
Although the Baltic region and the Russian Arctic constitute primary markets for such propulsors, Wärtsilä’s initial Icepod contracts entail newbuild applications to an Alaskan research ship and two Caspian Sea support vessels.
The thruster structure and propeller are engineered for the high ice loadings borne when running both astern and forward in level ice, and when encountering large ice blocks and penetrating ice ridges stern-first. Icepod has been conceived with special consideration of shallow draught requirements and of installation space limitations. The Z-drive configuration permits a low-height, inboard thruster room, maximising hull volume utilisation or working deck area. The rigid mounting can is shaped to form an integral part of the icebreaking aftship section.
An additional design consideration was the particular challenges of dealing with technical problems when operating in remote areas, with the result that the thruster can be removed or exchanged without the use of a drydock or habitat. Given the particular environmental sensitivity of ice-laden regions, a four-lip seal has been adopted to prevent oil leakage, water ingress and oil contamination. The high-end seal system is well suited to shallow draught conditions.
The first Icepod thrusters were delivered in the opening quarter of 2012 for installation in a new 80m US oceanographic vessel under construction at the Marinette Marine yard in Wisconsin. Owned by the National Science Foundation and operated by the University of Alaska Fairbanks, the Sikuliaq will be based at the university’s Seward Marine Center and is scheduled to start her scientific duties in 2014.
Ice strengthening and the special ice propulsion arrangements will allow the ship to work safely in moderate seasonal ice, operating over a longer period than previously possible in the North Pacific Ocean, Gulf of Alaska, and the Bering, Chukchi and Beaufort Seas. This will increase the scope for investigating various ecosystem issues, including the response of Alaska’s fisheries to climate change.
Sikuliaq has been specified with two can-mounted Icepod 2500 main thrusters. Both the vessel and her 2,500kW thrusters will meet PC5 ice class criteria, under ABS classification.
Subsequent shipments of Icepods have been made to the Netherlands, for a newbuild project at Groningen’s Royal Niestern Sander yard entailing two 68m icebreaking support vessels tailored to the requirements of year-round service to the Caspian Sea oil and gas industry. Sanaborg, the first of the pair ordered by Wagenborg Offshore, was handed over in August 2012 and completion of second-of-class Serkeborg was anticipated in September.
Each vessel is powered by two Caterpillar 3516C diesel gensets producing 2,000kWe, with drive to two Icepods. Wagenborg’s requirements, based on operational experience in the north Caspian Sea since 1998, were shaped by the need for ice milling in environmentally sensitive, shallow waters. The company’s 1998-built, Caspian-deployed support ships Arcticaborg and Antarcticaborg are each fitted with two 1,620kW ABB Azipod units, and were the first of their type to encapsulate Aker Arctic’s ‘double-acting ship’ (DAS) concept.
Wärtsilä has indicated that it is ready to expand its Icepod offering beyond the 1,750kW and 2,500kW types in accordance with customer needs.
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