The old adage of necessity being the mother of invention would certainly seem to apply to the icebreaker industry in Finland: The country depends on marine trade routes through Baltic Sea waters that become covered with pack ice for much of the winter. As a consequence, Finnish companies have designed and built many of the world’s icebreakers and the country continues to pioneer new technologies for navigating through sea ice.
“Our exports are in trouble if we don’t have any icebreakers,” Göran Wilkman, manager, sales and marketing for Helsinki-based Aker Arctic Technology Inc., told an audience at a presentation in Anchorage on Oct. 12.
And with climate change causing changing ice patterns and an increasing prevalence of loose drifting ice, the design of ships that can negotiate polar waters has become more challenging, Wilkman said.
Prudhoe tanker experimentAker Arctic Technology, a leading Finnish icebreaker design and consulting company and a spin-off of shipbuilding company Aker Yards, actually became involved in the initial development of the giant Prudhoe Bay field on Alaska’s North Slope in 1969 when Exxon wanted to test the possibility of exporting Prudhoe Bay oil direct from the slope by oil tanker. Aker Yards designed modifications to the S.S. Manhattan, a U.S. tanker, so that the ship could negotiate the passage through the Canadian islands to the slope. Although the Manhattan did succeed in transiting to and from Prudhoe Bay, the sea route for oil export was deemed impractical and the North Slope oil producers elected instead to build the trans-Alaska pipeline.
But the test tank facility established in Helsinki for the Manhattan project set in motion a program of icebreaker research and development that has continued to the present day and has seen some major evolution in Arctic ship design.
Up through the 1980s the focus was on innovative bow forms for smashing through the ice, Wilkman said. However, despite quite a bit of competition between different companies to discover the best bow design for this purpose, the end results fell short of expectations — specialized icebreaker bows work in calm, restricted water but prove much less effective in passing through ice free areas in open water, where the wave actions and other complications encountered restrict the operability, Wilkman said.
Going backwardBy the late 1980s people were casting around for some new way to improve icebreaker design. Then a surprising but obvious discovery was made: simply reversing the direction of motion of the ship made icebreaking a whole lot easier.
“Conventional icebreakers have been able in certain conditions to move astern in thicker ice than that of running ahead at slow motion, but they were lacking the steerability and possibility to run astern at higher speeds,” Wilkman said.
It turned out that the ship’s propellers up front can carve up the ice and then flush the broken ice out of the ship’s path, enabling the ship to augur its way through an ice field.
Installing bow propellers was abandoned as a design concept long ago because of the complexity and cost of the required propulsion system inside the ship’s hull, Wilkman said. However, the development of diesel-electric drive technology has enabled a design breakthrough in which a diesel engine inside the ship’s hull powers an electrical drive system outside the hull. In the resulting azimuthal propulsion system a pod suspended under the stern of the ship holds the propeller and the electric drive. The pod can be rotated 360 degree, thus allowing the propeller to face in any direction.
In this system, the ship drives forward through open water, with the “azipods” holding the electric drive motors and propellers directed towards the rear. In sea ice, the azipods swivel 180 degrees to point in the opposite direction and the ship goes backwards through the ice.
Going astern may reduce the ice resistance by 50 percent or more and that typically reduces the power required to drive a ship through the ice to 60 percent of what used to be required, Wilkman said.
Negotiating ice ridgesNot only that, a “double acting” vessel that can travel both forwards and backwards can, when going astern, traverse ice conditions that would otherwise prove impassable.
For example, in the late 1990s Aker Arctic Technology was testing icebreaker designs for the Caspian Sea that enabled negotiation of grounded ice ridges 4 to 8 meters (12 to 24 feet) in height, Wilkman said. When trying to move forward through these ridges the bow became stuck on top of the ice, but after turning the ship around to go astern the ship could carve its way through, he said.
Aker Arctic Technology is also engaged in a research project, using models in its test tank facility to evaluate how best to use azimuthal drive icebreakers to protect offshore structures such as drilling rigs from sea ice. In this type of ice management operation, icebreakers typically move in circles through the ice upstream of the fixed structure, Wilkman said. The idea is to break the ice into small pieces, to reduce the force imparted by the ice on the structure.
But, by using an icebreaker with twin azipods it is possible to orient the azipods in different directions and, thus, vary the mode of ice breaking. For example, aiming each azipod somewhat outwards while moving astern through the ice might help widen a channel to clear a broad area. And pointing the azipods in opposite directions fore and aft might help demolish ice ridges or flush ice from localized areas.
The company expects the report from these tests to be available for purchase early 2008.
Aker Arctic Technology has also been forging ahead with new icebreaker designs. The latest concept is an asymmetric icebreaker that looks a bit like a regular ship that somehow got bent out of shape. Armed with three azipods at bow and stern, the icebreaker would move sideways through pack ice, thus clearing a much wider channel than a conventional icebreaker moving forwards or backwards. This strange looking vessel may be effective in cleaning up an oil spill, as well as in clearing channels for other vessels. A 9-megawatt icebreaker of this design could clear a 50-meter wide channel through 1.2-meter-thick ice, Wilkman said.
Cargo vesselsEvolution of the double acting azipod powered icebreaker design led to a realization that purpose-built cargo vessels might also be able to negotiate sea ice using the same principle. In March 2006 a revolutionary new icebreaking container ship built for Russian mining company Norilsk Nickel successfully underwent testing in the Kara Sea and Gulf of Yenisei (on the northern coast of Siberia), Wilkman said.
Aker Arctic Technology has also designed double acting oil tankers for the Baltic for Neste Oil transporting oil from Russia to Finland. In addition, two double acting 70,000-tonnage-dead-weight tankers are scheduled to start shuttle operations in the Pechora Sea in 2008-09 in what Aker Arctic Technology has described as “the world’s first marine Arctic oil export systems,” transporting oil from the offshore Prirazlomnoye oil field and Varandey terminal.
The latest stage of evolution in the development of double acting ships is the design of ice-breaking LNG carriers. In particular, Aker Arctic Technology is researching the feasibility of exporting LNG by double acting LNG carrier from Russia’s Yamal gas field on the east side of the Kara Sea, north of Siberia.
“To get to Yamal you have to go through the Kara Sea and there we have a problem of lots of ice,” Wilkman said. “… It’s a giant ice mass moving back and forth.”
In addition to normal sea ice, the Kara Sea often has ice ridges normally 10 to 15 meters deep, Wilkman said.
All of these cargo vessel designs offer the enticing possibility of shipping freight or petroleum products through sea ice without the need for expensive icebreaker escorts — nearly 40 years after the Prudhoe Bay Manhattan experiment, the concept of operating cargo ships through sea ice appears to be coming of age.