One of the key enabling technologies involved with modern Arctic-going vessels is the azimuth thruster. Azimuth thrusters are favored by the cruise industry because they can be tilted at different angles, which reduces propeller-induced vibrations and shock loads on a ship’s hull, allowing passengers to enjoy a quieter voyage. But in the Arctic, azimuth thrusters have been proven to be effective at moving large vessels through ice with greater ease and efficiency than shaft-driven propellers. Because the propeller blades are in front of the pod, where the electric-driven motor is located, they resemble the propellers on the nose of an aircraft and perform much in the same manner by pushing, or pulling, the vessel through the water.
In the 1980s, nearly 30 years after it was first invented as a way to replace propeller shafts and rudders, ABB Group developed the first azimuth thrusters, branded by the company as Azipods, with an electric motor inside the pod. The company is now the leading maker of the technology and has delivered units requiring up to 16 MW for the icebreaker market. Evidence that the technology is gaining greater acceptance in the offshore industry is probably most apparent offshore Russia’s Sakhalin Island, where nearly every vessel operating in support oil and gas operations uses azimuth propulsion. “The old vessels with shaft drives have become obsolete there,” said ABB’s icebreaker specialist, Torsten Heideman. “It is only in Alaska where they have not adopted this technology yet, and as we remember, we saw some scary moments there in December of 2012,” he said, in reference to the grounding of a Shell-owned drilling rig.
As a traditional icebreaker’s hull breaks up ice, it slides down under the hull and along the length of a ship creating friction and increasing the power required to move forward. With azimuth thrusters, a ship can run astern, or backward, very efficiently as the ice is flushed around the hull, which in turn reduces the friction to a large degree. The blades on the propellers are strong enough to “chew” through meter-thick chunks and may reduce the dependency on a heavy icebreaker in light ice conditions. Powered by a diesel-electric system that eliminates the need for a long shaft and large engines to turn it, azimuth propulsion also provides ship designers and builders with greater flexibility in how they arrange the engineering section of the underdeck.
