The Coast Guard has postponed plans to scrap the Seattle-based icebreaker Polar Sea this year. The decision was announced Friday by Sens. Maria Cantwell of Washington and Mark Begich and Lisa Murkowski of Alaska. They say the 399-foot Polar Sea had been scheduled to be dry-docked Monday for the first steps in demolition. It’s sister ship the Polar Star is out of service for a $57 million overhaul at a Seattle shipyard. The United States currently has only one working icebreaker, the Healy. It’s a medium service ship and can’t crunch as much ice as the heavier Polar Sea and Polar Star. Cantwell, Begich and Murkowski say the Polar Sea’s hull is in sound condition and rebuilding the ship would be cheaper than building a new icebreaker.