leave the assisting to Russian icebreakers. The ships have performed beyond expectations in both level ice up to thick, which can be broken in continuous motion at , and ridges up to deep, which can be penetrated by either allowing the forward-facing propeller to mill (crush) the ice or breaking the ridge apart with the propeller wash. While the vessels have been immobilized occasionally by pack ice, they have been able to free themselves by using the rotating propeller pod to clear the ice around the hull. References 2002 ships Floating production storage and offloading vessels Ships built by Sumitomo Heavy Industries