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An oil tanker that turns into an icebreaker is being patented by the
Norwegian State Oil Company (WO 98/46477). The tanker has the usual long
barge-like body—but instead of being driven by an engine and propeller, it
is pushed along by a tugboat that snuggles into its stern. If there is ice ahead
that might damage the hull, the tug unhitches from the stern, chugs round to the
front and starts pulling the tanker along instead. The bows of the tug act as an
icebreaker.