Source:
BBCA number of ships, including ferries with thousands of passengers on board, have become stuck in ice in the Baltic Sea, officials say.
The ferries are stranded in the waters between Stockholm and the Aland Islands, while cargo boats are stuck in the Bay of Bothnia.
...
"The ice wouldn't usually be a problem for the merchant ships, the problem now is that it's very windy, about 20 metres per second," Jonas Lindvall, controller of the ice-breaking unit at the Swedish maritime authorities, told Radio Sweden.
"That means that the ice is moving rapidly, there are lots of ridges with ice that's making it problematic for the ships, so they need help from the ice breakers," the controller said.
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http://news.bbc.co.uk/1/hi/world/europe/8550687.stm
20 m/s = 45 mph