Pack ice around Iceland was becoming a threat to navigation.

冰岛周围的浮冰一度成为船舶航行的威胁。

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Navigation was confined to shallow vessels, tricky enough even in the few summer months when the river was free of ice.

航行船只局限于小船，即使在短短夏季数月的无冰期，通行起来也足够困难。

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But even if the ice melts as fast as shippers hope (and scientists fear), navigation is likely to demand strengthened hulls, higher insurance and extra training for crews, all adding to the costs.

但是即使冰融化得象航运者们希望的那样快(科学家们担心的)，航行可能需要加固船体、更高的保险和对全体船员附加的训练，所有的都增加了开销。

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The exercises train U.S. submarine crews to deal with craggy ice keels that extend 20 to 50 feet into the water, and varying salinity levels that complicate communications and navigation under the ice cap.

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But even if the ice melts as fast as shippers hope (and scientists fear), navigation is likely to demand strengthened hulls, higher insurance and extra training for crews, all adding to the costs.

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The button layout is also different, as it uses the standard three capacitive buttons for navigation instead of the special tablet-specific menus found in Honeycomb and Ice Cream Sandwich.

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