Ocean waves and pack ice

Extract

The general effect of pack ice in calming down waves and swell is well known. In the section on ice navigation in the Arctic Pilot, the abrupt smoothing of the sea and the gradual lessening of ordinary ocean swell are noted as good indications of pack ice to windward. In discussing the formation of slush, the Arctic Pilot says “The formation of slush damps down any swell…”, while in discussing the method of entry of a ship into pack ice, the following warning is given: “If the wind is blowing, or a current setting from the open water on to the ice edge, this will be more compact, with a more or less clear-cut outline. On the other hand, if the wind is blowing off the ice, or a current is setting from it towards the open water, the ice edge will be more or less broken and indistinct. It is therefore better to enter the ice from up wind, if possible. When it is necessary to enter the ice down wind, very great care must be exercised on account of the compactness of the edge and the movement of the ice due to waves, which may cause heavy blows against the hull. A combination of these two factors may render the entry difficult, the surge of the ice being especially dangerous if considerable.”