Floe

A floe is any contiguous piece of sea ice 20 m or more across, the basic unit of pack ice in the WMO Sea-Ice Nomenclature (WMO No. 259). Floes are graded by horizontal extent: small (20 to 100 m), medium (100 to 500 m), big (500 to 2,000 m), vast (2 to 10 km), and giant (over 10 km); pieces under 20 m are ice cake or brash. Floe size sets a ship’s path through the pack and the impact loads on the hull, since a vessel skirts, deflects, or rams a floe by class. Ice charts record dominant and secondary floe size next to concentration and stage of development.