Ice accretion is ice that gathers on the external surfaces of a ship. Ice forms in near-freezing temperatures due to water spray, green water being shipped on decks, and precipitation. The quick removal of ice is important, as ice on the superstructure raises the VCG of the vessel, decreasing the vessels stability and risking capsize.
Ice accumulation can be reduced by running steam or heated water through railings, by avoiding areas of freezing fog, ice fog, or freezing rain, or through a reduction of speed in freezing conditions (to limit spray). Once accumulated, ice is generally removed by crew members by physical force: i.e., using large hammers or similar to break up the ice, and manually throwing ice overboard.
In order to determine what effect this will have on stability Transport Canada has set forth guidelines for icing (see external references). Different surfaces on the vessel are considered as gathering ice at different rates, depending on their location and their distance above the waterline. Areas and projected areas of ice-accumulating structures (primarily those which which trap or drip instead of sheet water) are used with accumulation rates to determine an overall ice load, LCG and VCG. This weight is then added to the stability booklets conditions of load to evaluate adequate reserve stability.