Accumulations of ice on a vessel may lead to serious stability problems. Substantial icing can occur when temperatures are between -3 and -8 degrees Celsius with winds 16–30 knots. The danger increases with colder temperatures or stronger winds.
Freezing sea spray is the most common and the most hazardous form of icing. Spray blown by winds can cause heavy icing on a vessel, producing a heavy list. Freezing spray usually occurs when the air temperature is less than -2 degrees Celsius, and the water is less than 5 degrees Celsius. Freezing spray warnings are included in marine weather forecasts.
With freezing rain, a film of ice forms over the decks, railings and stairways. This form of icing is the least likely to cause stability problems, but it can be a serious hazard for the crew moving on deck.
A similar glaze of ice can be caused by sea smoke. Sea smoke forms when very cold air moves over warmer water, and it can freeze on contact with the vessel. It is not usually a severe problem, but if the sea smoke is very dense substantial ice may accumulate.