Ships with an ice class have a strengthened hull to enable them to navigate through sea ice. Depending on the class, sea chests, i.e. the openings in the hull for seawater intake, have to be properly arranged in order to avoid blocking up with ice. Most of the stronger classes require several forms of rudder and propeller protection,and strengthened propeller tips are often required.Different ice classes and types exist, depending on the classification societies, but the most often ice class referred to is the Finnish-Swedish ice class.

If hull and machinery are constructed such as to comply with the requirements of different additional class notations POLAR CLASS, then both the hull and the machinery are to be assigned the lower of these additional class notations in the Certificate of Classification. Compliance of hull or machinery with the requirements of a higher additional class notation POLAR CLASS is also to be indicated in the Annex to the Certificate of Classification. The same principle applies to ships having a service notation Icebreaker.

Ships having one of the additional class notationsPOLAR CLASS are to have the hull form and the propulsion power such that the ship can operate independently at continuous speed in the representative ice conditions. For ships not designed to operate independently in ice, such   operational intent or limitations are to be explicitly stated on the Certificate of Classification. Ramming is to be avoided for ships with one of the additional class notations POLAR CLASS.