What is ice strengthening?
People sometimes ask what is meant by an ice strengthened hull and how is it achieved. Ice strengthening allows the ship to operate in light ice known as nilas which is less than 10cm thick. Typically this would be designed into ships likely to operate in polar waters such as cruise ships, warships and of course fishery research vessels. This is different from icebreakers which are made of much sterner stuff.
How is ice strengthening achieved?
To understand ice strengthening you first have to have knowledge of ship construction. As you may know a ship is built from the keel up. Explorer’s keel is formed from 8″x2″ (20.32cm x 5.08cm) flat steel bar. Frames are attached to the keel. These are analogous to ribs on a mammal. Explorer has 112 frames numbered from frame 1 at the sternpost to 108 at the bow. Four frames are located aft of the sternpost. The hull plating is riveted to these frames
The illustration taken from the profile and deck drawing used by the builders during construction Note the frame spacing of 21″ (53.34cm). This reduces to 20.5″ (52.07cm) in way of the gallows.
As can be seen from this illustration the frame spacing reduces to 17.5″ (39.37cm) around the bow, the part of the ship most likely to contact ice. The side plating of the ship is fitted in what are called strakes. defined alphabetical from A on the keel to H on the bulwarks.
This illustration shows the plate thickness as being 0.44″ to 0.4″ increasing to 0.54″ by the gallows. (1.1176cm, 1.016cm and 1.3716cm respectively). Unfortunately for some reason the thickness of the bow plating is in the shell expansion drawing which is not in the society’s possession.
Scantlings is the term used in shipbuilding for the dimensions of structural elements of a ship. Here are the Explorer’s scantlings from the ship’s midsection drawing for any geeks who are interested.