Efficiency has always been key in the design of container ships. While containers may be carried on conventional break-bulk ships, cargo holds for dedicated container ships are specially constructed to speed loading and unloading, and to efficiently keep containers secure while at sea. A key aspect of container ship specialization is the design of the hatches, the openings from the main deck to the cargo holds. The hatch openings stretch the entire breadth of the cargo holds, and are surrounded by a raised steel structure known as the hatch coaming. On top of the hatch coamings are the hatch covers. Until the 1950s, hatches were typically secured with wooden boards and tarpaulins held down with battens. Today, some hatch covers can be solid metal plates that are lifted on and off the ship by cranes, while others are articulated mechanisms that are opened and closed using powerful hydraulic rams.
Another key component of dedicated container-ship design is the use of cell guides. Cell guides are strong vertical structures constructed of metal installed into a ship's cargo holds. These structures guide containers into well-defined rows during the loading process and provide some support for containers against the ship's rolling at sea. So fundamental to container ship design are cell guides that organizations such as the United Nations Conference on Trade and Development use their presence to distinguishing dedicated container ships from general break-bulk cargo ships.
A system of three dimensions is used in cargo plans to describe the position of a container aboard the ship. The first coordinate is the row, which starts at the front of the ship and increases aft. The second coordinate is tier, with the first tier at the bottom of the cargo holds, the second tier on top of that, and so forth. The third coordinate is the slot. Slots on the starboard side are given odd numbers and those on the port side are given even numbers. The slots nearest the centerline are given low numbers, and the numbers increase for slots further from the centerline.
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Famous quotes containing the words holds and/or cargo:
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—Melinda M. Marshall (20th century)
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