Ship

:For the online phenomenon of "shipping," see Shipping (fandom).

Measuring ships

One can measure ships in terms of overall length, length of the waterline, beam (breadth), depth (distance between the crown of the weather deck and the top of the keelson), draft (distance between the highest waterline and the bottom of the ship) and tonnage.

Related Topics:
Length - Draft

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A number of different tonnage definitions exist; most measure volume rather than weight and are used when describing merchant ships.

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• Gross tonnage is a measure of the total internal volume of the ship.
• Net tonnage is expresses a merchant vessel's earning capacity and gives the internal capacity of that part of the ship available for cargo or passengers.
• Thames measurement tonnage was used for smaller vessels and worked to a formula: (length - beam) x beam x ½beam / 94
• Displacement tonnage is normally applied to warships and equals the actual weight of a ship complete with crew, fuel, stores and water.
• Light ship tonnage measures the actual weight of the ship with no fuel, no persons, no cargo, no water on board is not usually quoted.
• Deadweight tonnage is the weight of cargo, stores, passengers etc. which when added to the weight of the ship's structure and equipment, will bring the vessel down to her designed waterline.

The word "displacement" arises from the basic physical law, discovered by Archimedes, that the weight of a floating object equates exactly to that of the water which would otherwise occupy the "hole in the water" displaced by the ship.

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In Britain, until the Merchant Shipping Act of 1876, ship-owners could load their vessels until their decks were almost awash, resulting in a dangerously unstable condition. Additionally, anyone who signed onto such a ship for a voyage and, upon realizing the danger, chose to leave the ship, could end up in jail.

Related Topics:
Merchant Shipping Act of 1876 - Jail

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Samuel Plimsoll, a member of Parliament, realised the problem and engaged some engineers to derive a fairly simple formula to determine the position of a line on the side of any specific ship's hull which, when it reached the surface of the water during loading of cargo, meant the ship had reached its maximum safe loading level. To this day, that mark, called the "Plimsoll Mark", exists on ships' sides, and consists of a circle with a horizontal line through the center. Because different types of water, (summer, fresh, tropical fresh, winter north Atlantic) have different densities, subsequent regulations required painting a group of lines forward of the Plimsoll mark to indicate the safe depth (or freeboard above the surface) to which a specific ship could load in water of various densities. Hence the "ladder" of lines seen forward of the Plimsoll mark to this day.

Related Topics:
Samuel Plimsoll - Member of Parliament - Engineer - Formula - Hull - Plimsoll Mark - Circle

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