The displacement or displacement tonnage of a ship is its weight. As the term indicates, it is measured indirectly, using Archimedes' principle, by first calculating the volume of water displaced by the ship, then converting that value into weight. Traditionally, various measurement rules have been in use, giving various measures in long tons.[1] Today, tonnes are more commonly used.
Load lines, by showing how low a ship is sitting in the water, make it possible to determine displacement.
Ship displacement varies by a vessel's degree of load, from its empty weight as designed (known as "lightweight tonnage"[2]) to its maximum load. Numerous specific terms are used to describe varying levels of load and trim, detailed below.
Ship displacement should not be confused with measurements of volume or capacity typically used for commercial vessels and measured by tonnage: net tonnage and gross tonnage.
Shipboard stability computer programs can be used to calculate a vessel's displacement.
The process of determining a vessel's displacement begins with measuring its draft.[3] This is accomplished by means of its "draft marks" (or "load lines"). A merchant vessel has three matching sets: one mark each on the port and starboard sides forward, midships, and astern.[3] These marks allow a ship's displacement to be determined to an accuracy of 0.5%.[3]
The draft observed at each set of marks is averaged to find a mean draft. The ship's hydrostatic tables show the corresponding volume displaced.[4] To calculate the weight of the displaced water, it is necessary to know its density. Seawater (1,025 kg/m3) is more dense than fresh water (1,000 kg/m3);[5] so a ship will ride higher in salt water than in fresh. The density of water also varies with temperature.
Devices akin to slide rules have been available since the 1950s to aid in these calculations. Presently, it is done with computers.[6]
In this 1940 photo, USS Aaron Ward, left, and USS Abel P. Upshur are destroyers of comparable size, but because the latter is more heavily loaded, it sits lower, displacing more water.
There are terms for the displacement of a vessel under specified conditions:
Loaded displacement
Loaded displacement is the weight of the ship including cargo, passengers, fuel, water, stores, dunnage and such other items necessary for use on a voyage. These bring the ship down to its "load draft",[8] colloquially known as the "waterline".
Full load displacement and loaded displacement have almost identical definitions. Full load is defined as the displacement of a vessel when floating at its greatest allowable draft as approved by the load line assigning authority which is either the flag state (USCG etc) or a classification society (and designated by its "waterline").[9] Warships have full load condition established through the Naval design process, and are exempt from commercial requirements laid out by flag state laws.[9]
Light displacement
Light displacement (LDT) is defined as the weight of the ship excluding cargo, fuel, water, ballast, stores, passengers, crew, but with water in boilers to steaming level.[8]
Normal displacement
Normal displacement is the ship's displacement "with all outfit, and two-thirds supply of stores, ammunition, etc., on board."[10]
Standard displacement
Standard displacement, also known as "Washington displacement", is a specific term defined by the Washington Naval Treaty of 1922.[11] "It is the displacement of the ship complete, fully manned, engined, and equipped ready for sea, including all armament and ammunition, equipment, outfit, provisions and fresh water for crew, miscellaneous stores, and implements of every description that are intended to be carried in war, but without fuel or reserve boiler feed water on board."[11]
Gallery
A floating ship's displacement Fp and buoyancy Fa must be equal.
Greek philosopher Archimedes having his famous bath, the birth of the theory of displacement
A ship's hydrostatic curves. Lines 4 and 5 are used to convert from mean draft in meters to displacement in tonnes (table in Spanish).
^Dinsmore, Ben (16 May 2011). . The Maritime Site. Archived from the original on 29 May 2011. Retrieved 14 February 2018.{{cite web}}: CS1 maint: unfit URL (link)
^ abConference on the Limitation of Armament, 1922. Ch II, Part 4.
Bibliography
Dear, I.C.B.; Kemp, Peter (2006). Oxford Companion to Ships and the Sea (Paperback ed.). Oxford: Oxford University Press. ISBN0-19-920568-X.
George, William E. (2005). Stability & Trim for the Ship's Officer. Centreville, Md: Cornell Maritime Press. ISBN0-87033-564-2.
Hayler, William B. (2003). American Merchant Seaman's Manual. Cambridge, Md: Cornell Maritime Press. ISBN0-87033-549-9..
Turpin, Edward A.; McEwen, William A. (1980). Merchant Marine Officers' Handbook (4th ed.). Centreville, MD: Cornell Maritime Press. ISBN0-87033-056-X.
Navy Department (1942). "Nomenclature of Naval Vessels". history.navy.mil. United States Navy.
Military Sealift Command. . MSC Ship Inventory. United States Navy. Archived from the original on 2007-02-05. Retrieved 2008-03-24.
MLCPAC Naval Engineering Division (2005-11-01). "Trim and Stability Information for Drydocking Calculations". United States Coast Guard. Retrieved 2008-03-24.
United States of America (1922). "Conference on the Limitation of Armament, 1922". Papers Relating to the Foreign Relations of the United States: 1922. Vol. 1. pp. 247–266.
United States Naval Institute (1897). Proceedings of the United States Naval Institute. United States Naval Institute. Retrieved 2008-03-24.
January 07, 2023
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The displacement or displacement tonnage of a ship is its weight As the term indicates it is measured indirectly using Archimedes principle by first calculating the volume of water displaced by the ship then converting that value into weight Traditionally various measurement rules have been in use giving various measures in long tons 1 Today tonnes are more commonly used Load lines by showing how low a ship is sitting in the water make it possible to determine displacement Ship displacement varies by a vessel s degree of load from its empty weight as designed known as lightweight tonnage 2 to its maximum load Numerous specific terms are used to describe varying levels of load and trim detailed below Ship displacement should not be confused with measurements of volume or capacity typically used for commercial vessels and measured by tonnage net tonnage and gross tonnage Contents 1 Calculation 2 Definitions 2 1 Loaded displacement 2 2 Light displacement 2 3 Normal displacement 2 4 Standard displacement 3 Gallery 4 See also 5 References 5 1 BibliographyCalculation Edit Shipboard stability computer programs can be used to calculate a vessel s displacement The process of determining a vessel s displacement begins with measuring its draft 3 This is accomplished by means of its draft marks or load lines A merchant vessel has three matching sets one mark each on the port and starboard sides forward midships and astern 3 These marks allow a ship s displacement to be determined to an accuracy of 0 5 3 The draft observed at each set of marks is averaged to find a mean draft The ship s hydrostatic tables show the corresponding volume displaced 4 To calculate the weight of the displaced water it is necessary to know its density Seawater 1 025 kg m3 is more dense than fresh water 1 000 kg m3 5 so a ship will ride higher in salt water than in fresh The density of water also varies with temperature Devices akin to slide rules have been available since the 1950s to aid in these calculations Presently it is done with computers 6 Displacement is usually measured in units of tonnes or long tons 7 Definitions Edit In this 1940 photo USS Aaron Ward left and USS Abel P Upshur are destroyers of comparable size but because the latter is more heavily loaded it sits lower displacing more water There are terms for the displacement of a vessel under specified conditions Loaded displacement Edit Loaded displacement is the weight of the ship including cargo passengers fuel water stores dunnage and such other items necessary for use on a voyage These bring the ship down to its load draft 8 colloquially known as the waterline Full load displacement and loaded displacement have almost identical definitions Full load is defined as the displacement of a vessel when floating at its greatest allowable draft as approved by the load line assigning authority which is either the flag state USCG etc or a classification society and designated by its waterline 9 Warships have full load condition established through the Naval design process and are exempt from commercial requirements laid out by flag state laws 9 Light displacement Edit Light displacement LDT is defined as the weight of the ship excluding cargo fuel water ballast stores passengers crew but with water in boilers to steaming level 8 Normal displacement Edit Normal displacement is the ship s displacement with all outfit and two thirds supply of stores ammunition etc on board 10 Standard displacement Edit Standard displacement also known as Washington displacement is a specific term defined by the Washington Naval Treaty of 1922 11 It is the displacement of the ship complete fully manned engined and equipped ready for sea including all armament and ammunition equipment outfit provisions and fresh water for crew miscellaneous stores and implements of every description that are intended to be carried in war but without fuel or reserve boiler feed water on board 11 Gallery Edit A floating ship s displacement Fp and buoyancy Fa must be equal Greek philosopher Archimedes having his famous bath the birth of the theory of displacement A ship s hydrostatic curves Lines 4 and 5 are used to convert from mean draft in meters to displacement in tonnes table in Spanish See also Edit Transport portalNaval architecture Hull watercraft Hydrodynamics TonnageReferences Edit Ship Tonnage Explained Displacement Deadweight Etc GG Archives www GGArchives com Retrieved 2019 01 14 Dinsmore Ben 16 May 2011 A Guide to Understanding Ship Weight and Tonnage Measurements The Maritime Site Archived from the original on 29 May 2011 Retrieved 14 February 2018 a href Template Cite web html title Template Cite web cite web a CS1 maint unfit URL link a b c George 2005 p 5 George 2005 p 465 Turpin and McEwen 1980 George 2005 p 262 Otmar Schauffelen 2005 Chapman Great Sailing Ships of the World Hearst Books p xix a b Military Sealift Command a b Department of the Navy 1942 United States Naval Institute 1897 p 809 a b Conference on the Limitation of Armament 1922 Ch II Part 4 Bibliography Edit Dear I C B Kemp Peter 2006 Oxford Companion to Ships and the Sea Paperback ed Oxford Oxford University Press ISBN 0 19 920568 X George William E 2005 Stability amp Trim for the Ship s Officer Centreville Md Cornell Maritime Press ISBN 0 87033 564 2 Hayler William B 2003 American Merchant Seaman s Manual Cambridge Md Cornell Maritime Press ISBN 0 87033 549 9 Turpin Edward A McEwen William A 1980 Merchant Marine Officers Handbook 4th ed Centreville MD Cornell Maritime Press ISBN 0 87033 056 X Navy Department 1942 Nomenclature of Naval Vessels history navy mil United States Navy Military Sealift Command Definitions Tonnages and Equivalents MSC Ship Inventory United States Navy Archived from the original on 2007 02 05 Retrieved 2008 03 24 MLCPAC Naval Engineering Division 2005 11 01 Trim and Stability Information for Drydocking Calculations United States Coast Guard Retrieved 2008 03 24 United States of America 1922 Conference on the Limitation of Armament 1922 Papers Relating to the Foreign Relations of the United States 1922 Vol 1 pp 247 266 United States Naval Institute 1897 Proceedings of the United States Naval Institute United States Naval Institute Retrieved 2008 03 24 Retrieved from https en wikipedia org w index php title Displacement ship amp oldid 1127394335, wikipedia, wiki, book, books, library,
