# Displacement (ship)

Displacement (ship)
As weight is added to a ship, it submerges. Designated displacement is the ship's weight when fully loaded and submerged to her load lines.

A ship's displacement is its weight[1] at any given time, generally expressed in metric tons or long tons. The term is often used to mean the ship's weight when it is loaded to its maximum capacity. A number of synonymous terms exist for this maximum weight, such as loaded displacement, full load displacement and designated displacement.[2] Displacement is a measurement of weight, and should not be confused with similarly named measurements of volume or capacity such as net tonnage, gross tonnage, or deadweight tonnage.

The word displacement refers to the weight of the water that the ship displaces while floating.[3] Another way of thinking about displacement is the amount of water that would spill out of a completely filled container were the ship to be placed into it. A floating ship always displaces an amount of water of the same weight as the ship.[3]

The density (weight per unit of volume) of water can vary. For example, the average density of seawater at the surface of the ocean is 1025 kg/m³ (10.25 lb/ga, 8.55 lb/US gallon), fresh water on the other hand has a density of about 1000 kg/m³ (10.00 lb/ga, 8.35 lb/US gallon).[2] Consider a 100-ton ship passing from a saltwater sea into a freshwater river. It always displaces exactly 100 tons of water, but it has to displace a greater volume of fresh water to amount to 100 tons. Therefore it would sit slightly lower in the water in the freshwater river than it would in the saltwater sea.

It can be useful to know a ship's displacement when it is unloaded or partially loaded. Terms for these measurements include light displacement, standard displacement, and normal displacement. These terms are defined fully below.

## Calculation

Shipboard stability programs are often used to calculate a ship's current displacement.

The traditional method for determining a ship's actual displacement is by use of draft marks.[4] A merchant vessel has six sets of draft marks: forward, midships, and astern on both the port and starboard sides.[4] These drafts can allow the determination of a ship's displacement to an accuracy of 0.5%.[4] First, the individual drafts are averaged to find a mean draft.[5] Then the mean draft is entered into the ship's hydrostatic tables, giving a displacement.[6]

Computers have been used to assist in hydrostatic calculations, such as determining displacement, since the 1950s.[7] The first were mechanical computers, similar to slide rules which could convert cargo levels to values such as deadweight tonnage, draft, and trim.[7] Since the 1970s, personal computer-based programs have been developing to meet these needs.[7]

## Displacement under special conditions

A number of measurements of displacement are defined when the ship is in a special state, such as when it is completely full or completely empty. These special types of displacement are discussed below.

Full load displacement is defined as the displacement of a vessel when floating at her greatest allowable draft as established by the classification societies.[8] For warships, an arbitrary full load condition is established.[8] Deep load condition means full ammunition and stores, with most available fuel capacity used.

Loaded displacement is defined as the weight of the ship including cargo, passengers, fuel, water, stores, dunnage and such other items necessary for use on a voyage, which brings the ship down to her load draft.[9]

### Standard displacement

The standard displacement, also known as Washington disp, is a term defined in the Washington Naval Treaty.[10] It is defined as 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.[10] The omission of fuel and water was to avoid penalizing the British who had greater global reach and required higher fuel loads.

### Light displacement

Light displacement is defined as the weight of the ship excluding cargo, fuel, ballast, stores, passengers, crew, but with water in boilers to steaming level.[9]

### Normal displacement

This rare term has been used to mean the ship's displacement "with all outfit, and two-thirds supply of stores, ammunition, etc., on board."[11]

## Gallery

 Nautical portal

## Notes

1. ^ Dear and Kemp, 2006, p.588
2. ^ a b Turpin and McEwen, 1980.
3. ^ a b George, 2005, p. 68.
4. ^ a b c George, 2005. p.5.
5. ^ George, 2005. p.14–15.
6. ^ George, 2005. p. 465.
7. ^ a b c George, 2005. p. 262.
8. ^ a b Department of the Navy, 1942.
9. ^ a b Military Sealift Command.
10. ^ a b United States of America, 1922. Ch II, Part 4.
11. ^ United States Naval Institute, 1897. p 809.

## References

Wikimedia Foundation. 2010.

Поможем решить контрольную работу

### Look at other dictionaries:

• Displacement — may refer to: Contents 1 Physical sciences 1.1 Physics 1.2 Engineering …   Wikipedia

• Displacement (fluid) — Two graduated cylinders containing water, one with a rock submerged in it, showing the increased water level due to displacement In fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking… …   Wikipedia

• Displacement — Dis*place ment, n. [Cf. F. d[ e]placement.] 1. The act of displacing, or the state of being displaced; a putting out of place. [1913 Webster] Unnecessary displacement of funds. A. Hamilton. [1913 Webster] The displacement of the sun by parallax.… …   The Collaborative International Dictionary of English

• displacement — ► NOUN 1) the action or process of displacing. 2) the amount by which a thing is moved from a position. 3) the volume or weight of water displaced by a floating ship, used as a measure of the ship s size. 4) Psychoanalysis the unconscious… …   English terms dictionary

• displacement — [dis plās′mənt, dis′plās′mənt] n. 1. a displacing or being displaced 2. a) the weight or volume of a fluid displaced by a floating object; specif., the weight of water, in long tons, displaced by a ship b) the volume displaced by a stroke of a… …   English World dictionary

• ship — shipless, adj. shiplessly, adv. /ship/, n., v., shipped, shipping. n. 1. a vessel, esp. a large oceangoing one propelled by sails or engines. 2. Naut. a. a sailing vessel square rigged on all of three or more masts, having jibs, staysails, and a… …   Universalium

• Ship — A ship IPA|/ʃɪp/ audio|en us ship.ogg|Audio (US) is a large vessel that floats on water. Ships are generally distinguished from boats based on size. Ships may be found on lakes, seas, and rivers and they allow for a variety of activities, such as …   Wikipedia

• Ship lifts in China — The government of China has built or is building several new ship liftsShip lifts, also called boat lifts or lift locks, are an alternative to canal locks. Unlike a canal lock a ship lift has an entire basin that the vessels enter, then water… …   Wikipedia

• ship construction — Introduction       complex of activities concerned with the design and fabrication of all marine vehicles (ship).       Ship construction today is a complicated compound of art and science. In the great days of sail, vessels were designed and… …   Universalium

• displacement — [[t]dɪsple͟ɪsmənt[/t]] 1) N UNCOUNT Displacement is the removal of something from its usual place or position by something which then occupies that place or position. [FORMAL] No barrier prevents our gradual, purposeful displacement of tradition …   English dictionary