# Ship dimensions

Under ship dimensions to different specifications, such as mass and space information, displacement, load capacity, depth, length and speed sees a ship . The following information applies to ocean-going vessels . Information on ship sizes and ship performances vary due to their different purposes and different national units of measurement .

## displacement

The term "displacement" (or displacement or Deplacement ; fr. Déplacement , engl. Displacement ) is derived from the Archimedean principle forth and illustrated that a ship is floating (or a submarine floats) when the mass of the displaced water to the mass of Ship corresponds. In terms of shipbuilding, the terms displacement and water displacement (designations: D or P ) are equated with the mass of the ship. A ship with a displacement of 10,000 tons displaces 10,000 metric tons of water. This corresponds to around 10,000 m³ of fresh water at 3.98 ° C (see old definition of the kilogram ). Since the volume-related displacement depends on the water density, ie fluctuating salinity and temperature, the draft of the ship changes. In the shipyard calculation necessary for ship measurement or, for example, when calculating loading conditions, a distinction is made between the cubic displacement (also cubic displacement), which is specified in cubic meters, and the weight displacement in metric tons or tn , due to the necessary adjustment to different water densities . l (long tons or British tons) at 1,016 kg.

Depending on the payload (e.g. cargo or fuel) and equipment, a distinction is made between construction displacement , maximum or operational displacement and (especially in the case of naval ships) standard displacement .

In German naval history, the design displacement was decisive for warships for a long time. This mass was calculated from the empty ship, the crew, the full supply of ammunition, drinking and washing water, provisions and other consumables as well as half the supply of boiler feed water, lubricating oil and fuel.

As part of the Washington Naval Agreement in 1922 was for warships , the standard displacement introduced. It was considered a binding official information for the signatory states in order to have a uniform comparison value, and was adopted by many other navies over time. The standard displacement (with the unit  ts ) characterizes the water displacement of the operational warship minus the fuel and boiler feed water supplies.

For merchant ships that are supposed to carry as much cargo as possible, an indication of the size based on the water displacement does not make much sense, since the state of loading often changes and the total mass is therefore not an economically relevant figure.

Instead, the carrying capacity is important for merchant ships. This is referred to with the English terms deadweight tonnage (dwt) or tons deadweight ( tdw ). The indication tons deadweight all told ( tdwat , also TDWAT, T dwat or simply tdw) denotes the total carrying capacity of a merchant ship. This measure is calculated from the difference between the water displacement of the ship loaded up to the maximum permissible loading mark and that of the unloaded ship. Units of measurement are optionally metric tons of 1000 kg each or English long tons ( tn. L. ) Of 1016 kg.

### TEU

In the case of container ships , the loading or storage capacity is given in the number of containers. The unit of measurement is the TEU ( twenty-foot equivalent unit ). This means a standard container 20 feet long. A container ship with 6,000 TEU offers space for 6,000 20-foot containers, with an optimal distribution of the weights of the individual containers and taking into account the line of sight . In order to give a more precise picture of the load capacity, experts also use the 14mt homogeneous load . This value indicates how many containers, each weighing 14 metric tons, a ship can load. The actual capacity can, however, vary considerably depending on the route, mostly downwards.

In the Middle Ages, the carrying capacity was given in loads or loads , which roughly corresponded to the carrying capacity of a single wagon.

## Volume, tonnage

### history

The determination of ship sizes became necessary when one began to burden ships with taxes in order to cover costs for ports , beacons or the dredging of fairways .

The term barrel originated at a time when ships were measured by the number of "tons", or barrels, that they could carry. Different port cities used different dimensions, so that the specification of the reference dimension, e.g. B. the "Lübschen bin" defined by Lübeck was necessary. At the same time, load-bearing capacity information was also used in "Loads".

In Great Britain, tons were used according to Builder's Measurement until around 1870 , calculated according to the formula:

${\ displaystyle \ mathrm {tons ~ (bm)} = {\ frac {\ left (L - {\ frac {3B} {5}} \ right) \ cdot B \ cdot {\ frac {B} {2}} } {94}}}$

where L… length in feet, B… width in feet.

The register bin is an obsolete measure of space (since 1969 in Germany, later in Austria) , so no indication of mass . One register ton corresponds to 100 English cubic feet or 2.832 m³.

A distinction was gross tons , short BRT (Engl. GRT Gross Registered Tons ) of net registered tons or NRT (Engl. Net Registered Tons ).

BRT covered the whole ship, so

• between surveying and upper deck,
• below the measurement deck (lower deck space content),
• Content of hatches above deck,
• Content of the superstructures.

NRT are calculated from BRT through deductions, namely the

• Crew accommodation,
• Fuel bunker,
• Command bridge,
• Machine and boiler rooms,
• Pump rooms,
• Provision rooms,
• Water ballast tanks,
• Workshops and storerooms.

In some cases, these rooms were not included in the calculation according to the actual volume, but with considerably higher values ​​in accordance with certain exception rules, which therefore also manifested themselves in certain structural features of the ships concerned.

Port fees, canal passage fees or pilotage fees are calculated according to the NRT.

### Gross and net tonnage (GT, NRZ)

The dimensionless numbers gross tonnage (GT), English: Gross-Tonnage (GT), and net tonnage (NRZ) designate the size of a ship today. According to the GT or NRZ, the tonnage dues , the fees for port use (port fees), canal or lock passage and pilotage are still calculated . GT and NRZ replace the obsolete gross register ton (BRT) and net register ton (NRT).

The exact calculation of the GT is carried out using the following formulas:

${\ displaystyle BRZ = K_ {1} \ cdot V}$
${\ displaystyle K_ {1} = 0 {,} 2 + 0 {,} 02 \ cdot \ log _ {10} V}$

V is the numerical value of the content of all enclosed spaces, measured in cubic meters, from the keel to the chimney. K 1 is a value which lies between 0.22 and 0.32 and is dependent on the size of the ship (i.e. V between 10 and 1 million m³). If a ship has a volume of 10,000 m³, this results in K 1 = 0.28 and thus a GT of 2,800.

The NRZ depends on the contents of the holds, the draft, the side height and the number of passengers. The NRZ calculated using a special formula must not be less than 30% of the GT. Open container ships and double-hull tankers receive a reduction in GT in accordance with the relevant IMO regulations. This is noted in the ship's measurement certificate.

These values ​​are recorded in the official international ship measurement certificate ( International Tonnage Certificate ), which is issued by the Federal Maritime and Hydrographic Agency (BSH) when a ship is put into service in Germany . In Austria, depending on the size of the ship, the federal states or (from 24 m) the highest federal shipping authority are responsible for this.

The EU sets a factor of 0.24 for yachts . Austrian yachts in particular were at a disadvantage before the introduction of the GT, as the measurement according to the BRT could result in around twice the canal fee as for the same yacht under the German flag. The tonnage registered in the German flag certificates had come about through a different formula. No international ship's measurement certificate is required for yachts less than 24 meters in length.

## Draft

Ahming at the bow of a modern freighter
Ahming at the stern of the Gorch Fock

The draft of a ship is defined as the distance from the surface of the water to the deepest point of the ship (usually the lower edge of the keel) when the water is in a stable, unmoving position in calm water. It must be observed especially in shallow waters and decides e.g. B. about which ports the ship can enter. The draft increases when the ship dips deeper into the water as a result of a higher load, and is also influenced by the density of the water, which changes as a result of different salinity and different temperatures. Basically, a ship plunges deeper into fresh water than into salt water. Apart from these static influences on the draft, the dynamic influence of the up and down movements in the sea and in motion must also be taken into account.

The draft and the trim also result in the above water level of the ship, which is necessary to know, for example, to maintain bridge clearance heights .

### Ahming

Ahmings are draft marks that are affixed to the bow and stern of a seagoing ship and sometimes also amidships. The draft is calculated from the lower edge of the keel up and given in decimeters or English feet. Sometimes both figures are found in parallel (information in decimeters on one side, information in English feet on the other side of the ship).

### Side height

The side height is the vertical distance, measured from the lower edge of the keel to the upper edge of the freeboard deck beam ( deck line ) on the board side. With so-called effective superstructures, the side height can also be greater than the height of the freeboard deck. This is particularly the case with ferries.

### Freeboard

Freeboard is the distance, measured vertically downwards amidships, from the freeboard deck (marked on the hull by the upper edge of the deck line ) to the upper edge of the freeboard mark or the corresponding loading mark or the actual waterline .

When the ship is submerged, the freeboard is reduced by loading in favor of the draft.

The current freeboard can be checked from the outside at any time using the markings on the hull of the ship. The specified minimum freeboard to be observed ensures sufficient buoyancy to keep the ship stable in any sea state.

### Freeboard mark

From left to right: loading mark, freeboard mark of the classification society Bureau Veritas and Ahming

The freeboard mark (also Plimsoll mark after Samuel Plimsoll , who introduced it in the 1870s) indicates the limit for the freeboard of the ship's hull, which can be changed as a result of loading. In the case of merchant ships, it is located halfway along the length of the ship near the main frame bulkhead on both sides of the hull of the ship, exactly below the deck line that marks the position of the freeboard deck .

The freeboard mark consists of a ring of 300 millimeters (12  inches ) outside diameter and 25 millimeters (1 inch) wide, which is cut by a horizontal line 450 millimeters (18 inches) long and also 25 millimeters (1 inch) wide; the top of the line runs through the center of the ring.

This mark should be marked so permanently - for example by welding on steel - that it remains recognizable even if the paint flakes off.

The distance of the freeboard mark from the deck line (upper edge of the line to the upper edge of the line) corresponds to the summer freeboard for seagoing vessels in salt water.

The letters on the ring of the freeboard mark indicate the classification society (115 mm font size):

Note: Symmetrical symbols similar to the Plimsoll symbol ⦵ are also used in physics and chemistry to indicate a standard state and on camera housings to mark the position of the image plane (film plane).

In addition to the freeboard mark (line with circle), loading marks of different heights indicate the permitted immersion depths in water of different densities.

From a vertical line 540 millimeters (21 inches) in front of the center of the ring of the freeboard mark 25 mm (1 inch) wide, several equally wide horizontal lines 230 mm (9 inches) long start.

The top two levels for fresh water of the inland waters to the rear, i.e. towards the circle mark, four lower levels for the denser salt water of the seas to the front, i.e. away from the freeboard mark. This avoids the brands for cold fresh water and tropical warm salt water being too close together and achieves a memorable design. The upper edges of the lines apply as the marked height. Slightly above or to the side of the free end of the line, these loading marks are marked as follows:

• TF = freeboard fresh water tropics ("F" for fresh water)
• F = freeboard in fresh water
• T = freeboard in tropical sea water (salt water of the sea)
• S = summer loading mark in sea water (identical to the freeboard mark in a circle according to the freeboard certificate)
• W = freeboard in sea water in winter
• WNA = Freeboard in sea water in winter in the North Atlantic

The relative position of the loading label ladder to the right or left of the Plimsoll circular label always points to the bow and thus also makes it clear which side of the ship you are facing: starboard or port.

### Wooden freeboard

Plimsoll mark with wooden freeboard

If wooden freeboards (special freeboard for the transport of wood on deck) are issued upon request, these are marked in addition to the loading marks. These timber loading tags are designed like the regular loading tags, except that they are placed 540 millimeters (21 inches) behind the center of the ring of the freeboard tag.

• LTF = wood-tropical-fresh water (F for fresh water)
• LF = wood fresh water
• LT = wood tropics
• LS = wood summer
• LW = wood winter
• LWNA = Wood-Winter-North Atlantic

The preceding "L" probably comes from Engl. lumber for lumber to lumber. The “L” marks are higher, so a ship may be heavily loaded with wood under certain circumstances, if care is taken that part of the cargo can be dropped at sea in an emergency in order to relieve the ship somewhat.

### Fresh water brand

On sailing ships, in addition to the freeboard mark, only fresh water (* F) and winter North Atlantic loading marks (* WNA) are marketed.

### Sink mark (barge)

Inland vessel sink mark

• Passenger ships and floating devices must have sink marks on both sides around midships. Freight ships over 40 meters in length must also bear such marks on both sides at a distance of about one sixth of the length from the bow and stern; for ships under 40 meters in length, two sink marks are sufficient on each side.
• The depression marks must have a length of 30 cm and a height of 4 cm. They are ineradicably light on a dark background or dark on a light background so that their lower edge corresponds to the deepest depression.

While the lower edge of the line is the limit at this indentation mark, the upper edge of the upper edge applies to the loading mark lines across and next to the Plimsoll ring.

## Length specifications

Ribs and waterline cracks (bow is on the right)

The lengths of a ship are usually given in Germany as:

Abbr. engl. meaning specification
LaD Length on deck from the foremost to the rearmost fixed point (leading edge of the stem - trailing edge of the stern stem at deck height)
Lua Loa Length over all from the foremost to the rearmost fixed point (bow - stern); for sailing ships, if not excluded, from jib boom - stern / besannock
LzdL Lpp
out of date Lbp
Length between perpendiculars Intersection of the waterline stem on KWL (VL) - middle of the rudder stock (HL). Length between the perpendiculars
Fiber optic Length in the swimming water line (KWL; leading edge of stem - trailing edge of stern post in KWL including rudder blade)
VL FP Front plumb Cut of the Vorsteven with the KWL
HL AP Back plumb mostly rudder axis
KWL Construction waterline Swimming waterline at summer freeboard
Büa boa Width over everything measured in the middle of the ship or at the widest point
B. Construction width measured on the outer edge of the frame on steel ships
R. Room depth Internal dimensions of the ship, upper edge of the floor walls - lower edge of the uppermost continuous deck, measured amidships at half the length of the ship
Day Greatest draft
T Construction depth measured on the lower edge of the floor wall on steel ships halfway between the perpendiculars (Lpp)
H Side height Height of the hull from the upper edge of the beam keel to the deck, measured laterally at half the length of the ship
F. Freeboard measured from KWL to the upper edge of the decking on the side of the ship at half the ship's length
V Displacement of the ship on frames

Note: With wooden ships, unlike steel ships, all dimensions are measured on the outer edge of the planking; L, T to the point where the outer skin runs into the stern or keel (sponation).

## Height information

In addition to the side height, the total height of ships is also given. A distinction is made here:

• Height above the lower edge of the keel to the upper edge of the superstructure or chimney or top of the mast
• Height above construction waterline (KWL) to the upper edge of the superstructure or chimney or top of the mast (results from the above by subtracting the draft)
• for sailing ships also: mast height above deck
• Fixed point height between the water level and the highest fixed point of a ship. It is decisive for whether a ship can pass a bridge or other overhead obstacle.

## Shape coefficients

Characteristic values ​​can be derived from the main dimensions. They allow an initial rough assessment of the properties of the ship or boat. This also only applies to conventional forms, for example not to planing boats. For detailed considerations on a specific watercraft, the three-dimensional flow condition is too complex to be reduced to a few numbers.

The maximum for these coefficients is 1; this applies to a cuboid . Theoretically, the minimum is 0. The most important coefficients are shown below.

### Block coefficient

The block coefficient C B indicates the ratio between the displaced volume of the ship and the block   L pp  ×  B   ×  T   : ${\ displaystyle \ nabla}$

${\ displaystyle C_ {B} = {\ frac {\ nabla} {L_ {pp} \ cdot B \ cdot T}}}$

The smaller C B , the “slimmer” the ship. High-speed vessels usually have a small C B . The block coefficient is as solidity referred.

### Waterline coefficient

The waterline coefficient C WP indicates the ratio of the area of ​​the construction waterline A W to the rectangle   L pp  ×  B  :

${\ displaystyle C_ {WP} = {\ frac {A_ {W}} {L_ {pp} \ cdot B}}}$

A large waterline coefficient in combination with a small block coefficient means great stability, both across and fore and aft.

### Midship coefficient or main bulkhead coefficient

The main frame coefficient C M indicates the ratio of the main frame area A M to the rectangle   B   ×  T   :

${\ displaystyle C_ {M} = {\ frac {A_ {M}} {B \ cdot T}}}$

A main frame coefficient close to 1 suggests a very complete ship, a fast boat would have a lower value here. If the frame shape becomes triangular, the result is 0.5.

If the frame with the largest area is not exactly half the length (L pp ) (as in a conventional merchant ship), the largest frame area A X can be used instead of this main frame and its area A M.

### Prismatic coefficient

The prismatic coefficient (of length), also called the degree of sharpness , C P indicates the ratio between the volume V of the submerged part of the ship and the block   A M  ×  L pp   :

${\ displaystyle C_ {P} = {\ frac {V} {L_ {pp} \ cdot A_ {M}}} = {\ frac {L_ {pp} \ cdot B \ cdot T \ cdot C_ {B}} { L_ {pp} \ cdot (B \ cdot T \ cdot C_ {M})}} = {\ frac {C_ {B}} {C_ {M}}}}$

C P strongly influences the displacement resistance of the ship and thus the required propulsion power (the smaller C P , the lower the force required at constant speed).

Alternatively, A X can be used again for unusual shapes (e.g. yacht) .

## Speed ​​information

The speed of seagoing vessels is given in knots , on inland waterways one takes km / h . One knot (kn) corresponds to one nautical mile per hour , i.e. 1.852 km / h. A distinction is made between the speed of travel relative to the water and the true speed influenced by the current and wind , the speed over the ground .

The so-called Froude number is characteristic of the speed of a ship . It is defined as

${\ displaystyle F_ {n} = {\ frac {v} {\ sqrt {g \ cdot L_ {WL}}}}}$

with: L WL length in the water line, g acceleration due to gravity , v speed relative to the water

A certain Froude area can be assigned to each type of ship, in which it can sail economically, for example:

• Container freighters 0.15-0.25
• Tug 0.25-0.30
• Gliding vehicles> 0.50

With the Froude number, the characteristics of the propagation of the bow and stern waves and the drag induced thereby change.

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