Go to Extensive Definition

Dictionary Definition

waterline n : a line corresponding to the surface of the water when the vessel is afloat on an even keel; often painted on the hull of a ship [syn: water line, water level]

User Contributed Dictionary

see water line

English

Etymology

water + line

Noun

the line formed by the surface of the water on the hull of a ship when she is afloat; any of a series of short lines marked on the hull to show where the waterline would be under different loadings
a line showing where the water has been, usually a line separating dry land and wet areas; a watermark or tidemark
In the context of "cosmetics": the inner rim of the eyelid, just behind the lash line; primarily used in reference to the application of eyeliner

Translations

line on the hull of a ship

Finnish: vesilinja
French: ligne de flottaison
German: Wasserlinie
Russian: ватерлиния (vaterlínija)

line on the land

Finnish: vesiraja
German: Wasserstand

Extensive Definition

Waterline refers to an imaginary line marking the level at which ship or boat floats in the water. To an observer on the ship the water appears to rise or fall against the hull . Temperature also affects the level because warm water provides less buoyancy, being less dense than cold water. Likewise the salinity of the water affects the level, fresh water being less dense than salty seawater.

For vessels with displacement hulls, the hull speed is determined by, amongst other things, the waterline length. In a sailing boat, the length of the waterline can change significantly as the boat heels, and can dynamically affect the speed of the boat.

In aircraft design, the term waterline refers to the vertical location of items on the aircraft. This is the (normally) "Z" axis of an XYZ coordinate system, the other two axes being the Fuselage Station (X) and Buttock Line (Y).

Load line

The original "Plimsoll Mark" was a circle with a horizontal line through it to show the maximum draft that a ship may load to. Additional marks have been added over the years to allow for different densities of water and expected sea conditions.

Letters may also appear to the sides of the mark indicating the classification society that has surveyed the vessel's load line. The initials used include AB for the American Bureau of Shipping, LR for Lloyd's Register, GL for Germanischer Lloyd, BV for Bureau Veritas, IR for the Indian Register of Shipping and NV for Det Norske Veritas. These letters should be approximately 115 millimetres in height and 75 millimetres in width.Statutory Instruments 1998 No. 2241 The Merchant Shipping (Load Line) Regulations 1998 The Scantling length is usually referred to during and following load line calculations.

The letters on the Load line marks have the following meanings:

TF – Tropical Fresh Water
F – Fresh Water
T – Tropical Seawater
S – Summer Temperate Seawater
W – Winter Temperate Seawater
WNA – Winter North Atlantic

Fresh water is considered to have a density of 1000 kg/m³ and sea water 1025 kg/m³. Fresh water marks make allowance for the fact that the ship will float deeper in fresh water than salt water. A ship loaded to her Fresh Water mark in fresh water will float at her Summer Mark once she has passed into sea water. Similarly if loaded to her Tropical Fresh water mark she will float at her Tropical Mark once she passes in to sea water.

The Summer load line is the primary load line and it is from this mark that all other marks are derived. The position of the summer load line is calculated from the Load Line Rules and depends on many factors such as length of ship, type of ship, type and number of superstructures, amount of sheer, bow height and so on. The horizontal line through the circle of the Plimsoll mark is at the same level as the summer load line.

The Winter load line is one forty-eighth of the summer load draft below the summer load line.

The Tropical load line is one forty-eighth of the summer load draft above the summer load line. The Fresh Water load line is an amount equal to \tfrac millimetres above the summer load line where \triangle is the displacement in metric tonnes at the summer load draft and T is the metric tonnes per centimetre immersion at that draft. In any case where \triangle cannot be ascertained the fresh water load line is at the same level as the tropical load line. The position of the Tropical Fresh load line relative to the tropical load line is found in the same way as the fresh water load line is to the summer load line. The Winter North Atlantic load line is used by vessels not exceeding 100 metres in length when in certain areas of the North Atlantic Ocean during the winter period. When assigned it is 50 millimetres below the winter mark.Notes on Cargo Work: Kemp and Young: ISBN 0853090408

Timber load line marks

Certain vessels are assigned Timber Freeboards but before these can be assigned certain additional conditions have to be met. One of these conditions is that the vessel must have a forecastle of at least 0.07 the length of the vessel and of not less than standard height, which is 1.8 metres for a vessel 75 metres or less in length and 2.3 metres for a vessel 125 metres or more in length with intermediate heights for intermediate lengths. A poop or raised quarter deck is also required if the length is less than 100 metres. The letter L prefixes the load line marks to indicate a timber load line.Notes on Cargo Work: Kemp and Young: ISBN 0853090408 Except for the Timber Winter North Atlantic freeboard the other freeboards are less than the standard freeboards. This allows these ships to carry additional timber as deck cargo, but with the facility to jettison this cargo.

The letters on the Timber Load line marks have the following meanings:

LTF – Timber Tropical Fresh Water
LF – Timber Fresh Water
LT – Timber Tropical Seawater
LS – Timber Summer Seawater
LW – Timber Winter Seawater
LWNA –Timber Winter North Atlantic

The Summer Timber load line is arrived at from the appropriate tables in the Load Line Rules.

The Winter Timber load line is one thirty-sixth of the Summer Timber load draft below the Summer Timber load line.

The Tropical Timber load line is one forty-eighth of the Summer Timber load draft above the Summer timber load line.

The Timber Fresh and the Tropical Timber Fresh load lines are calculated in a similar way to the Fresh Water and Tropical Fresh water load lines except that the displacement used in the formula is that of the vessel at her Summer Timber load draft. If this cannot be ascertained then these marks will be one forty-eighth of the Timber Summer draft above the Timber Summer and Timber Tropical marks respectively.Notes on Cargo Work: Kemp and Young: ISBN 0853090408

The Timber Winter North Atlantic load line is at the same level as the Winter North Atlantic load line

Subdivision load line marks

Passenger ships which have spaces which are adapted for the accommodation of passengers and the carriage of cargo alternatively may have one or more additional load line marks corresponding to the subdivision drafts approved for the alternative conditions. These marks show C1 for the principal passenger condition, and C2, C3, etc., for the alternative conditions, however in no case shall any subdivision load line mark be placed above the deepest load line in salt water.

References

External links

waterline in Czech: Čára ponoru

waterline in German: Wasserlinie

waterline in German: Schiffsmaße

waterline in Modern Greek (1453-): Ίσαλος

waterline in Spanish: Francobordo

waterline in French: Ligne de flottaison

waterline in Hebrew: קו פלימסול

waterline in Polish: Znak wolnej burty

waterline in Russian: Ватерлиния

waterline in Finnish: Lastimerkki

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