Waterline
Encyclopedia
The term "waterline" generally refers to the line where the hull of a ship
meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft
of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures. Temperature affects the level because warm water provides less buoyancy
, being less dense than cold water. The salinity
of the water also affects the level, fresh water being less dense than salty seawater
. This marking was invented in the 1870s by Samuel Plimsoll
.
For vessels with displacement hulls, the hull speed
is determined by, amongst other things, the waterline length
. In a sailing
boat, the waterline length 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).
The purpose of a 'load line' is to ensure that a ship has sufficient freeboard
(the height from the water line to the main deck) and thus sufficient reserve buoyancy
(e.g., the enclosed volume created by the area between the waterline and the main deck). The freeboard of commercial vessels is measured between the lowest point of the uppermost continuous deck at side and the waterline and this must not be less than the freeboard marked on the Load Line Certificate issued to that ship. All commercial ships, other than in exceptional circumstances,Statutory Instruments 1998 No. 2241 The Merchant Shipping (Load Line) Regulations 1998 Sections 5(1) and 5(3) have a load line symbol painted amidships on each side of the ship. This symbol must also be permanently marked, so that if the paint wears off it remains visible. The load line makes it easy for anyone to determine if a ship has been overloaded. The exact location of the Load Line is calculated and/or verified by a Classification Society
and that society issues the relevant certificates.
This symbol, also called an international load line or Plimsoll line, indicates the maximum safe draft
, and therefore the minimum freeboard for the vessel in various operating conditions.Notes on Cargo Work: Kemp and Young: ISBN 0853090408
The plimsoll mark is also used in chemistry as a symbol to denote a standard state
.
In the Middle Ages the Venetian Republic, the city of Genoa and the Hanseatic league required ships to show to a load line. In the case of Venice this was a cross marked on the side of the ship and of Genoa three horizontal lines.
The first 19th century loading recommendations were introduced by Lloyd's Register of British and Foreign Shipping
in 1835, following discussions between shipowners, shippers and underwriters. Lloyds recommended freeboards as a function of the depth of the hold (three inches per foot of depth). These recommendations, used extensively until 1880, became known as "Lloyd's Rule".
In the 1860s, after increased loss of ships due to overloading, a British MP, Samuel Plimsoll
, took up the load line cause. A Royal Commission on unseaworthy ships was established in 1872, and in 1876 the United Kingdom Merchant Shipping Act made the load line mark compulsory, although the positioning of the mark was not fixed by law until 1894. In 1906, laws were passed requiring foreign ships visiting British ports to be marked with a load line. It was not until 1930 (The 1930 Load Line Convention) that there was international agreement for universal application of load line regulations.
In 1966 a Load Lines Convention was held in London which re-examined and amended the 1930 rules. The 1966 Convention has since seen amendments in 1971, 1975, 1979, 1983, 1995 and 2003.
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
, RI for the Registro Italiano Navale
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 Load Line Length is referred to during and following load line calculations.
The letters on the Load line marks have the following meanings:
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
centimetres above the summer load line where 
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
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
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:
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
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft
Draft (hull)
The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...
of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures. Temperature affects the level because warm water provides less buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
, being less dense than cold water. The salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
of the water also affects the level, fresh water being less dense than salty seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
. This marking was invented in the 1870s by Samuel Plimsoll
Samuel Plimsoll
Samuel Plimsoll was a British politician and social reformer, now best remembered for having devised the Plimsoll line .-Early life:Plimsoll was born in Bristol and soon moved to Whiteley Wood...
.
For vessels with displacement hulls, the hull speed
Hull speed
Hull speed, sometimes referred to as displacement speed, is the speed of a boat at which the bow and stern waves interfere constructively, creating relatively large waves, and thus a relatively large value of wave drag...
is determined by, amongst other things, the waterline length
Waterline length
The Waterline length is a measurement of ships and boats. The term denotes the length of the vessel at the point where it sits in the water. It excludes the total length of the boat, such as features that are out of the water...
. In a sailing
Sailing
Sailing is the propulsion of a vehicle and the control of its movement with large foils called sails. By changing the rigging, rudder, and sometimes the keel or centre board, a sailor manages the force of the wind on the sails in order to move the boat relative to its surrounding medium and...
boat, the waterline length 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).
The purpose of a 'load line' is to ensure that a ship has sufficient freeboard
Freeboard (nautical)
In sailing and boating, freeboardmeans the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship...
(the height from the water line to the main deck) and thus sufficient reserve buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
(e.g., the enclosed volume created by the area between the waterline and the main deck). The freeboard of commercial vessels is measured between the lowest point of the uppermost continuous deck at side and the waterline and this must not be less than the freeboard marked on the Load Line Certificate issued to that ship. All commercial ships, other than in exceptional circumstances,Statutory Instruments 1998 No. 2241 The Merchant Shipping (Load Line) Regulations 1998 Sections 5(1) and 5(3) have a load line symbol painted amidships on each side of the ship. This symbol must also be permanently marked, so that if the paint wears off it remains visible. The load line makes it easy for anyone to determine if a ship has been overloaded. The exact location of the Load Line is calculated and/or verified by a Classification Society
Classification society
A classification society is a non-governmental organization that establishes and maintains technical standards for the construction and operation of ships and offshore structures...
and that society issues the relevant certificates.
This symbol, also called an international load line or Plimsoll line, indicates the maximum safe draft
Draft (hull)
The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...
, and therefore the minimum freeboard for the vessel in various operating conditions.Notes on Cargo Work: Kemp and Young: ISBN 0853090408
The plimsoll mark is also used in chemistry as a symbol to denote a standard state
Standard state
In chemistry, the standard state of a material is a reference point used to calculate its properties under different conditions. In principle, the choice of standard state is arbitrary, although the International Union of Pure and Applied Chemistry recommends a conventional set of standard states...
.
History
The first official loading regulations are thought to date back to maritime legislation originating with the kingdom of Crete in 2,500 BC when vessels were required to pass loading and maintenance inspections. Roman sea regulations also contained similar regulations.In the Middle Ages the Venetian Republic, the city of Genoa and the Hanseatic league required ships to show to a load line. In the case of Venice this was a cross marked on the side of the ship and of Genoa three horizontal lines.
The first 19th century loading recommendations were introduced by Lloyd's Register of British and Foreign Shipping
Lloyd's Register
The Lloyd's Register Group is a maritime classification society and independent risk management organisation providing risk assessment and mitigation services and management systems certification. Historically, as Lloyd's Register of Shipping, it was a specifically maritime organisation...
in 1835, following discussions between shipowners, shippers and underwriters. Lloyds recommended freeboards as a function of the depth of the hold (three inches per foot of depth). These recommendations, used extensively until 1880, became known as "Lloyd's Rule".
In the 1860s, after increased loss of ships due to overloading, a British MP, Samuel Plimsoll
Samuel Plimsoll
Samuel Plimsoll was a British politician and social reformer, now best remembered for having devised the Plimsoll line .-Early life:Plimsoll was born in Bristol and soon moved to Whiteley Wood...
, took up the load line cause. A Royal Commission on unseaworthy ships was established in 1872, and in 1876 the United Kingdom Merchant Shipping Act made the load line mark compulsory, although the positioning of the mark was not fixed by law until 1894. In 1906, laws were passed requiring foreign ships visiting British ports to be marked with a load line. It was not until 1930 (The 1930 Load Line Convention) that there was international agreement for universal application of load line regulations.
In 1966 a Load Lines Convention was held in London which re-examined and amended the 1930 rules. The 1966 Convention has since seen amendments in 1971, 1975, 1979, 1983, 1995 and 2003.
Standard load line marks
The original "Plimsoll Mark" was a circle with a horizontal line through it to show the maximum draft of a ship. Additional marks have been added over the years, allowing for different water densities and expected sea conditions.Letters may also appear to the sides of the mark indicating the classification society
Classification society
A classification society is a non-governmental organization that establishes and maintains technical standards for the construction and operation of ships and offshore structures...
that has surveyed the vessel's load line. The initials used include AB for the American Bureau of Shipping
American Bureau of Shipping
The American Bureau of Shipping is a classification society, with a mission to promote the security of life, property and the natural environment, primarily through the development and verification of standards for the design, construction and operational maintenance of marine-related facilities...
, LR for Lloyd's Register
Lloyd's Register
The Lloyd's Register Group is a maritime classification society and independent risk management organisation providing risk assessment and mitigation services and management systems certification. Historically, as Lloyd's Register of Shipping, it was a specifically maritime organisation...
, GL for Germanischer Lloyd
Germanischer Lloyd
The Germanischer Lloyd SE is a classification society based in the city of Hamburg, Germany. As a technical supervisory organization Germanischer Lloyd conducts safety surveys on more than 7,000 ships with over 100 Mio GT...
, BV for Bureau Veritas
Bureau Veritas
Bureau Veritas S.A. is a multinational company providing conformity assessment, certification and consulting services to industry, government and individuals. Originally formed in Antwerp in 1828 as Bureau de Renseignements pour les Assurances Maritimes , the Bureau Veritas name was adopted in 1829...
, IR for the Indian Register of Shipping
Indian Register of Shipping
Indian Register of Shipping is an internationally recognized independent ship classification society, founded in India in 1975. It is a member of the International Association of Classification Societies ....
, RI for the Registro Italiano Navale
Registro Italiano Navale
"For over 140 years at the service of the shipping and industrial world."RINA was founded in Genoa in 1861 under the name REGISTRO ITALIANO NAVALE, by the "Associazione della Mutua Assicurazione Marittima" [established in Genoa in 1857 by ship managers and shipowners , to cover risks related to...
and NV for Det Norske Veritas
Det Norske Veritas
Stiftelsen Det Norske Veritas is a classification society organized as a foundation, with the objective of "Safeguarding life, property, and the environment". The organization's history goes back to 1864, when the foundation was established in Norway to inspect and evaluate the technical condition...
. 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 Load Line Length is 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
centimetres above the summer load line where 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
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
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
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 forecastleForecastle
Forecastle refers to the upper deck of a sailing ship forward of the foremast, or the forward part of a ship with the sailors' living quarters...
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 having 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.See also
- Ballast tankBallast tankA ballast tank is a compartment within a boat, ship or other floating structure that holds water.-History:The basic concept behind the ballast tank can be seen in many forms of aquatic life, such as the blowfish or argonaut octopus, and the concept has been invented and reinvented many times by...
- Classification SocietyClassification societyA classification society is a non-governmental organization that establishes and maintains technical standards for the construction and operation of ships and offshore structures...
- Coffin shipCoffin shipCoffin ship is the name given to any boat that has been overinsured and is therefore worth more to its owners sunk than afloat. These were hazardous places to work in the days before effective maritime safety regulation. They were generally eliminated in the 1870s with the success of reforms...
- Hull (watercraft)Hull (watercraft)A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
for general definitions. - Plimsoll shoePlimsoll shoeA plimsoll shoe, plimsoll, or plimsole is a British English word for a type of athletic shoe with a canvas upper and rubber sole, developed as beachwear in the 1830s by the Liverpool Rubber Company. The shoe was originally, and often still is in parts of the United Kingdom, called a 'sand shoe' and...
- Sailing ballastSailing ballastBallast is used in sailboats to provide moment to resist the lateral forces on the sail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. If a sailing vessel should need to voyage without cargo then ballast of...
- SS London (1864)SS London (1864)The SS London was a British steamship which sank in the Bay of Biscay on 11 January 1866. The ship was travelling from Gravesend in England to Melbourne, Australia when she began taking in water on 10 January...
- sank in 1866 and stimulated Parliament to introduce the Plimsoll line - Stability conditions (watercraft)Stability conditions (watercraft)Stability conditions is the term used to describe the various standard loading configurations to which a ship, boat, or offshore platform may be subjected. They are recognized by classification societies such as Lloyd's Register, American Bureau of Shipping and Det Norske Veritas...
- The Onedin Line (episode-Danger level)
- Waterline lengthWaterline lengthThe Waterline length is a measurement of ships and boats. The term denotes the length of the vessel at the point where it sits in the water. It excludes the total length of the boat, such as features that are out of the water...