Historical background leading to the adoption of the Load Lines convention

The stability of ships can be seriously affected by overloading, especially if the cargo shifts during the course of the voyage and the practice of marking ships to indicate how low they may safely rest in the water when loaded goes back several centuries. Most merchant ships today are covered by the International Convention on Load Lines, 1966, as amended.

The Load Lines Convention contains detailed regulations on the assignment of the freeboard (the vertical distance between the top of the hull and the waterline) and the specific limitations to which different types of ships may be loaded. Several lines are painted on the ship, above and below the central freeboard line - because ships may be loaded to a greater or lesser degree depending on the zone and season, as potential hazards vary.

Load lines - history
Lloyd's Rule
Plimsoll line
First International load lines regulations
1930 Load Line Convention
1966 Load Lines Convention
Considerations for calculating a ship's freeboard

Load lines - history
The first seafarers who set to sea in wooden canoes thousands of years ago must have already - perhaps by trial and error - worked out the optimum freeboard for these vessels. Some too, probably discovered that overloading the vessel could have severe consequences.

The first official loading regulations are thought to date back to maritime legislation originating with the island 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 - which controlled much of the sea trade in the Mediterranean - had laws requiring vessels to be loaded to a maximum depth indicated by a fixed line marked on the side of the hull. Ships from Venice were marked with a cross, while the city of Genoa used three horizontal bars.

Elsewhere, the Hanseatic League, which controlled much of the trade from the Rhine to the eastern and northern Baltic up to the seventeenth century, issued a law in 1288 from the Scandinavian town of Visby, its commercial centre, which required ships to load to a load line or face penalties.

Later, under standard maritime procedures developed for Baltic Sea at a meeting in Copenhagen in 1561, a captain could be fined "for overburdening his ship".
By the seventeenth century, ships were trading on longer voyages to the Far East, India and the Americas and each emerging maritime nation drew up its own maritime regulations. However, specific load line regulations were not passed until the nineteenth century, which saw a huge increase in seagoing trade in raw materials and finished goods as the Industrial Revolution got under way.

But as trade grew, so did the number of ships being lost. Moreover, changing technology -with sails turning to steam and wood being replaced by steel - meant experience in ship design could not always keep pace and sometimes ships were designed with inadequate freeboards.

Lloyd's Rule
The first 19th century loading recommendations were introduced by London-based Lloyd's Register of British and Foreign Shipping in 1835, following discussions between shipowners, shippers and underwriters.

Lloyd's Register recommended freeboards as a function of the depth of the hold (three inches per foot of depth) and these recommendations, used extensively until 1880, became known as "Lloyd's Rule".

However, the Rule only applied to ships registered with Lloyd's.

Concern in the United Kingdom about the growing number of ship losses led to the appointment of a Royal committee which in 1836 cited bad design and improper building - but not overloading - as contributory factors to the unseaworthiness of ships.

However, the United Kingdom Government passed a law in 1850 setting up the Marine Department of the board of Trade, to enforce application of laws governing manning, crew competence and operation of merchant vessels.

Nonetheless, seafarers themselves had little say in the safety standards aboard what one captain described as a "coffin ship". In fact, until 1871, it was actually illegal for seafarers to refuse to go to sea, even on the grounds that the ship they were sailing on was unseaworthy. In 1866 four successive crews refused to serve on a ship called the Harkaway on the understandable grounds that even at anchor in a calm sea the ship took on more than one metre of water a day. They were sent to prison.

Plimsoll line
In the 1860s, calls for regulations to limit overloading on ships were growing in the United Kingdom.

A shipowner from northern England, James Hall, was concerned about the impact on insurance rates of the high number of shipping casualties - losses had doubled in 30 years. Although many shipowners were portrayed as irresponsible, Hall could see the benefits - in terms of lower insurance rates - of getting all shipowners to abide by good practices.

In particular, Hall petitioned the Board of Trade to investigate the large number of ship losses and the Board of Trade inquiry found overloading was one of the factors to blame.

Meanwhile, a coal dealer and liberal Member of Parliament, Samuel Plimsoll, took up the load line cause. Plimsoll began a battle to try and get merchant shipping laws reformed - against stiff opposition from a minority of shipowners.

A Royal commission on Unseaworthy Ships was set up in 1872 and finally the United Kingdom Merchant Shipping Act of 1876 made load lines compulsory. The load line mark included in the legislation - though the position of the line was not fixed by law until 1894 - became known as the "Plimsoll Line": a circle with a horizontal line through the middle.

Figures on ship casualties probably helped to goad the British parliamentarians into action: in the year 1873 4, around the coastline of the United Kingdom, 411 ships sank, with the loss of 506 lives. But this figure only covers the United Kingdom coastline: between 1867 and 1882, loss of life in British vessels alone (and excluding fishing vessels) totalled 33,427 seafarers and 5,987 passengers. Ships lost numbered 16,393.

In 1906, laws were passed requiring foreign ships visiting British ports to be marked with a load line, while a German law of 1903 also issued freeboard regulations, spreading the regulatory net further.

In the United States, American vessels were loaded to a formula based on "inches per foot of depth of hold" until 1917 when the U.S. Shipping Board required adherence to British Board of Trade standards based on a set of calculated freeboard tables.

Load line legislation was introduced in the American congress in 1920 and failed, but a Load Line Act was passed in the United States in 1929.

By that time, there was a proliferation of different freeboard rules in use by various marine administrations and classification societies, which meant there was a lack of global standardization.


First International load lines regulations
The first international conference on load line regulations was envisaged for 1913, but the approaching war meant this planned conference was never held.
In 1922, however, the British Chamber of Shipping sponsored a conference, which adopted recommendations derived from studies on existing regulations elsewhere, with a view to eventually adopting them as international regulations.

Further preparatory work by the major maritime nations of the time resulted in an international conference held in London in 1930 - which adopted the first International Load Line Convention.

The rules adopted at the conference were not based on exact scientific principles - but were essentially a compromise between the various national rules which had been developed previously.

1930 Load Line Convention
The 1930 Load Line Convention was the first international agreement for universal application of load line regulations and applied to seagoing ships in international trade and was based on the principle of reserve buoyancy, although it was recognized then that the freeboard should also ensure adequate stability and avoid excessive stress on the ship's hull as a result of overloading.

The rules covered superstructure evaluations, freeboards and strength standards.

The minimum freeboard was designed to provide a standard of "reserve buoyancy" (the volume of the watertight hull above the load waterline), while the protection of openings in the hull and superstructures, such as hatches, ventilators, airpipes, scuppers, overhead discharges and the access openings in the end bulkhead of superstructures were an important consideration in the assignment of freeboard.

Another major concern was the protection for the crew by consideration of the strength of gangways, guard rails, lifelines and the height of the working platform itself.

The calculated freeboard was the basic minimum summer freeboard in salt water. The regulations divided the world into different geographical/seasonal zones, with different load lines for each - in recognition of the fact that sea and weather conditions vary greatly in different sea areas and in different seasons of the year. A ship sailing in winter in the North Atlantic Ocean had to have an increase in freeboard while for voyages in the tropical zones and in fresh water there was a freeboard deduction.

Freeboard was measured from the top of the deck amidships to the top of the line through the centre of the load line disc. Forward of the disc was a grid composed of lines indicating the maximum loading, for the summer a the level with the line in the disc and others further down for winter, for winter in the north Atlantic and above for the tropical zones and for fresh water.

Special rules were provided for tankers and for the carriage of timber deck cargo.

The 1930 load Line Convention was an important step in establishing universally applicable rules.

However, the decades following the adoption of the 1930 Convention saw developments in ship design and methods of construction which began to make the Convention rules look outdated: ships, especially tankers, grew considerably in size; specialized ship designs to meet different trades were becoming prevalent; machinery spaces in dry cargo ships were being located away from the traditional midships position; metal hatchway covers were replacing wooden ones; and welding was replacing riveting.

There was general agreement that the 1930 Convention needed revision, in particular in the sections concerning aspects relating to ship design and construction.
As a result, maritime nations planned a conference to adopt a revised Convention.

In the meantime, the International Maritime Organization had come into being and was clearly the right Organization to host the proposed conference.

1966 Load Lines Convention
The 1966 International Conference on Load Lines was held at IMO headquarters in London from 3 March to 5 April 1966 and was attended by delegations from 52 States and observers from 8 States. The International Convention on Load Lines, 1966, was adopted on 5 April 1966 and entered into force on 21 July 1968. The terms of the convention stated it would enter into force 12 months after at least 15 countries, seven of which possessed not less than one million gross tons of shipping had accepted it. These conditions were met in a remarkably short time - one reason being that the Convention provided for a general reduction in freeboard allowance for most ships compared to the 1930 Convention.

Work of the 1966 Conference
The 1966 conference agreed that the revision of the 1930 Load Line convention required re-examination of a number of issues, including: prevention of the entry of water into the hull; adequate reserve buoyancy; protection of the crew; adequate structural strength of the hull; and limitation of water on the deck.

Like the 1930 Convention, the 1966 Load Lines Convention sets out rules for calculation and assignment of freeboard and takes into account the potential hazards present in different zones and different seasons. The technical annex contains several additional safety measures concerning doors, freeing ports, hatchways and other items. The main purpose of these measures is to ensure the watertight integrity of ships' hulls below the freeboard deck.

All assigned load lines must be marked amidships on each side of the ship, together with the deck line. Ships intended for the carriage of timber deck cargo are assigned a smaller freeboard as the deck cargo provides protection against the impact of waves.

The 1966 Convention is made up of:

  • Articles - cover matters of contract between governments, survey and certification.
  • Annex I - Regulations for determining load lines, is divided into four chapters.
  • Chapter I - General -for example, strength of hull, types of ships, definitions, markings.
  • Chapter II - Conditions of assignment of freeboard;
  • Chapter III - Freeboards - evaluation of freeboard in terms of geometrical and physical characteristics of any ship.
  • Chapter IV - Special requirements for ships assigned timer freeboards.
  • Annex II defines zones, areas and seasonal periods appropriate to the various load line markings.
  • Annex III prescribes the form and scope of certificates, including the International Load Line Certificate and the International Load Line Exemption Certificate .

The 1966 Convention has since been amended, see International Convention on Load Lines


Considerations for calculating a ship's freeboard

Freeboard
The distance between the top of the hull and the waterline. As the ship is loaded, it sinks deeper into the water so the freeboard is reduced. The positioning of the load line mark is aimed at ensuring the freeboard is the minimum necessary for the safety of the ship.

Structural Strength
The deeper the draft of a ship (the amount of the ship that is underwater), the greater are the loads imposed on the ship's structure. So a ship with a deeper draught requires a higher freeboard.

Compartmentalization and reserve buoyancy
In the event of a casualty, the amount of reserve buoyancy available will depend on how the hull is divided into separate watertight compartments. Compartmentalization is especially critical in the design and construction of passenger ships and special subdivision load lines are assigned for these vessels. If a ship has a greater level of reserve buoyancy, the freeboard can be reduced.

Deck Height
Platform height (the height of the weather deck above the waterline) is a measure of how the vessel may be affected by seas which sweep across the deck.

Transverse Stability
While freeboard does not directly determine the side to side stability of a ship, higher freeboard will allow a ship to roll further before submerging the deck.

Hull Form
Sheer describes the curve between bow and stern. A ship with high freeboard at the bows and stern compared to midships (where freeboard is measured) has more reserve buoyancy.

Fullness
The underwater shape of a hull. A rectangular cross section as on a tanker, is described as "full" and has less reserve buoyancy with the same freeboard than a more rounded hull like that of
tugboat or liner.

Length
A long ship, with only a few feet of freeboard, has less reserve buoyancy than a shorter ship with the same freeboard.

Type of Vessel and Cargo
Tankers and timber carrying ships with buoyant cargoes require less freeboard than a passenger liner or containership.

Season and Zone
Weather conditions normally encountered along a ship's trade route effects its seaworthiness. Ships sailing the North Atlantic in Winter are exposed to much more severe conditions than one sailing around the South Seas.

Further information

Load Lines from National Maritme Museum


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Conventions
Load Lines
Historical background to adoption of Load Lines convention