It has long been recognized that limitations on the draught to which a ship may be loaded make a significant contribution to her safety. These limits are given in the form of freeboards, which constitute, besides external weathertight and watertight integrity, the main objective of the Convention.
The first International Convention on Load Lines, adopted in 1930, 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.
In the 1966 Load Lines convention, adopted by IMO, provisions are made for determining the freeboard of ships by subdivision and damage stability calculations.
The regulations take 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 Convention includes three annexes.
Annex I is divided into four Chapters:
- Chapter I - General;
- Chapter II - Conditions of assignment of freeboard;
- Chapter III - Freeboards;
- Chapter IV - Special requirements for ships assigned timber freeboards.
Annex II covers Zones, areas and seasonal periods.
Annex III contains certificates, including the International Load Line Certificate.
Various amendments were adopted in 1971, 1975, 1979, and 1983 but they required positive acceptance by two-thirds of Parties and never came into force.
The 1988 Protocol, adopted in November 1988, entered into force on 3 February 2000. As well as harmonizing the Convention's survey and certification requirement with those contained in the SOLAS and MARPOL conventions, the 1988 Protocol revised certain regulations in the technical Annexes to the Load Lines Convention and introduced the tacit amendment procedure, so that amendments adopted will enter into force six months after the deemed date of acceptance unless they are rejected by one-third of Parties. Usually, the date from adoption to deemed acceptance is two years.