International Load Line Convention
LL 1966 as amended by the 1988 Protocol — establishes minimum freeboard requirements and load line marks to prevent overloading and ensure ship stability and safety.
Adopted
1966
In Force
1968
Protocol
1988 Amend.
Contracting States
165
What Is Freeboard?
Freeboard is the distance measured from the waterline to the main deck of the ship. Minimum freeboard is regulated to ensure adequate reserve buoyancy, prevent flooding of the weather deck in heavy seas, and maintain overall ship stability.
The Plimsoll mark (also called load line mark) consists of a circle with a horizontal line through its centre — it shows the maximum permitted waterline for that vessel. Multiple marks indicate the maximum loading in different waters and seasons.
Load Line Marks — The Plimsoll Mark
Lloyd's Register / Load Line
Circle with horizontal line — main load line indicator assigned by classification society.
Summer
Maximum summer load line — applies in Summer Zones as defined in Annex II.
Tropical
Additional freeboard allowed in Tropical Zones — ship may load deeper.
Fresh Water
Fresh water mark — applicable in fresh water (lower density = ship sinks deeper).
Tropical Fresh Water
Deepest permitted load line — tropical fresh water conditions.
Winter
Winter load line — less cargo permitted due to higher sea states expected.
Winter North Atlantic
Applies to vessels under 100m LOA in the North Atlantic during winter season.
Load Line Zones & Areas
| Zone | Mark |
|---|---|
| Summer Zone | S |
| Tropical Zone | T |
| Winter Zone | W |
| Winter North Atlantic | WNA |
| Seasonal Tropical | T (seasonal) |
Application
Applies to all seagoing ships except: