1.3 Load Lines
A Load line is a special marking positioned amidships depicting the maximum permitted draft limits up to which the ship can be loaded in distinct types of waters.
Load line markings are a set of horizontal lines etched amidships on the side of merchant vessels of more than 24 metres in length.
These marks are punched on the surface of the hull, making it visible even if the ship side paint fades out. The marks should however be clearly painted with white or yellow on a dark background or in black on a light background.
There are two types of Load line markings, standard Load Lines, applicable to all types of vessels and timber Load Line Markings, applicable to vessels carrying timber cargo.
Load line markings include 3 essentiel parts:
Deck Line – a horizontal line measuring 300mm by 25mm at the upper surface of the freeboard at the level of the main deck or weather deck.
Load Line Disc and Plimsoll Line - the 300mm diameter and 25mm thick round shaped disc, intersected by a horizontal line. The upper edge of the horizontal line marks the ‘Summer salt Water Line’ (SWL) also known as the Plimsoll Line.
Loading reglementation gained momentum in the 19th century thanks to Samuel Plimsoll, a British reformer. Following hundreds of years of accidents due to overloaded and unsafe ships, Plimsoll campaigned for standardized maritime regulations to prevent future tragedies.
The resulting Plimsoll line, became the cornerstone of the international load line system.
Load Lines and markings – horizontal lines extending forward and aft from a vertical line placed at a distance of 540mm from the center of the disc. They measure 230mm by 23mm.
The upper surfaces of the load lines indicate the maximum depths to which the ships maybe submerged in different water densities, seasons geographical zones.
These zones account for factors like freshwater (F), tropical seawater (T), and winter seas (W).
S – Summer - the basic freeboard line or Plimsoll Line. Other load lines are marked based on this Summer freeboard line.
T – Tropical - 1/48th of summer draft marked above the Summer load line.
W – Winter - 1/48th of summer draft marked below the Summer load line.
WNA – Winter North Atlantic - 50mm below the Winter load line. It applies to voyages in North Atlantic (above 36 degrees of latitude) during winter months.
F – Fresh Water - the summer fresh water load line. The distance between S and F is the Fresh Water Allowance (FWA).
TF – Tropical Fresh Water - the fresh water load line in Tropical. It is marked above the T at an amount equal to FWA.
L - markings for specific loads such as wood (timber or Lumber) (L) might also be present.
Using load lines:
Identify the water type (fresh or salt) and season (summer or winter) where the ship will be operating.
Locate the corresponding load line mark (e.g., S for summer seawater).
When loading, the waterline should not intersect any line above the designated mark, anticipating any changes to water density and geographical zone that may influence the vessels buoyancy. If the ship is overloaded at the port of destination, corrective action may be needed en route.