Introduction To Ship Load Lines
If we try to define Load Line in the most simplest fashion, it will be as follows:
Load line is a special marking positioned amidships which depicts the draft of the vessel and the maximum permitted limit in distinct types of waters to which the ship can be loaded.
As a result of the numerous accidents that has happened at sea due to over-loading of vessels, the significance of having a standard maximum limit for ships was identified long before. However, it took many years from then to have an International agreement for the universal application of Load lines. It was at 1930 when the first International Load Line Convention took place, after which it was periodically amended until the latest one that happened in 2003.
Image Credits: Marine Insight
In order to make a complete comprehension about Load Lines, we must address the following questions:-
- What is the purpose of Load Line?
- Why is it necessary for ships to have Load Lines?
- What exactly is a Load Line?
- What are the marking on a Load line?
- What are the different types of Load Lines?
Purpose and Necessity of Load Lines
The fundamental purpose of a Load Line is to allot a maximum legal limit upto which a ship can be loaded. By prescribing such limits, the risk of having the vessel sailing with inadequate freeboard and buoyancy can be limited. A vessel should be having sufficient freeboard at all times, any exceptions made will result in insufficient stability and excessive stress on the ship’s hull. This is where load lines play an important role, as it makes the task of detecting whether the vessel is over-loaded and it’s freeboard tremendously easy and effortless.
However, since the buoyancy and immersion of the vessel largely depends on the type of water and it’s density, it is not practical to define a standard freeboard limit for the ship at all times. For this reason, the convention has put regulations which divides the world into different geographical zones each having different prescribed load line.
For example, A vessel sailing in Winter on North Atlantic Ocean will have a greater freeboard than on a voyage in Tropical Zones and Fresh waters.
As we have already defined above, Load Line is a special marking positioned amidships. All vessels of 24 meters and more are required to have this Load line marking at the centre position of the length of summer load water line.
There are two types of Load line markings:-
- Standard Load Line marking – This is applicable to all types of vessels.
- Timber Load Line Markings – This is applicable to vessels carrying timber cargo.
These marks shall be punched on the surface of the hull making it visible even if the ship side paint fades out. The marks shall again be painted with white or yellow colour on a dark background / black on a light background. The complete Load line markings consist of 3 vital parts.
- Deck Line – It is a horizontal line measuring 300mm by 25mm. It passes through the upper surface of the freeboard.
- Load Line Disc – It is 300mm diameter and 25mm thick round shaped disc. It is intersected by a horizontal line. The upper edge of the horizontal line marks the ‘Summer salt water line’ also known as ‘Plimsol Line’.
- Load Lines – Load lines are horizontal lines extending forward and aft from a vertical line placed at a distance of 540mm from the centre 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 seasons and circumstances.
Image credits: Welkinridge/ wikimedia
S – Summer :- It is the basic freeboard line at the same level as the Plimsol Line. Other load lines are marked based on this Summer freeboard line.
T – Tropical :- It is 1/48th of summer draft marked above the Summer load line.
W – Winter :- It is 1/48th of summer draft marked below the Summer load line.
WNA – Winter North Atlantic :- It is marked 50mm below the Winter load line. It applies to voyages in North Atlantic ( above 36 degrees of latitude) during winter months.
F – Fresh Water :- It is the summer fresh water load line. The distance between S and F is the Fresh Water Allowance (FWA).
TF – Tropical Fresh Water :- It is the fresh water load line in Tropical. It is marked above the T at an amount equal to FWA.
Timber Load Line Markings
Ships engaged in the timber deck cargo trade are required to have a special set of Load lines known as the Timber Loadlines. Such vessels shall comply with the Code of Safe Practices for Ships Carrying Timber Deck Cargo in construction and other requirements obtaining greater reserve buoyancy and lesser summer freeboard.
Image Credits : Deck Officer Nachiketh Bhattathiri
Timber cargo vessels will have a second set of Load Lines marked similar to the standard load lines positioned 540mm abaft the centre loadline disc.
The letter marking of the timber loadline are different and are prefixed by ‘L’ meaning ‘Lumber’.
LS – Lumber Summer :- Its upper edge marks the summer salt water timber loadline. It is situated at a specified level above the Plimsol line.
LW – Lumber Winter :- It is 1/36th of the lumber summer draft below LS.
LT – Lumber Tropical :- It is 1/48th of the lumber summer draft above LS.
LWNA – Lumber Winter North Atlantic :- It is at the same level as WNA.
LF – Lumber Fresh water :- It is situated above the LS by an amount equal FWA.
LTF – Lumber Tropical Fresh Water :- It is positioned above LT by an amount equal to FWA.
Every ship that has been surveyed and marked in accordance with the present Load line convention are issued by the authorized administration, an International Load Line Certificate. The certificate will have a validity of not more than 5 years and will contain all vital information that includes the assigned freeboard and fresh water allowance.
It is to be noted that, after completion of a load line survey and issuance of the certificate; no changes shall be made to the super structure, markings, equipments or arrangements that has been covered under the survey. If such changes need to be made, the authorized authority conducting the survey shall be contacted.