What is the Introduction of Ship Load Line?

What is the Introduction of Ship Load Line - Merchant Navy Info - Blog

The load line is a special mark placed in the centre of the ship that indicates the ship’s draft and the maximum permissible limit in the particular sea area in which the ship will be loaded. ‘Draw the load line across the power characteristic curve on the diagram. As you draw, you arrive at a contact point known as a work/rest point or Q point. The importance of uniform maximum limits for ships has been recognized for many years, as many maritime accidents occur at sea due to overloading of ships. However, it took many years to reach an international agreement on the universal use of road lines. It was in 1930 that the first international freeboard competition was held. It has since changed periodically, most recently in 2003.

To Fully Understand Freeboard Lines, You Must Answer the Following Questions:

Purpose and Need for Load Lines 

The concept of load lines was born in the 1870s. In England, to prevent overloading of merchant ships. The basic purpose of a stowage line is to establish the legal maximum limit on which a vessel can be loaded with cargo. By specifying such limits, it is possible to limit the risk of a vessel operating with insufficient freeboard or buoyancy. A vessel must always have sufficient freeboard. Any exceptions will result in not enough stability and undue stress on the hull. The freeboard line plays an important role here, detecting if the ship is overloaded and ensuring that the freeboard remains very comfortable. 

Lloyd’s Register has set minimum freeboard requirements for classified vessels to ensure adequate buoyancy reserve in rough seas. However, it is not practical to always set a standard freeboard limit for a ship, as the buoyancy and immersion of a ship are highly dependent on the type of water and its density. For this reason, the Freeboard Treaty sets out rules for dividing the world into different geographical zones and establishing a prescribed freeboard line for each zone. For example, a ship sailing in the North Atlantic in the winter will have more freeboard than one sailing in tropical or freshwater areas.

Load Line Markings and Types: 

As defined above, load lines are special markings placed in the centre of the ship. All vessels over 24 metres in length must have this loading line marking mid-length at the summer loading waterline.

1 Standard Freeboard Marking – This applies to all ship types.

2 Timber Loading Line Sign – This applies to vessels carrying timber cargo.

These marks must be engraved on the surface of the ship so that they are visible even when the side of the ship is faded in colour. Markings should still be painted white or yellow on a dark background or black on a light background. A complete load line marking consists of three important parts. 

  1. The deck line is a 300mm x 25mm horizontal line. It passes over the top of the freeboard.
  2. The load line disc is a circular disc with a diameter of 300mm and a thickness of 25mm. A horizontal line intersects it. The upper part of the horizon is also known as the “Summer Saltwater Line” or the “Plimsoll Line.

Loading Line 

The loading line is a horizontal line extending forward and backward from a vertical line at a distance of 540 mm from the centre of the disc. The size is 230mm x 23mm. The top of the loading line indicates the maximum depth to which the vessel may be submerged at different times of the year and under different circumstances.

S – Summer:

This is the main freeboard line at the same level as the plimsoll line Additional loading lines will be marked based on the freeboard line this summer.

T – Tropical: 

This is his 1/48 in the summer order, marked above the summer load line.

W – Winter: 

This is 1/48 of the summer order marked below the summer load line.

WNA – Winter North Atlantic: 

Marked 50 mm below winter load line. Applies to winter travel in the North Atlantic (above the 36th parallel).

F – Freshwater: 

This is the summer freshwater stress line. The distance between S and F is the freshwater volume (FWA).

TF – Tropical Freshwater 

It is a tropical freshwater loading line. An amount equal to FWA is marked above the T.

Marking Timber Loading Lines 

Vessels operating in the timber deck cargo trade require their own set of loading lines, known as timber loading lines. Such vessels must comply with the Code of Safe Practice for Vessels Carrying Wooden Deck Cargo and other requirements during construction to provide increased buoyancy reserve and lower freeboard during the summer months. The timber cargo ship has its second loading line marked similarly to the standard loading line and located 540 mm above the central loading disc. The wood loading line has a different letter mark, with the prefix “L” meaning “wood.”

  1. LS – Summer Timber: –Its upper edge shows a summer saltwater timber load It is located at a certain altitude above the Plimsoll line.
  2. LW – Wood Winter: – LS Below is 1/36 of the Wood Summer Draft.
  3. LT – Timber Tropical: – LS Timber Summer Draft 1/48.
  4. LWNA – Lumber Winter North Atlantic: Same level as  – WNA.
  5. LF – Wood Freshwater: – Exceeds LS by an amount equal to FWA.
  6. LTF – Timber Tropical Freshwater: – Exceeds LT by an amount equal to FWA.

International Freeboard Certificate:

All ships inspected and marked in accordance with this Freeboard Convention shall receive an International Freeboard Certificate from the relevant administrative authority. The certificate is valid for up to five years and includes all important information, such as allocated freeboard and freshwater volume. Please note that once a freeboard survey has been completed and a certificate has been issued, no changes may be made to the structure, signage, equipment, or arrangement that is the subject of the survey. If you need to make such changes, you must contact the authorities responsible for the investigation.

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