DRAUGHT MARKS AND SURVEYING

The purpose of a Load line or Plimsoll line is to ensure that a ship has sufficient freeboard (the height from the water line to the main deck) and thus sufficient reserve buoyancy (e.g., the enclosed volume created by the area between the water-line and the main deck-line).

Note : Do Not confuse with Painting Segregation Line.

Normally, the scant draft will be defined as “Painting segregation line” and have same position with full summer load line as below:

Scant draft

Scantling draft is the maximum draft at which the ship can withstand all the loads safely. In other words, it is the draft at which the strength of the ship is built.

It may or may not be equal the tropical draft (Maximum to a ship can load as per load lines).
Let us say a ship’s maximum depth is 15 meters. Its tropical draft is 12 meters. Let us say based on the strength of the ship, we calculate to how much draft this ship can be loaded and still the stresses on the ship will be in safe zone. Let us say we find this draft as 13 meters.
Off course we cannot load upto 13 meters. This is because as per load line convention we can only load upto 12 meters. But if it is safe to load upto 13 meters draft, why we are allowed to load only upto 12 meters. This is because load line drafts are not based Â on the draft that we can load. Rather it is based on the minimum freeboard we need to have at all conditions.

Bow/ Thruster mark

Tug mark:

Answer for the question of Draft mark measurement:

Some case, we can ignore the thickness of bottom if the LCG variate not more than 0.5% in hydro-static calculation upon draft & ship lines (tuyáşżn hĂ¬nh).

For sister vessels, if the difference between lightweightdata is sufficiently small and within the accuracy or tolerance of inclining tests/ lightweight surveys (difference in lightweight is less than 0.5% and difference in LCG is less than 0.5% LBP), the lightweight data of the first vessels may be used for the sister vessel; i.e. identical final stability documentation may be accepted for the sister vessel as for the first vessel.” – DNV rule

9 thoughts on “DRAUGHT MARKS AND SURVEYING”

1. Farhan says:

Hi,

May I know whatâ€™s the tolerance of the position of draft mark during construction in dry dock.

Thanks

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1. Hi, as my experience, The tolerance for each Mark is max Plus (+) 2mm (SOLAS), at dry dock construction, the draft marks should be placed at the designated levels (as closely as possible) Because it will affect directly to the ship loading computer, inclining test (During the testes, all data will be set-up again within tolerance of initial design) after the ship launching. A lot of Design/ Loading data behind and affected by it. As long as the testes are satisfactory with IMO load lines requirement and depend on your yard’s design team experiences and confident.

Further details, you can visit here https://amarineblog.com/2019/08/21/draft-mark-draught-mark-inspection

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