Draft Surveys and Weight certification (cargo in bulk and carriers)

Draft (hull)

The draft or draught of a ship is a determined depth of the vessel below the waterline, measured vertically to its hull's lowest—its propellers, or keel.

What is the draft survey of a ship?

Draft surveys are used to determine the weight of bulk cargo such as iron ore, coal, steel scrap, grain and some specific quantities of liquid cargo loaded onto, or discharged from, a vessel.

What is a draft surveyor?

A draft survey is a means of determining the weight of any materials being loaded into (or discharged from) a vessel. AIM's experienced and highly qualified professionals can conduct a draft survey on your behalf and produce an independent draft survey report.

A draft survey is a calculation of the weight of cargo loaded or unloaded to or from a ship from measuring of changes in its displacement.

Why do we do draft surveys?

Draft surveys play a crucial role in determining the quantity of cargo loaded onto a ship. While based on the simple principle of Archimedes' law of floatation, the calculation process can be complex due to the ship's shape, non-linear changes in draft due to hog and sag, and external weather conditions.

What are the factors affecting the draft survey?

Revisions for factors such as trim, water density, and non-cargo weight (such as fuel oil and drinking water) are part of the calculation that we perform. The accuracy of a weight determined by draft survey also depends upon the sea conditions (pitch and swell) at the time of loading or discharge.

How to calculate the draft of a ship?

Assuming that the ship is a cuboids, and that the water it is floating in is fresh and weighs one tonne per cubic metre, you divide the displacement in tonnes by the product of the width and length of the ship in meters and get the draught in meters.

How accurate is the draft survey?

Draft survey calculations accuracy of cargo may vary typically by 0.5% of the cargo loaded on board. This comparison is between cargo on board, calculated by the draft survey, and shore figures of weighted cargo obtained from the port terminals' scale.

Who is responsible for reading the drafts in ship?

Draft marks are used to measure the weight of cargo aboard ship. A person called a draft surveyor together with chef cargo officer read the drafts and make calculations that include the density of the water the ship is floating in and determines the weight of the cargo.