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.

At AIM Group, Draft survey of bulk cargo (as well as bagged cargo to recheck shipment weight)

Draft surveys of bulk cargoes are a means of checking that the shipper's figures inserted in the bill of lading are correct. The receiver has paid for the quantity stated in the bill and that figure is prima facie or even conclusive evidence that the amount stated was loaded aboard.

What is a draft survey on bulk carriers?

Draft surveys are convenient and economical means of ascertaining the quantity of cargo loaded or discharged from a ship by reading the vessel's drafts, measuring the ballast water, fuel and diesel oil and other liquids on board, and calculating the final quantity by using the vessel's approved deadweight scales.

What is the procedure for draft survey?

Procedure. The draft survey is performed by reading the ship's draft on the draft markings at six standard points on the hull: forward, midships and aft on both port and starboard sides. Corrections for factors such as trim, water density and non-cargo weight changes are made before calculating the cargo weight change.

How accurate is a draft survey?

Water density fluctuations can greatly affect draft survey accuracy. Draft survey discrepancies can vary by 0.5% to 1.0%. An error of two centimeters in mean draft can result in an error in displacement of about: 68t for Handysize Bulk Carrier (10,000 – 35,000t deadweight).

How is draft calculated?

Raw Draft Calculation; Fore Mean or Fm = (FP+FS)/2, Mid Mean or Mm = (MP+MS)/2, and Fore Mean or Am = (AP+AS)/2. while Apparent Trim or AT = Am – Fm. the Apparent Trim is the Trim that visually find. Draftmark position and correction to perpendicular.

Why is a draft survey required?

Accurately quantify mineral and metal commodities. When transporting cargo on a vessel, draft surveys are conducted to ensure optimized trading of commodities. Surveyors utilize draft surveys to measure draft marks before and after the loading or unloading of shipments.

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