Deadweight (often referred to as Deadweight Tonnage or DWT) is a term used to measure the carrying capacity of a ship . It refers to the difference between the ship's displacement while full and while empty. Put another way, deadweight describes the weight of everything aboard the ship: passengers, crew, cargo, ballast, provisions and fuel. This is an important figure for anyone involved in shipping to understand and is relatively simple to calculate.
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Things you need
- Draft marks
- Calculator or computer
Note down all provisions and cargoes being loaded onto the ship.
Add together the weights of each piece of cargo, each passenger or crew member, and all provisions that have been loaded on-board.
Calculate the weight of fuel. This is done by multiplying the volume of fuel taken aboard by its density. Calculations are commonly done in metric units. Fuel oil has a density of 890 kilograms per cubic meter, meaning that a ship that has loaded 1 cubic meter (or 100 litres) of fuel has added 890 kilograms to its weight.
Add the fuel weight to the weight of cargo, passengers and provisions to calculate total deadweight.
Find the ship's displacement marks. These are white ruler lines on the bottom of the bow and stern of the hull.
Note which displacement line is sitting at the water level before loading the ship.
Load the ship with all crew, cargo, fuel and provisions.
Note which displacement mark is now at the waterline.
Consult the ship's displacement tables, which have formulas to calculate how much water has been displaced based on the shape of the ship's hull. Because the weight of the displaced water is equal to the weight loaded onto the ship, that is the deadweight.
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