Dear Mr Banerjee,

Look at:

http://en.wikipedia.org/wiki/Tonnage

quote:

Deadweight (often abbreviated as DWT for deadweight tonnes) is the displacement at any loaded condition minus the lightship weight. It includes the crew, passengers, cargo,fuel, water, and stores. Like Displacement, it is often expressed in long tons or in metric tons.

unquote

Although I think the deadweight is always given at maximum loaded condition in sea water (?) ■

Dear Mr Banerjee,

The mass of a ship comprises various groups:

Lightship (Hull, engines, hatches, deckhouses, funnels, piping, pumps, fixed ballast, etc.)

Consumables (fuel, potable water, food stores, ship stores, bunkers, lub oil, removable ballast, etc.)

Crew

Passengers

Cargo

A fully empty (non laden) ship displaces a weight of water, equal to the weight of the light ship.

A fully laden ship displaces a weight of water equal to light ship + consumables + crew + passengers + Cargo.

The dead weight of a ship is then defined as:

The difference in displacement by weight between fully laden ship and light ship =

light ship + consumables + crew + passengers + Cargo – light ship =

consumables + crew + passengers + Cargo.

The non cargo part can be between 5% to 15% of the deadweight, resulting in a somewhat lower cargo capacity than the DWT figure.

DWT is often used to indicate the size of a ship.

This is OK, because Length, Breadth, Depth and Draft of a ship can be estimated fairly well based on DWT

The capacity of an unloader is mostly chosen on basis of the agreed unloading time before demurrage is charged.

The dimensions of an unloader are based on the unloading situation, where the ship size is very important.

The combination of unloader capacity and dimensions are the basis for the unloader structure and equipment and therefore determine the necessary investment and the future operating cost.

In case of an order for an unloader it is best to agree in the contract on a well defined ship.

Sometimes you can unload a bigger (dwt)ship than where the unloader was designed for and sometimes you cannot unload a smaller (dwt)ship.

Best regards

Teus ■