The purpose of the draft survey is to determine the weight of the cargo on board the vessel. By measuring draft, using the ship’s cargo documentation and information on calculating the ship’s submerged volume, using the density of the water the ship is in, the surveyor can calculate the weight of the ship. The weight of the vessel and other weights on board the vessel, which are not the weight of the cargo, are subtracted from this total amount, the difference is the weight of the cargo. The time for a draft survey depends on many factors: the size of the vessel, the amount of ballast, the number of tanks, and the condition of the vessel. On large vessels, two inspectors usually attend for the production of a draft survey.