Draft (Draught) Surveys
Draft (draught) surveys are typically used to ascertain the weight of bulk cargoes such as ore, coal, coke, fertilizer, etc. A Draft survey is often the best way (and sometimes the only way) to determine the weight of bulk cargo loaded on or discharged from a vessel. By calculating the initial and final displacement of the vessel (prior to loading or discharging) the weight of the cargo can be determined. In order to produce an accurate weight calculation several factors must be taken into account before the weight of the cargo loaded or discharged can be determined. These include the draft readings of the vessel at several points, the density of the water, the trim of the vessel, the quantity of ballast and other consumables such as fuel and potable water. Reference to the ship's hydrostatic tables is mandatory. An experienced draft surveyor, using internationally accepted methods and procedures should obtain accuracy within 0.5% (½ of 1 %).
For an overview of the basics of draft surveying, click on the following link to an abridged power point presentation in PDF format on draft surveying that was presented by Captain Dan McDonald to the Society of Accredited Marine Surveyors, Annual Conference and Educational Symposia.
Click here for a Sample Draft Survey Report (PDF) sample draft survey report.