The Independent Draught Surveyor from Constellation Marine Services LLc, Dubai had attended recently on a vessel to find out the quantity of Yellow Corn discharged based on Draught Survey calculations.
A Draught Survey is a calculation of the weight of cargo loaded or unloaded to or from a floating vessel from measurements of changes in its displacement before & after loading / discharge. The technique is based on Archimedes’ principle. The draft survey is performed by reading the ship’s draft on the draft markings at six standard points on the hull; forward, mid ship and aft on both port and starboard sides. Corrections for factors such as trim, water density and non-cargo weight changes needs to be considered before calculating the cargo weight change.
Draught surveyor-Brief Description of the vessel’s sea passage
Understand from the Master of the vessel that the present cargo of Yellow corn was loaded on board from Santos Port, Brazil in her all 7 cargo holds. There were 2 parcels of Yellow Corn loaded on board for 2 different discharge ports namely BIK, Iran and Zayed Port, Abu Dhabi. The vessel initially discharged her nominated cargo at BIK from segregated cargo holds and then arrived at Abu Dhabi Port.
Draught surveyor-Initial attendance on board
The Draught Surveyor boarded the vessel at Abu Dhabi for conducting the draught survey. During our attendance, the ship’s draught marks were noted down by us along with the Chief Officer and other related personals. The ship’s ballast tanks, Fresh water tanks and bunker tanks also were inspected & determined the quantity on board. From the ship’s draught marks, calculated the mean of means and noted the displacement value from the hydrostatic table. Also other related values like LCF, TPC & MCTC were noted to apply trim corrections. Density of sea water noted down using a hydrometer and net displacement was calculated.
Draught surveyor-Final attendance on board the vessel
Upon completion of discharge, the final displacement was calculated in the same manner like initial attendance. The difference between the initial & final net displacement of the vessel will be the quantity discharged by the vessel.
A Draught Surveyor is required to carry the equipments like safety torch, measuring devices, draught tubes, Calibrated Steel tape, Sea water sampling bucket or can, calibrated hydrometer and calculator.