10. DIRECT DRAUGHT SURVEY

The direct Draught Survey is an International calculation to compute the weight of the vessel on arrival i.e. prior to commence commercial operation.(Loading or discharging). We suppose that on arrival, the weight of the vessel resulted to be 32.000 metric tons. and when the discharge has been completed the weight resulted to be 12.000. The difference 32.000 - 12.000 = 20.000 is the quantity delivered by the Ship's Master. If we considered the vessel during loading operation, when she completes loading the displacement (i.e. the ship's weight) if resulted to be (for example) 60.000 metric tons, this means that the Master received on board the following quantity: 60.000 - 32.000 = 28.000 metric tons. This calculation is very accurate; Computer uses Archimede law with a max error of only one ton against shore scale errors that can reach 50 tons. This is a valid reason for which owners always require the surveyor to assist the Master in the computation of the direct draught survey.

EXPLANATION OF THE CALCULATION

To be able to carry out Draught Survey calculation it is necessary to know the following data of the vessel:

1) L.B.P. Length Between Perpendiculars.(i.e.distance between the two ship's perpendiculars)
2) L.B.D. Length Between Draught (i.e. distance between forward and after draught read in the immersion line of the vessel. Remember that length between perpendiculars is a constant value of the vessel; instead length between draught is changeable because forward and after draughts are not posted in the same vertical plan. This distance is changeable during loadind or discharging operations. Only few vessels have this distance constant by changing immersion line.
3) DF) DISTANCE FORWARD (i.e. distance between forward perpendicular and the forward draught read at immersion line level.
4) (DA) DISTANCE AFTER ((i.e. distance between after perpendicular and the after draught read at immersion line level.
5)L.C.F. LONGITUDINAL CENTRE OF FLOATATION (i.e. the distance between the centre of buoyancy and the centre of floatation of the vessel.

By inputting all these data, the program will calculate in few seconds the displacement of the vessel corresponding at read draughts with a well coloured printout report. This calculation is to be repeated when the ship will complete commercial operations. The result is a new displacement of the vessel. The difference of the two displacements will give the quantity of cargo delivered to the receivers or the quantity of the cargo received on board.