Draft Survey Accuracy in Surveyor’s Opinion
Ship to ship operation between ship and barge is the most draft survey dispute cases experienced by draft surveyor. This condition is left question; How accurate is draft survey?
By ignorance the accuracy of data provided by vessel and barge (hydrostatic table & tank sounding table), the disputes between ship’s and barge’s draft survey caused by :
– Loading and discharging bulk cargo will cause the cargo spill outs, especially in ship to ship operation.
– Surveyor needs to monitor and estimate cargo spill outs during operation and declares it on the report with photo or video proof.
– After midnight is a critical time with lack of supervision and awareness of operator, when most cargo spill outs was reported.
Nature of cargo
– Bulk cargo that carrying high moisture and hygroscopic are the subject of disputes (trickle losses).
– The high moisture and hygroscopic cargo will release water vapor and become dry under sunlight exposure (if ambient temperature higher than cargo temperature).
– This is undetected due to no physical losses. Sampling cargo and analysis moisture prior and after operation is required. It is need extra effort and cost but it might help.
Skill of draft surveyor
– Sea conditions. The combination of High Swell and Strong Current at anchorage should be examined properly.
– The correctness of Draft Reading, Density Check, and Sounding Deductible should be reviewed.
– Commonly, surveyor is convincing that the vessel data more accurate than barge data. As the vessel is well maintained and documented, the barge not. When disputes happened, they just insisting to recheck the barge. Where as both of them using the same data calibration by Class.
– Surveyor must check the vessel first, as the draft survey on vessel more complicate and involved many factors. Ballast water is the most issues.
Awaiting for comment & feedback.