Therefore, the tables are only as accurate as the closeness of the vessel to its drawings, which leads to variations in the accuracy of individual tank's total volumes as compared to one another. For example; if the bulkhead between two tanks is a few inches off, one tank will be larger and one tank will be smaller than the drawings specify. 2. The other major contributor to this problem is a way in which the deadwood in the tank is accounted for. Deadwood is the internal frames, webs, stiffeners, etc. that supports the shell plating of the tank; and it is usually accounted for in the capacity tables as a straight-line linear deduction. However, on most vessels 70% of the deadwood is located in the lower 25% of the tank, which results in the accuracy of the capacity tables varying with the liquid level in the tank. Typically, volumes in the lower levels of the tank will tend to be overstated or more overstated than volumes at the upper levels of the tank. Considering this, applying a VEF to a part cargo loaded onto a ship where the VEF has been compiled from full or near to full load or discharge figures, is not likely to produce an accurate VEF adjusted ships figure.
• Vessel line fill conditions may have been different at load and discharge port.
7.6 Vessel Measurements
• Clingage, unmeasured ROB and OBQ.
Vessel measurements are a vital part of the transport chain and need to be reviewed as part of any loss or gain investigation. A difference between shore quantity and vessel quantity, adjusted by the VEF, can indicate an inaccurate shore or vessel measurement. When addressing suspected problems with vessel measurements the following issues should be considered:
7.6.1 Vessel Tank Capacity Tables
Vessel capacity tables should be specific to the vessel/tank and carry the date together with notes and corrections for any structural changes, particularly modifications to standpipes and Vapour control valve fittings. Calculations should be checked to verify that trim and list corrections have been applied correctly, as this can have a significant impact on the measured quantities. Ideally a vessel should complete loading as close to even keel and upright as possible to reduce errors in gauging. Nevertheless, even though checks of this nature can be performed, it is well known that shore tank and marine vessel tank capacity tables, in many cases, are not produced to the same level of precision, which results in volumetric differences between ship and shore transferred quantities. There are two primary aspects that are specific to the generation of a vessel's capacity tables that impact on their accuracy: 1. Many ships capacity tables are calculated from the vessel's drawings as opposed to actual measurements.
• Use of non-calibrated measurement equipment.
• Weather and sea conditions.
• Capacity tables may have been incorrect (i.e., for a different gauge point). • Differences between manual and automatic tank gauge (ATG) measurements.
• Trim, list and wedge corrections may not have been correctly applied.
• Gauge height adjustments to allow for retrofitted equipment such as Vapour control valves and closed system fittings may not have been correctly applied. • Different gauge points may have been used at load and discharge.
• Unslotted standpipes may have been used for measurements.
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