The observed ullage or innage and the vessel's trim some capacity tables show varying TOV values for the same gauge under differing conditions of trim. 8.7.2 Trim Correction This is applied to compensate for the change in liquid level due to the longitudinal plane of the vessel not being horizontal. Subtract the forward draft reading from the after- draft reading. If the trim is positive, that is, the after- draft reading is larger, the vessel is said to be "Trimmed by the Stern". If the trim is negative, that is, the forward draft reading is larger, the vessel is said to be "Trimmed by the Head". The trim correction is found in the vessel's calibration tables and is usually a correction to the observed innage/ ullage. However, it can be a volumetric adjustment to the Total Observed Volume. Trim corrections can be either positive or negative. The trim correction table will state how this correction is to be applied. If trim corrections are not available, it may be possible to calculate this value; however, this is beyond the scope of this level of training. If trim corrections are not available, contact your supervisor for instructions.
8.7.3 List Correction This is applied to compensate for the change in liquid level due to the vertical plane of the vessel not being perpendicular to the horizontal. A vessel's list is usually read from its inclinometer. If such an instrument is not available or there is doubt as to its accuracy, the list can be calculated from the port and starboard amidships draft readings; however, this is beyond the scope of this level of training. If an inclinometer is not available, contact your supervisor for instructions; or, request that the vessel remove the list. List corrections are applied in the same manner as are trim corrections. List corrections can be either positive or negative. The list correction table will state how this correction is to be applied. If list corrections are not available, it may be possible to calculate this value; however, this is beyond the scope of this level of training. If list corrections are not available, contact your supervisor for instructions.
8.7 To Calculate Gross Observed Volume (GOV) – Marine Vessel’s Tanks This is obtained by deducting the free water volume from the Total Observed Volume. GOV = TOV – FW In the event of a volumetric trim or list correction, the calculation is:
GOV = (TOV ± TRIM OR LIST CORRECTION) - (FW ± TRIM, LIST OR WEDGE CORRECTION)
8.7.1 Total Observed Volume (TOV)
This is obtained from the vessel's capacity tables which are entered with one of the following: The observed ullage or innage, if the trim and or list corrections are a volumetric adjustment. The amount of trim and or list correction will need to be applied to the TOV quantity to arrive at a trim and /or list corrected TOV. The trim and /or list corrected ullage or innage.
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