ASSESSMENT OF SHIP STABILITY

ASSESSMENT OF STABILITY

Stability must be calculated and assessed before sailing. The Master must ensure that the condition of the vessel is within the “permissible standard of stability” this “permissible standard of stability” may be the maximum permissible height of the ship’s KG or the permissible GM or the maximum permissible deadweight moment whichever is appropriate.

It is essential for Masters to be aware that the Standards of Stability obtainable in a vessel are wholly dependent on exposed openings such as hatches, doorways, air pipes and ventilators being securely closed weather tight or in the case of automatic closing appliances such as air pipe ball valves, that these are properly maintained in order to function as designed.

Note: ACTION IS TO BE TAKEN IF SIGNIFICANT DIFFERENCES OCCUR BETWEEN THE DRAFTS OBSERVED AND THAT DERIVED CALCULATED FROM THE SHIP'S CONDITION OF LOADING.

If there is a significant difference between the displacements determined using the observed drafts and that by calculation i.e. by summation of known weights of the ship, its cargo and other items of deadweight, the displacement derived from the observed drafts is paramount. In all cases the displacement obtained should be corrected for density where appropriate. A significant difference in displacement should be taken as that representing more than 2 centimetres difference in mean draft as calculated.

Read: Passage Plane

Where there is a significant difference between the calculated and observed mean drafts such that the displacement obtained by the calculated drafts gives a lesser displacement then the discrepancy shall be treated as an additional increment of cargo weight. This additional increment of cargo weight shall then be assumed to be acting at the mean vertical centre of gravity position for the total cargo weight being carried before the additional of this increment.

If the calculated mean draft gives a greater displacement than that obtained from the observed draughts then the KG of the ship should be that obtained from the calculations of the loading condition but the displacement should be taken as that obtained from the observed drafts.

Any significant differences in the actual drafts as read and that computed must be investigated thoroughly prior to the vessel sailing and a report appended to the departure form noting the outcome of that investigation.