4.13 DAMAGE STABILITY, STRESS AND TRIM

4.13.1 Solas requirements
SOLAS Chapter II-1/part 'b' directs that the master must be supplied with the necessary data, information and a procedure that the can rapidly and simply obtain accurate guidance as to the stability of the ship under varying conditions of service. The procedure must include the means of completing a damage stability calculation in sufficient detail to determine the survivability of the ship after damage has occurred.
Part 'b' also requires the provision of an efficient bilge pumping system, and it is the duty of owners and the master to ensure that it is maintained in fully functional condition at all times.
In the event of a casualty, it will be reassuring if the master can have his damage stability calculations verified by an independent calculation. To ensure that his ship's officers have the capability of doing this, the master should regularly assign them to perform a stability calculation . A useful exercise is for the master to give the ship's loading data to a junior officer while on watch, designate a damaged condition to be evaluated and then assume the officer's watch while he works out the damage stability.

4.13.2 MARPOL requirements
MARPOL 73/78 requires a detailed, damaged stability calculation for all new vessels. Vessels comply with the requirements if the result of any damage scenario (within the requirements of regulation 25), leaves the final waterline below all down-flooding openings. On older ships, the master must be aware, and damage stability information provided by the owner should indicate, which deck openings can produce progressive down-flooding and what damage conditions may cause it to occur. Other openings which could produce down-flooding, but which are fitted with watertight closures, must remain closed at all times when not in actual use.

4.13.3 Hull stress and trim correction
The problem of adjusting trim en route under normal conditions has been covered in section 4.3. Adjusting trim following damage requires more care and a thorough examination of the hull stress situation as well. The first concern is that the damaged hull may no longer have the strength it had when intact and the undamaged stress allowance may no longer apply. The second concern is that any list on the ship may be due to negative transverse stability (GM) and must be addressed differently from list due to unsymmetrical flooding.
In combination carriers, it is essential that any action taken to correct a list due to damage should consider the possibility of negative transverse stability. Any countermeasure should correct both the list and potential negative GM.
Calculation of the damage stress condition of the hull may indicate that the hull is over-stressed with respect to normal criteria and certainly over-stressed in its damaged state.
The master may find that he has no recourse to correct this condition unless cargo is discharged/jettisoned overboard. MARPOL regulation 11 recognises this possibility by exempting 'the discharge into the sea of oil or oily mixture necessary for the purpose of securing the safety of the ship or saving life at sea'. If such action is taken, it must be reported and the burden of proof will be on the master to demonstrate by his calculations that the safety of his ship and crew required the discharge of a portion of the cargo to save the venture. When proven to be necessary, the discharge will be treated as a voluntary sacrifice in a general average venture.