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
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
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.