2.14 LOADING CLEAN BALLAST
When the tank washing operation is complete and the slop tank has
been decanted to provide sufficient room to receive pipeline flushings,
the ship is nearly ready for loading clean ballast. The final preparation
is the flushing of the cargo lines to ensure that only clean water will
reach the cleaned tanks when/if they are filled. The lines should have
been flushed during the washing operation if clean ballast was contemplated,
but a second flush is necessary to be confident that no oil enters the
clean ballast tanks. The following procedure, as with all important
operations, should be prepared in writing by the chief officer and a
record maintained of the dates and times that each step is completed.
To effectively flush the cargo piping, the valves must be set to the
alignment which will be used for filling the ballast tanks, but with
the tank valves closed and the line to the slop tank open. Fill the
line(s) with clean sea water and allow it to set for 30 minutes to float
off any light clingage or trapped oil.
The flushing should be done using a pump which is run at moderate speed.
First thoroughly flush the line to the slop tank, then any branch lines
leading to cargo tanks which have not been washed. If there is any doubt
about the compatibility of the next cargo with the previous grade and
about the effectiveness of the line flushing at the discharge port,
then all cargo lines should be again flushed to their cargo tanks and
the tanks re-stripped to the slop tank. Finally flush the risers and
deck manifold lines. These should contain little or no oil and may be
flushed overboard if the vessel is not in a prohibited zone or any special
area designated by MARPOL. If the risers and deck lines are known to
be dirty or the ship is within a prohibited zone or special area, then
flushing the risers and deck lines can only be done using a hose connected
between the manifold being flushed and a manifold connection which carries
the flushing water to the slop tank (or another accumulation tank).
When the lines are effectively flushed, the ship is ready to load clean
ballast. Clean ballast may be taken on board immediately, or the tanks
may have simply been prepared to load clean ballast in the event that
heavy weather is encountered.
2.14.1 Filling clean ballast tanks
Clean ballast tanks should be filled while the ship is in clean water
(not river water) and carefully inspected while filling. If the tank
shows significant accumulations of oil on the surface of the ballast
while filling, then stop ballasting and empty and rewash the tank. No
sheens or oil should be visible on the surface of the water when the
ballast tank is full.
Ballast tanks must be completely filled to the deck to reduce the mount
of structure exposed to corrosion in the air space above the ballast
2.14.2 Discharging dirty ballast
Dirty ballast must be discharged in accordance with the requirements
of Regulations 9 and 15 of MARPOL. This means that the last one or two
meters of dirty ballast in each tank will be retained on board and transferred
to the slop tank. The available capacity of the slop tank must be compared
to the amount of dirty ballast to be retained. If there is not enough
capacity, then the transfer of dirty ballast residues will need to be
done in stages, with the slop tank allowed to settle and then decanted
Dirty ballast tanks are discharged overboard down to the desired innage
(or until the ODM indicates that the oil content has reached the allowed
limit). The remaining dirty ballast is then transferred to slop tank.
2.14.3 Flushing lines for ballast discharge
When all clean ballast tanks are filled and the dirty ballast has been
discharged and stripped to the slop tank, then the lines and pumps to
be used in discharging the clean ballast must be flushed overboard.
The cargo piping valves must be set exactly as they will be when discharging
clean ballast at the loading port and an amount of ballast run out of
each clean ballast tank using the pump.
2.14.4 Decanting the slop tank
After the slop tank has settled for a sufficient time, it is decanted
as described in Section 2.12.4.