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Ballast quantities as low as 25% of the ship's deadweight may be sufficient for un-docking operations in most ports. Ballasting will continue as the ship departs the unloading port until all the ballast required by the departure ballast plan is on board. In most cases, the draft and trim produced by the SBT or CBT capacity of the ship is sufficient to manoeuvre in port and proceed en route to the next loading port without undue fuel consumption or damage to the vessel. Additional ballast may be taken into the ship's cargo tanks if the master thinks it is necessary for the safety of the ship. This does not mean that the master can ballast dirty cargo tanks to maintain desired speed in adverse weather. The most effective ways to reduce damage in heavy weather are to reduce speed or alter course. Only when these measures have been taken may additional ballast be loaded in the cargo tanks to ensure the safety of the ship.
When it is probable that additional ballast will be needed during the voyage, the appropriate tanks will be required to have been crude oil washed. Ballast water that has been put into a tank that has been crude oil washed, but not water rinsed, shall be regarded as 'dirty ballast' and handled accordingly. This may mean discharging ballast ashore at the end of voyages made entirely within a prohibited zone.
Ballast water shall not be put into tanks that have not been crude oil washed.

2.3.1 Preparing additional tanks for heavy weather ballast
The following typical procedure refers to the IMO example vessel, cargo and ballast systems used to illustrate the CBT operations in section 2.2. While filling the CBT tanks, flush the selected tanks suction piping with clean ballast water and flood the tank bottoms until covered. The following steps are required:

  1. While ballasting No.2 centre and No.4 centre CBT tanks, open valves:
    47 (No.3 centre cargo tank suction and fill valve). 24 (No.1 centre cargo tank suction and fill valve).

  2. Fill each tank to a sufficient innage to cover the entire tank bottom at the existing trim.

  3. Close valves 47 and 24.

  4. When CBT tanks are full, close all valves.

  5. At sea, check the available capacity in the starboard slop tank. Decant slops and/or transfer from starboard slop tank to the port slop tank as necessary to receive the contents of Nos. 1 and 3 centre cargo tanks, and tank washings from those tanks. When finished, close all valves.

  6. Drain the flushing water from cargo tanks 1 and 3. Open valves: 23 (No.1 centre cargo tank stripping suction).
    59 and 60 (No.1 line block valves).
    104 (No.1 line pumproom bulkhead suction).
    144 (No.1 line suction to punp suction block valve).
    124 (Pumproom suction crossover to No.1 pump).
    162 (Stripping manifold valve to suction crossover line).
    163 (Stripping pump discharge valve). 176 (stripper pumproom riser valve).
    233 (Stripping pump discharge to starboard slop tank).

  7. Start the stripping pump and drain No.1 centre cargo tank to the starboard slop tank.

  8. Water wash No.1 centre cargo tank, according to the standard tank washing instructions.

  9. When all washing water is drained from No.1 centre tank, close valve 23.

  10. Open valve 46 (No.3 centre cargo tank stripping suction).

  11. Drain tank flushing water from No.3 centre cargo tank to the starboard slop tank.

  12. Water wash No.3 Centre Tank.

  13. Stop pump and close valve 46.

  14. Flush the No.1 bottom line forward, into the No.2 pipeline, and into the port slop tank as directed when preparing for CBT operations, (steps 7,1 to 7,6 in section 2.2.3).

The centre cargo tanks and No.1 pipeline are now prepared for taking on additional ballast if necessary, without creating a dirty ballast condition which might later delay operations at the loading port or expose the vessel to a pollution claim.
Vessel speed should always be reduced to ease vessel motions before resorting to heavy weather ballast. Speed reduction will:

  • Ease vessel motion,

  • Reduce fuel consumption, and Save the extra fuel consumed for ballasting and de-ballasting operations.
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