Fig:BULK CARRIER AMERICAN MARINER UNDERWAY
If any loss of stability becomes evident during loading or discharging, all cargo, ballast and bunker operations must be stopped and a plan prepared to restore positive stability. If the vessel is at a terminal this plan must be agreed with the terminal representative, and with respect to grain loading plant, the hoses are to be disconnected.
The Chief Officer must ensure that the loading or discharging sequence is such that the vessels stability is never compromised and that permitted stress limits are never exceeded. The Master must check and approve all calculations for bending, stress and stability moments of the vessel.
The most critical times are during loading and discharging, during which the bending and stress limits must be carefully monitored. Care must also be exercised, to ensure that the shore installation personnel are adhering to the predetermined loading, or discharging programme.
Caution must also be exercised when loading and discharging, in a way which requires any compartment to remain empty for any stage of the voyage, such as multiple port loading/discharging or carriage of heavy cargoes which require one or more of the vessels holds to be empty.
Stress monitoring system
Some vessels may be fitted with strain/stress gauges, which will automatically alarm at pre-set levels. Whilst this equipment provides valuable information it is essential that an accurate cargo/ballast plan is calculated and that stresses will remain within acceptable limits. The vessel must not be loaded/discharged purely on the strain/stress gauges. If during cargo/ballast operations the stress alarm sounds, all operations must stop until the situation is appraised.
Ballasting and deballasting operations
- Ensure that all ballast tank air-vents are open.
- Sound tank frequently during ballast operations.
- Re-check the soundings after closing the tank and overboard valves as accidental re-filling of tank which was deballasted may occur.
Ballasting and deballasting operations must be carried out under the supervision of the Duty Officer, and are to proceed as per the ballast programme predetermined by the Chief Officer. When there is no ballast console provided in the Cargo Control Room, the Duty Engineer is to control the ballasting operation from the Engine Room. When a ballast console is provided by the Cargo Control Room, the Duty Engineer is to assist in setting the ballast lines, and assisting generally as requested by the Duty Officer. If any problem is encountered which upsets the (de) ballast programme, the Master and Chief Engineer must be informed.
When compiling the ballast programme, the Chief Officer is to take the following into account:
- Draft of the vessel, and the available depth of water.
- Stresses and bending moments likely to be experienced by the vessel during the operation, and to comply with the builders recommended limits.
- Trim of the vessel. If deballasting, the vessel must have enough stern trim to facilitate good suction and efficient stripping. Trim must not be excessive such that it may adversely effect the cargo operations, or place abnormal stress on the conveyor system, especially the Boom or the hatch cover operating equipment. It must also be noted that when discharging, as any trim by the head will place undue stress on the conveyor system. An excessive trim by the stern may cause the belts to mis-train/track; and also cause stress to the Booms slewing mechanism.
- Listing during any SUL operations must always be prevented and a list of up to 1 degree on either side, are the maximum tolerable limits.
- Rate of Loading or discharging the cargo.
- Ships stability.
The Duty Officer is to closely monitor the operation, and keep in close communication with the Duty Engineer, ensuring that all is going according to the predetermined programme. Any abnormalities are to be reported immediately to the Chief Officer. Soundings are to be taken on commencement of pumping a tank, in or out, to ensure that the correct valves have been opened and the correct tank is being pumped. Soundings are also to be taken at regular intervals throughout the operation, to ensure that all is proceeding at the correct rate, and that ample warning is obtained before the need to cease operation or change tanks.
All ballast tank vent/air pipes must be opened and verified before any ballasting / deballasting operations.
Filling of double bottom tanks, hopper-side tanks, or wing tanks, is when possible to by gravitating, to avoid overflow and stress. When topping up a sounding must be taken and the pump stopped, before the water level reaches a maximum.
It must be noted that overflow of ballast may cause wetting damage to the cargo, the shore installation, electrical cables etc. Care must also be taken when discharging into barges as overflowing water can flood them.
When dumping from topside tanks using overboard dump-valves, care must be taken not to dump onto shore installations, barges etc with resultant damage and claims. Also, these types of dump valves must be closed after dumping, in order that water does not re-enter the tanks as the loading proceeds. Defective ballast tank valves must be immediately dealt with and repaired.
All remote operating valves must be operating from the remote position, and the markings of full open and full shut established. The reliance on remote controls of valves must be verified, as a valve could remain partially open, even if the indicator is in the fully shut position.
Fig: Intact stability criteria for dry cargo ships