Ballast fluid is used to maintain a ship’s stability during voyage, especially when cargo is absent from the hold. Ballasting and de-ballasting operations are fairly common, mostly in ports, cargo transfers and ballast exchanges. Ship stability is therefore, at stake here as the ship’s weight changes at a relatively fast rate and thus may result in serious damage to surrounding facilities as well as the vessel itself.
The fact that stability is at stake gives the first variable to consider; stresses and change over tanks should be considered. Another variable is the watertight integrity when facilities are more prone to flooding during an industrial mission. Examples of consequences related to flooding are the floods of machinery and piping spaces connected to the sea; affecting stability criteria. Vulnerabilities related to maintenance activity, penetrations and mal-operations are other ways a ship’s stability can be affected by flooding. Such effects can be subdued by watertight boundaries.
Stability can also be controlled by simply consulting the stability manual of your vessel as it contains specific information and guidance written for your vessel. This brings the human factor in this equation as mistakes are a guarantee which associates with improper familiarisation. The officers and crew members responsible for the ballasting operations (pumps and valves) must be aware of line-up meanings and machinery of indication; which are provided on diagrams in cargo rooms and pump rooms, requiring ability to differentiate between indications of manual valves and hydraulic suction as well as discharge of steam, electricity or hydraulic pressure.
Finally, the things to consider are faulty gauges and sounding pipes where ballast tanks gauges that work on pneumatic pressure difference methods where a measured pressure of air and difference of counter pressure; giving levels of ballast in tanks and the readings displayed in cargo control rooms through digital, analog readings. These gauges are to be purged regularly and readings should to be compared with manual soundings to eliminate erratic readings. Sounding pipes are often found choked with rags or sounding rods or tapes. They must be clear at all times to get correct manual soundings to ensure the tank is completely empty or intermediate readings are correct in case the gauges are faulty. This will prevent dry running of ballast pumps.
Another aspect to consider before ballasting operations is while carrying out ballasting /de-ballasting operation the pumps in use are mostly of centrifugal type. Starting a centrifugal pump, positive suction pressure must always be kept in mind. The discharge valve of the pump can be kept upto 30% open to prevent damage to the valve body or valve seat ring. The discharge pressures are to be increased slowly and gradually to avoid any pressure surges in the lines and load surges in the engine room as well. Often pressure surges damage the lines and valves. They even cause the load on boiler or generator to fluctuate thus tripping the plant completely and delaying the operation as a consequence. During changeover or brief idle periods during operation pumps can be run in sea-to-sea mode to avoid dry running and over-heating of pump casing or further damage to the pump seal.