Have you ever wondered how ships maintain their stability on the water? Ballast is a key operation surrounding ships, as it is responsible for keeping the vessel upright by ensuring an even distribution of weights.
Generally described as “ballast”, ballasting and deballasting describe the processes of transferring water from the sea to the ship and removing water from the ship to the sea, respectively. But how does this work?
Ballasting and Deballasting: What is it?
In more simple terms, it goes without saying that a ship gets lighter when its cargo is discharged. In these cases, ballast water (basically sea water) is needed to be taken into the vessel’s ballast tanks, to ensure its stability. The ballast water enters the ship’s dedicated ballast tanks, in a procedure known as “ballasting”. These tanks are dedicated to carry only seawater. This process can take place while the ship is unloading its cargo.
Similarly, when the vessel has cargo onboard, the weight of this cargo maintains somehow the stability of the ship, which makes ballast water unnecessary. In these cases, the ballast water is taken out of the ballast tanks, in a procedure known as de-ballasting. This process can take place while the ship is loading its cargo.
Factors affecting ballasting and deballasting
While it may sound like a simple procedure, the reality is usually more complex. For example, not all ships take in or discharge the same amount of ballast water at any point of time, but this depends on several factors, such as:
- Regulation: Environmental concerns surrounding ballast water (see below) may restrict the ship from discharging water in certain areas.
- Cargo or/and ship type: A bulk carrier loading ore will have to discharge more ballast water compared to a ship loading lighter cargo, like paper rolls.
- Weather: During bad weather, it is a common practice to take in more ballast water to ensure as much ship stability as possible.
Procedures on ballasting and deballasting are typically included in the cargo plan. The Chief Officer is usually responsible for decision-making and supervising the ballasting and de-ballasting procedures in line with the cargo operation but is required to be accompanied by Officers-on-Watch (OOW), who practically implement the procedures written in the cargo plan.
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In which cases is it needed?
Cargo loading and unloading is not the only process where ballast is needed. Ballasting and deballasting is also required when the ship is:
- entering a channel
- crossing canals
- to berth.
It becomes understood that ballast is crucial for the safe operation of ships, as it ensures control of its draft and stability, therefore safety at all times, including inclement weather conditions.
Ballasting and deballasting: Key methods
There are two methods used for ballasting and deballasting. One is pumps and the other is gravity. As expected, the latter is the most economical way, as it requires only opening the valves and letting the seawater find its way to the ballast tanks or vice versa. The process works for all tank sizes, regardless of their length, position and area. A key concern here is to prevent the flow limit from exceeding the working limit of the used pipes.
This is why the use of high-capacity ballast pumps is usually more efficient as the pumps are usable at any stage of the operation. Dedicated ballast pumps are installed in the pump room of the ship and are normally used to load or discharge the ballast water. These pumps are capable to take suction from the sea or any of the ballast tank and discharge it overboard or to some other ballast tank. The pump must never get dry or overloaded.
A look into a ship’s ballast system
The ballast system of a ship consists of three main parts:
- the ballast tanks: These are separated from each other but linked to each other through pipes and valves.
- the piping system: This system connects the tanks, the ballast pumps and other peripherals. You can choose which tanks you want to pump water in or out by opening the right valves.
- the high-capacity ballast pumps: These are used to pump water in and out of the ballast water tanks during loading, off-loading and other situations described above.
Ballasting and deballasting: Environmental concerns
Despite being essential for stabilizing vessels at sea, ships’ ballast water is a key environmental threat posed by international shipping. The ballast water taken in on a vessel’s tanks in a specific port in a country can very easily transfer invasive aquatic species -such as bacteria, microbes, small invertebrates, eggs, cysts and larvae of various species- to some other port in another country. The transferred species may survive to establish a reproductive population in the host environment, becoming invasive, out-competing native species and multiplying into pest proportions.
The issue is globally recognized as one of the greatest threats to the ecological and economic wellbeing of the planet for causing enormous damage to biodiversity. To address the issue, the IMO’s BWM Convention, requiring all ships to manage their ballast water, entered into force in 2017. The regulation requires every ship -except for military vessels- to have a ballast water management plan and a ballast water management record book, where every ballasting activity must be recorded.
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