What Are A Ballast System And Ballast Tanks On A Ship?

Ships, over the years, have increased in length, width, height, and cargo-carrying capacity. Despite the immense size, the ballast system which is comprised of ballast tanks allows the ship to safely afloat and navigate.

The ballast system laid out in the entire vessel provides great buoyancy and stability. Ballast tanks include the forepeak tank, wing tanks, double bottom, after peak, and freshwater/drinking water tank.

ballast tank ventilation
ballast tank ventilation

The ballast system is an important function and operation onboard. Hence the creation of a ballast water management system that regulates and monitors ships’ ballast to ensure the environment is safe.

What is a ballast tank?

A ballast tank is an important compartment of the vessel that is filled with water(saltwater/dock water/freshwater) to provide hydrostatic stability. It is used to correct the list and trim of the ship and used during loading and discharging operations.

Different types of ships entail different arrangements of water ballast tanks. For bulk carriers, it includes top side tanks, hopper tanks, and double bottom tanks. Container and tanker vessels have side tanks and double bottom tanks. Roll-on Roll-off vessels and general cargo ships only have double bottom tanks. All ships have after peak and fore peak tanks.

What is a double bottom tank?

The initial design of ships before the Oil Pollution Act of 1990 was a single hull. This means that if a ship experiences grounding or collision, oil or cargo would directly spill into the water. Hence the introduction of the double hull, double-wall, and double bottom tanks in naval architecture.

The watertight compartment located at the bottom of the vessel which is used to carry ballast and provide stability to the ship is called a double bottom tank. These tanks also provide protection in case a ship encounters collision or grounding. Different type of ships entails different arrangement of double bottom tanks.

What is the purpose of the double bottom?

The double bottom creates another layer of protection for the vessel. Compared to the older design of ships wherein they would only have a single hull, double hull or ships with a double bottom are stronger and more stable in navigation.

Another use of double bottom tanks is to carry ballast water for the ship’s trim and stability. A typical Panamax or Kamsarmax bulk carrier would have ten double bottom tanks, five on the port side and another five on the starboard side. Double bottom tanks are either filled up or discharged during cargo operation.

In distress situations like fire in a cargo hold or main deck, double bottom, double hulls or void spaces can be very helpful as it isolates the area affected by the fire. During tank overflow or collision as well as grounding, the double bottom remains an integral structure of the ship.

What is a wing tank?

Wing tanks, also known as top side tanks are ballast tanks on the shoulders/wings of the cargo holds. These tanks are part of the ballast system of the vessel, designed to keep the vessel in the upright position.

A handymax bulk carrier would have ten top-side tanks onboard. These tanks are also considered enclosed spaces. A working permit must be secured before entering such spaces. Crewmen would perform de-rusting and painting on all wing tanks to maintain their structural integrity.

What is the purpose of wing tanks?

Wing tanks are generally used for the ship’s trim and stability. During cargo operation, the Chief officer would monitor the ship’s trim and list as the loading and discharging progress. This would prevent the extreme listing of the vessel or in some restricted ports, touching the bottom due to uneven distribution of cargo.

Included in the ballasting plan is the schedule of either ballasting or deballasting of wing tanks. This would guide officers and crew on deck during cargo operations to know which tanks would be worked on as needed. This would complement the draft survey of the ship as they work on the maximum carrying capacity of the ship.

Freshwater tanks and drinking water tanks are also considered wing tanks. These are located near the engine room and are used to store the drinking water supply of the ship. Because of their size, they have little effect on the ship’s trim and stability.

How are peak tanks used?

Peak tanks, which include the forepeak and after-peak tanks are part of the ballast system onboard vessels. These are located at the forward and aft parts of the ship. The fore peak tank is structured after the bulbous bow and directly below the forecastle deck and chain locker of the anchor.

The after-peak tank on the other hand is designed and installed at the stern part of the vessel, close to the engine room. Peak tanks are used in the ship’s trim and stability. At times, some ports would require vessels to be at either zero trim or trim by the stern. In this case, peak tanks are effective in adjusting the ship’s trim.

How many ballast tanks are there on the ship?

Here are examples of ship ballast tanks layout on two types of ocean-going vessels. Designs may differ, depending on the size of the vessel and owners’ special requirements fulfilled by naval architects.

Panamax Bulk Carrier

Panamax type bulk carrier is a widely used vessel with 5 pairs of double bottom tanks and 7 pairs of topside tanks followed by forepeak, afterpeak, freshwater, and drinking water tanks.

Typical layout of tanks:

Forepeak tank
Port Side#1 Double Bottom tank Starboard side#1 Double Bottom tank
Port Side#2 Double Bottom tank Starboard side#2 Double Bottom tank
Port Side#3 Double Bottom tank Starboard side#3 Double Bottom tank
Port Side#4 Double Bottom tank Starboard side#4 Double Bottom tank
Port Side#5 Double Bottom tank Starboard side#5 Double Bottom tank

Port side#1 Top Side tank Starboard side#1 Topside tank
Port side#2 Top Side tank Starboard side#2 Topside tank
Port side#3 Top Side tank Starboard side#3 Topside tank
Port side#4 Top Side tank Starboard side#4 Topside tank
Port side#5 Top Side tank Starboard side#5 Topside tank
Port side#6 Top Side tank Starboard side#6 Topside tank
Port side#7 Top Side tank Starboard side#7 Topside tank

Port side Drinking water tank Starboard side Freshwater tank
After peak tank

Very Large Crude Carrier

Very large crude oil carriers are less versatile vessels and are commonly built with 5 pairs of double bottom tanks and 5 pairs of topside tanks followed by forepeak, afterpeak, freshwater, and drinking water tanks.

Fore peak tank
Port Side#1 Double Bottom tank Starboard side#1 Double Bottom tank
Port Side#2 Double Bottom tank Starboard side#2 Double Bottom tank
Port Side#3 Double Bottom tank Starboard side#3 Double Bottom tank
Port Side#4 Double Bottom tank Starboard side#4 Double Bottom tank
Port Side#5 Double Bottom tank Starboard side#5 Double Bottom tank

Port side#1 Side tank Starboard side#1 side tank
Port side#2 Side tank Starboard side#2 side tank
Port side#3 Side tank Starboard side#3 Side tank
Port side#4 Side tank Starboard side#4 Side tank
Port side#5 Side tank Starboard side#5 Side tank

Port side Drinking water tank Starboard side Freshwater tank
After peak tank