Module 8 : Ballast Systems

Question 1

What is the purpose of a ballast system?

Answer 1

To pump on, transfer, or discharge sea water when at sea or alongside

Question 2

What is ballast?

Answer 2

Sea water placed in various tanks located throughout the vessel

Question 3

What is the purpose of ballast?

Answer 3

To ensure desired trim, heel, and stability and to maintain structural integrity (prevent hogging or sagging)

Question 4

When will ballasting/deballasting take place?

Answer 4

When loading or unloading the vessel, when fuel is consumed, or when a desired trim is needed (e.g. entering dry-dock).
When ballast is added, they are concerned about:
-> list port/starboard
-> trim fore/aft
-> sinkage/depth (load line)

Question 5

Where are ballast tanks normally located?

Answer 5

In the ship’s sides, port and starboard, as well as in certain sections of the double bottom.
The location and size of the ballast tanks are determined by Nav Arcs during planning. Prior to building a vessel, a set plans with details information on the ballast system, including the stability calculations, will be submitted to a classification society for approval.

Question 6

What regulations are there?

Answer 6

1. Name plates must be fitted to all valves
2. Ballast water may not be carried in tanks intended for fuel oil unless required for the stability of the vessel or for safety reasons
3. Tanks that double as cargo and ballast tanks must have a blank or lock up arrangement to prevent fuel from being pumped through the bilge system or to prevent the cargo from being contaminated with sea water (changeover chest).
4. Ballast pipes shall be constructed of steel with flanged ends
5. Ballast pipes will be constructed in easily removable lengths and be adequately supported against vibration and chafing.
6. Ballast tanks must be fitted with isolation valve (screw down, screw lift)
7. The forepeak may be used for ballast but in instances where the forward collision bulkhead forms the aft section of the forepeak tank, the valve must be able to be remotely operated.
8. Vents, access covers, and sounding pipes shall be fitted to all tanks

Question 7

Bilge & Ballast?

Answer 7

Many of the rules governing ballast systems are similar to those of the bilge system, so the same pump and piping may be used. This cuts down on the amount of piping and machinery in the engine room.

Question 8

How are ballast systems constructed?

Answer 8

In a way to allow one or more tanks to be filled or emptied at the same time.
To fill a tank, the ballast pump will take water from the sea bay (screw down, screw lift valve) and pump it to the respective tank. To empty a tank, the pump will remove the water and pump it overboard (fitted with screw down non return valve). To adjust for list, the engineer will either pump out the side tank or add more ballast to the opposite side tank. However, if the list is adjusted, it’s possible the trim will be affected. Multiple pumping actions may be required.

Question 9

What is the ballast main?

Answer 9

A ballast main is a common line that extends down the length of the vessel. Individual ballast tanks are tied into the main by way of branch pipes. The ballast main and the branch pipes are used to fill or empty the tank.
To remove ballast, valves are opened to connect the suction side of the pump to the ballast main. The appropriate tank valve is opened along with the overboard valve and the tank is emptied.
To fill the tank, the suction side of the pump is supplied with sea water and the discharge pumps to the ballast main. A valve at the respective tank is opened so that it can be filled.
Advantage: simple, not a lot of piping
Disadvantage: multiple pumping actions required to maintain depth & trim

Question 10

Allowing ballast to be transferred directly from tank to tank without filling from the sea or discharging overboard
Called Ballast Transfer System

Answer 10

In this system, there is no ballast main. The branch line from the ballast tank will be piped to a suction and fill valve manifold.
To empty a tank, the appropriate valve on the suction manifold is opened. The suction valve from the pump to the suction manifold is opened and the discharge valve from the pump to the overboard is opened.
To fill a tank, the suction side of the pump is supplied with sea water and the discharge valve to the discharge manifold is opened. The appropriate tank valve on the fill manifold is opened and the tank is filled.
To transfer from tank to tank, the suction side of the pump is connected to the suction manifold and the discharge side of the pump is connected to the fill manifold. The pump now transfers ballast from one tank to another, without loss or gain in total ballast quantity.
Advantage: tank to tank is simple
Disadvantage: more complex system