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How Is Water In Double Bottom Tanks & Bilge Spaces Handled?

written by: Ricky • edited by: Lamar Stonecypher • updated: 1/17/2010

This article explains the system for handling ballasting/deballasting operations and the piping arrangement in bilges and db tanks

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    Introduction

    We have learnt about the pipline arrangement on ships and also tips on how to identify pipeline systems used for different purposes such as lubricating oil, sea water and so forth. In this article we will study the general piping arrangement on a ship relating to bilge pipes as well as DB tank pipe fitting arrangement. Basically these types of piping systems are used for ballasting/deballasting operations, flood water removal and bilge water handling.

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    Piping Arrangement

    Bilge Piping Arrangement Regarding the bilge pipes, you can see figure 1 below. As you will notice, there is an elaborate system of pipes which run through the bilges in all areas of the ship. The symbols for the various objects shown in the diagram are as follows

    • Inverted triangle – mud boxes
    • Circles – non return bilge valves
    • Circles with a line diametrically across it – flap valves non return
    • Thick dots – sounding pipes

    The bilge injection valve can be seen towards the bottom of the image somewhere towards the left hand side of the centre portion. The various pumps shown in the picture consist of

    • Bilge pump
    • General Service pump
    • Sanitary pump
    • Ballast pump

    The various areas of the ship have means for suction through some pump or the other and most of the pumps and pipes are interconnected and can be used appropriately as the situation demands either in routine operations or emergency situations.

    Similarly the diagram in figure 2 shows the piping arrangement for the deep tanks of the ship, which are also known as double bottom or db tanks. These are mainly used for ballasting procedures. If you are wondering why are these pipelines not in common which will save cost and equipment; I must tell you that this is mandatory as per IMO regulations that the bilge pipes cannot pass through the DB tanks and they have to be a part of a separate system. In case there is a common pump it should have appropriate isolating arrangement in terms of non return valves or one way cocks.

    DB Tank Pipeline System 

    One such is shown in the diagram and you can notice that it has two pipe connections to it, one for suction and the other for discharge of the sea water. Similarly the ballast pumps can either take water from the sea for delivery to the deep tanks or vice versa depending on whether the ballasting or deballasting operation is required to be performed.

    Important

    An important rule which always needs to be followed in laying down the ballast piping arrangement is that there should not be any possibility of the ballast water to gain access to areas which carry dry cargo. Similarly regulations also state that there should be ample provision to ensure that the water ballast and the fuel of the ship are always isolated from one another.

    Last but not least, I must say that since there are so many types of ships which are used for different purposes, it is not easy to generalize the piping systems in all of them. The above described features fit most aptly on cargo vessels though other type of ships are not much different at least in principle if not in the actual layout of the pipelines.