Wednesday, May 25, 2011

Shipping terminology for learners – what is ballast, ballast tank & ballast water ?

Ocean is very deep – a Ship sails on it and conquers it.  There are many terms which bemuse us.  One tries to understand things better by relating the unknown to something simple and is known.  We might book a taxi or lorry and would have to incur the expenditure for its onward movement from the place where it is to our place i.e., paying for the empty leg also to take care of the intended movement from our place to the destination intended.  That is simple but would you imagine loading the vehicle with some weight for providing stability during the onward voyage.  In a horse / bullock drawn cart, the driver ensures that people seat evenly so that weight is distributed and the equilibrium is obtained.

Have you heard of the term ‘ballast’ – ‘ballast tanks’  ‘ballast water’ or the lurking fear that authorities in Chennai had….... Without proper ballasting,  no ship can sail safely.

Ballast, generally, means anything that adds stability or weight.  Sandbags are often used for balancing and obtaining the centre of gravity.  In a ship, ballast is used to add weight for maintaining stability at sea. The primary function of ballast is to keep the ship balanced when there is insufficient cargo weight. A ship also takes on extra ballast when sailing through rough seas in order to increase its stability, or to make the ship settle lower in the water when it needs to pass under a bridge.  Understand that in earlier days, rocks, sandbags, seashells, metal lumps etc., were used to add weight to vessels.  Now most ships use water.  

Ships use the principle of floatation -  the law of buoyancy – the upward thrust  exerted by a fluid, that opposes an object's weight.  When the ship is not carrying the cargo any longer the ship is lighter and requires some weight for maintaining its stability.  So water is taken in, when the intended cargo is loaded on, the water is pumped out, back into the Ocean.  Seems simple but  to think that billions of tonnes of water is transported this way is mindboggling.

Water used for ballast is cheaper and good innovation but tiny microbes can be sucked up with ballast water and potentially become an invasive species. Any form of marine life small enough to be sucked through the pumping system, including microbes, small invertebrates and the eggs and larvae of larger species, can be taken in with the ballast and transferred to another part of the world when the water is discharged.

Ballast water, which can be fresh or saline water,  of course is not carried in the cargo holds. Cargo holds are the revenue earning space of a bulk carrier. Depending on the size, a bulk carrier can have from one to ten cargo holds.   The ballast water is taken in in ballast tanks located at the bottom of the ship.  To do this, one needs ballast system  which consists of the pumps and piping used to fill and empty ballast tanks.  Ballasting on a ship is done through openings provided at the lower most portion of the ship’s hull. The openings are connected to a ballast system through piping. Ship ballast system has dedicated ballast pumps for the ballasting process. For safety purpose, non return valves are provided in the pipelines near the openings to prevent sea water from entering the ship and vice-verse.

The ballast tank which takes and stores water is a compartment within a boat, ship or other floating structure that holds water.   Technically, a ship may have single ballast tank near its center or multiple ballast tanks typically on either side. A large vessel typically will have several ballast tanks including double bottom tanks, wing tanks as well as forepeak and aftpeak tanks. Adding ballast to a vessel lowers its center of gravity, and increases the draft of the vessel.  The lifetime of a ship is greatly influenced by the corrosion conditions, particularly in the ballast tanks.  The ballast tank is an integral part of all submersible vehicles and allows submarines and similar vehicles to rise or drop in the water. 

There was news in Chennai, that the ballast water in ships from Japan spark radiation fears.   It was feared that  Merchant ships from Japan that dock in Chennai could be pumping out contaminated ballast water,posing a health hazard here.   This stemmed from the news that Authorities in Japan had found evidence of severe damage including meltdowns at Fukashima-Daiichi nuclear plants and that  at least 55 million litres of seawater had been used to cool the crippled nuclear reactors and drained back to the ocean,resulting in contamination of sea water around the Fukashima prefecture.

Ships who had loaded ballast water were apprehended to have had the contaminated ballast and brought them here to Chennai. The fear was occasioned by the fact that around four ships visit Chennai every month after sailing through contaminated Japanese waters. Internationally, several  Chinese and European ports have issued alerts over possible radiation contamination due to ballast water from Japanese vessels though  no such alert has been issued in India so far.  

The United States requires all ships traveling in the Great Lakes or the Hudson River above the George Washington Bridge to exchange ballast water in the open ocean prior to entering these waterways.

With regards – S. Sampathkumar.

8 comments:

  1. Good one explaining the concepts too well Sir - Ajay

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  2. I am a regular visitor to your blog and enjoy the way you present your view points - Gupta

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