The Coulombi Egg Oil Tanker - The magic Egg Better protection, safer and more economical than Double Hull
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The COULOMBI EGG tanker design is based on physics and damage statistics and simple strctural design. With top side ballast tanks as collision protection the probability of an oil spill is small - it is only, when the damage extends down into the lower side cargo tank, that an oil spill occurs. Then the sea water flows into the cargo tank and to its undamaged bottom and forces the cargo oil out through the damage in the cargo tank boundary. BUT - even if the COULOMBI EGG tanker is damaged in the side in collision, and the lower cargo side tank is breached, an oil spill may be prevented. MAGIC? Maybe not - below is the result of a test, when water flows in from above into a damaged side cargo tank due to collision or a severe crack due to structural failure. You should know that statistically about 50% of all tanker collision damages are located in the small freeboard area (0.2-0.25D) above waterline only and that the damage then extends downwards. |
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Thus in a collision the lower side tank of a Coulombi Egg tanker will be breached at the top - below water - in the unlikely event that the damage extends so far down. Water will then flow into the cargo tank - to the bottom - and force the oil out ... or? |
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1. The first picture on the right shows a model of a COULOMBI EGG tanker lower side cargo tank full of (black) oil. The tank is 12 web frames long. At the ends are the access trunks from upper deck to the lower side cargo tank. The access trunks (white) are not loaded with cargo. The top of the lower side tank is well below the water line - indicated as a green line on the side of the top side ballast tank (difficult to see on the photo). The 'damage' is blocked by the thumb of the designer/inventor.
2. The next picture on the right shows what happens, when the upper boundary of the cargo tank is breached in collision (or due to a fracture) and water flows into the bottom of the cargo tank (the water at the cargo tank bottom is brownish-yellow due to some oil on the glass model inside). The cargo oil is pressed up into the access trunks (they become black on the picture). No oil leaks out into the sea in this case! Why? The cargo oil is permitted to escape to evacuation tanks (un-damaged top side ballast tanks, which are connected to the access trunks of the cargo tank via escape valves - in the model they are right and left of the damaged top side tank). The system works as long as the damage in the tank side is limited, i.e. the inflow of water does not exceed the capacity of the cargo oil evacuation system through air (actually inert gas). |
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3. The picture to the right shows the evacuation of cargo oil. Water is still flowing into the breached lower side cargo tank, but the inflow of water prevents the oil to spill out through the damage opening. The inflow of sea water is rapid to the bottom of the cargo tank - you can see the turbulence - while the cargo oil escapes - through air - to the rescue tanks via the access trunks.
4. The second picture to theright shows the end of the cargo evacuation - 95% of the oil has been transferred to the rescue tanks. Sea water has filled the whole cargo tank but no oil has spilled into the sea. All the cargo oil is in the evacuation tanks above the breached cargo tank (which in reality should be on the other side of the ship) except some oil between the deck transverse webs. |
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5. The picture right shows the end of the evacuation. The cargo tank is full of water and the water has started to rise in the access trunks. Not one drop of oil was spilled in this simulated collision, even if the side cargo oil tank was breached in its top! The sea water outside the damaged tanker is light blue/green - as it should be. The transfer process can be described by Bernoulli's theorem, when a heavier liquid (water) flows into a lighter liquid (oil), which in turn can flow into another much lighter medium (air - or inert gas) in a tank, which in turn vents to the atmosphere. It is a fascinating balance between the three mediums - water - oil - air. However, if the inflow of water is too rapid, or the escape of oil is too slow, then the oil will flow out against the inflow of water - without mixing - a real oil spill into the environment. |
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When the COULOMBI EGG tanker was approved by the IMO in 1997 as an alternative to double hull, no credit was given to the above shown evacuation system. To be perfectly frank - it was much too sophisticated for the IMO delegates to grasp (except Greenpeace and Friends of the Earth). However - the IMO does not prevent an oil tanker owner to use this system in a COULOMBI EGG oil tanker as collision protection. It is in fact the same transfer system used to prevent oil spills due to tide, when you press up the oil in the bottom cargo tanks after a grounding into the rescue tanks (the top side ballast tanks), where it can be isolated before the tide falls, i.e. the oil will not spill out. Do you consider the above complicated? Today's tanker crews are highly professional and they have a big job looking for leaks (fractures) in double hull tankers - all the time. On a COULOMBI EGG VLCC you do no have to worry about fractures in the structure any more - when they occur they will not flood a double bottom or a double side - they will only result in oil ending up in the evacuation tank (a top side ballast tank) - easy to clean, easy to spot - and the fracture is easy to repair. A simple crack in the double hull structure leading to oil in the double hull space means a lengthy and complicated cleaning operation of the double hull - it will NEVER occur on a COULOMBI EGG tanker (as there is no double hull). Thus - the COULOMBI EGG is a Magic Egg - it does
not spill oil in groundings,
when the bottom is breached and it may not spill oil in
collisions,
even if the side is breached of the lower side cargo tank.
And it does not have a double hull! And it is approved by
the IMO and the European Commission. Contact anders.bjorkman@wanadoo.fr
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