The Coulombi Egg Oil Tanker - Operations
Better protection, safer and more economical than Double Hull


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COULOMBI EGG crude oil tanker operations is similar to old fashioned single hull.

When the COULOMBI EGG crude oil tanker is loaded, the midship section looks as shown above in the right corner. The three lower cargo tanks and the upper centre cargo tank (pink) (total 16 tanks) are full (98%) of cargo. The permanent top side ballast tanks (light blue) are empty. Daily checks that there are no leaks of crude oil into the ballast tanks are very easy. There are only six tanks to check and their bottoms are flush and the tanks are easy to ventilate. If there is a leak, the cargo oil will collect in the outside, lower corner of the ballast tank and it is fairly easy to pump it back into an undamaged cargo tank. Maintenance work of ballast tank anti-corrosive paint coating is also very easy and touch-up can take place at sea. In principle you only have to access through the deck manhole, descend to the flush ballast tank midheigh deck bottom and then you can close up survey any item from a portable ladder.

The procedure on a Double Hull tanker is more labourious. When the ship is loaded you have to inspect both the double side and bottom spaces daily and they are full of structure, making it a long and dangerous job. The number of ballast tanks may only be eight but they are deep and wide and there are hundreds of manholes to go through to check all cells of these spaces. If there is a leak into the ballast tank of a Double Hull tanker you have a serious problem. How to pump out the oil? How to ventilate the space? How to clean it? How to maintain safety? Leaks into the Double Hull of a VLCC have already taken place several times. The result? Two-four months off-hire, an extremely difficult, expensive and dangerous cleaning operation due to a stupid little crack or pitting damage in the boundary plate (often the inner, 20 mm thick bottom plate of a VLCC).

The writer has seen the result of a double bottom tank flooded by crude oil. After having pumped out the oil and after having tried to ventilate the space for access, we entered through a manhole to have a look - all structures were covered by oil and wax: it was impossible to hold on to any slippery structure: the bottom was slippery due to a mix of oil and mud. The writer slipped and fell after five seconds and was covered in oil, sludge and mud and had big difficulties just the crawl a few metres back to the access manhole. Hydrocarbon gas made breathing difficult. Oil in the eyes made you cry.One (!) mistake we made to inspect the tank was that the boiler suits were normal cotton. The oil penetrated the cotton and stuck to the skin. It took several days just to clean yourself after such a mishap. To clean the double bottom took several months.

The explosion risk of a Double Hull ballast space is ever present. The space is not interted due to, i.a. the problem just to ventilate it. If there is an explosion in the double bottom, it is likely that it will expand forward and aft (and not sideways and up the narrow double sides) and thus blow into the pump room or the engine room. If there is an explosion in a COULOMBI EGG tanker ballast tank (very unlikely), only the upper deck and side will blow off. Similar - the fire risk in a Double Hull ballast space cannot be ignored. The question is how to extinguish a fire in a Double Hull. Probably by filling the space with water, as foam on deck will hardly penetrate down to the double bottom via the double side. Fire extinguishing of a COULOMBI EGG ballast space is easy - you fill the tank with foam from deck.

When the COULOMBI EGG tanker arrives at its discharge port, the procedures are exactly like single hull tanker operations with one major difference. Due to the tank arrangement the COULOMBI EGG can carry three grades of cargo using free flow principles, i.e. pump suctions need only be from the aftermost tanks and the cargo flows there through bulkhead valves. Thus - you do not need cargo suction pipes (the loading is via cargo droplines) except a stripping line. While the cargo is discharged, the tanks are crude oil washed. To wash the lower cargo tanks of a COULOMBI EGG tanker you rely on submerged, fixed machines. With a careful design very little sludge and mud should remain. Manual de-mucking of the lower crude oil cargo tanks is admittedly difficult - the muck is moved to below the access trunks and lifted up. To discharge a Double Hull tanker is similar, but tank cleaning is easier, as there is less structure in the cargo tanks for the cargo to stick to. This is one of the few advantages of smaller Double Hull product or crude oil carriers.

After (or during) discharge the crude oil tanker is ballasted. The COULOMBI EGG tanker is ballasted via pipe lines on deck and droplines and the ballast pump can in principle be located in the engine room. If, for any reason (to prevent biological exchange) you have to change ballast at sea, this is easy with the COULOMBI EGG. You de-ballast by gravity and fill the tank from the top. Ballasting a Double Hull tanker is a little more complicated, depending on the arrangements. Free water surfaces are very large in the double bottom, so you have to check stability. Many Double Hull tankers have lost stability during simultaneously cargo discharge and ballasting and suddenly listed and torn off the cargo hoses. However, the main problem is the mud that accumulates in the double bottom. Over the years several thousand tons of mud may build up in the double bottom of a Double Hull VLCC and reduce cargo carrying capacity. Due to the difficult access into individual cells of the double bottom it is a big job to get the muck out.