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