The Coulombi Egg Tanker - The M/T 'Prestige' Accident Better protection, safer and more economical than Double Hull

M/T Prestige Start page The Secret  IMO approval  General arrangement and structure  Collision protection  Grounding protection Safety M/T Limburg  M/T Erika The magic Egg USCG approval US Congress

Structural Failure caused Ballast Tank Flooding and heavy Listing The M/T Prestige suffered a fracture in the side shell on 14 November 2002 during a spell of very severe weather outside Spain. The M/T Prestige was a 1976 built Pre-Marpol single hull crude oil tanker that had later been converted only to carry crude and products oil in dedicated cargo tanks and to use some wing tanks for segregated ballast. Cargo in the remaining wing tanks could only be part loaded for hydrostatic balance. She was 26 years old.

At the time of the accident the M/T Prestige carried 77 000 tons of heavy fuel oil (products) and the segregated ballast wing tanks were empty. The cargo wing tanks were part loaded for hydrostatic balance. Very little or no cargo oil spilled out at this time. The damage may have looked like the picture above right! Single hull oil tankers have a fair amount of structural redundancy, if there is a single fracture in, e.g. the side shell. The fracture causes leakage - oil may spill out (this will not happen to a Coulombi Egg tanker - with a crack in the side shell of a lower side cargo tank all oil will be pushed up into an undamaged ballast tank - The magic Egg!) or water may flood an empty ballast wing tank - and generally the local and global stresses are reduced. The fracture will of course grow due to the external wave forces, more cracks may form, but usually you have time to take preventive action.
The preventive action is evidently to immediately seek a calm port of refuge, where the cargo can be transferred , offloaded, to another tanker. When the accident - the fracture in the side shell followed by flooding of an empty ballast wing tank - took place the tanker immediately informed the Spanish authorities. The Spanish authorities unfortunately did not understand that a safe port of refuge was the only solution. Spanish Authorities caused the Oil Spill
They refused the loaded tanker a port of refuge and ordered it further out to sea. The result could only be what followed even if the heavy weather spell calmed out. The fractures in the tanker side structure extended in all directions and on the 18 November about 40 meters of the complete shell shell and 8-10 meters width of the main deck fell off the tanker. Probably the same part of the bottom fell out. Then the global strength of the hull beam was severely reduced and the fractures could easily develop across the full beam - cargo oil started to leak: on the 19 November in the morning the tanker broke into two halves and soon both halves and 77 000 tons were lost. This product (heavy) oil is now slowly leaking out and will pollute the Spanish and French coasts for several years.

Double Hull not the Solution It is widely suggested that double hull tankers will prevent what happened to the M/T Prestige. This is not certain. Double hull tankers have less structural redundancy than single hull tankers and, which is worse, four times more structural surfaces in the ballast spaces (the double hull) to protect against corrosion. Today one coat of epoxy coating is the standard protection; but many 1992-1996 built double hull tankers have already lost their protective coatings in the ballast tanks and have started to corrode. In addition the local and global stresses are generally higher in the double hull structure. A fracture in the side shell of a double hull tanker loaded with product oils will thus result in a similar accident as the M/T Prestige. It must be recalled that double hull and alternative design (the Coulombi Egg is the only alternative!) was mandated by the IMO 1992 to provide better protection than single hull in collisions and groundings only. Protection against structural failures/damage was not considered and there is nothing to say that double hull has better structure than single hull - rather the opposite! Only the Coulombi Egg tanker has better structure than single (and double) hull. The Accident Investigation What caused the M/T Prestige structural failure? We are told that major steel repairs had been carried out 18 months before the accident. The steel repairs require a lot of manual welding and this writer thinks that some defects were introduced via the repair welding, e.g. bad preparation of the welding. This may later cause small fractures, etc. Actually, small fractures occur all the time in oil tanker steel structures and they can only be spotted by regular, visual inspections. If a fracture occurs and an empty ballast tank is flooded or a loaded cargo tank starts to leak oil - these are frequent events - the only solution is evidently to seek a calm port of refuge. The writer has 1973-2006 assisted many tanker owners to avoid oil spills from damaged single - or double - hull tankers and it is why he has developed the Coulombi Egg tanker. The Prestige accident shall be investigated by the Bahamas Authorities as per IMO Resolution A.849(20). Spain, France, Greece and other countries have the right to attend as interested parties/states. It will be an interesting investigation as Spain decided to arrest the Greek Master of the Bahamas flag tanker. Anyway - the investigation shall identify the circumstances of the casualty and establish the causes and contributing factors so that similar incidents are prevented in the future. It should be quite easy - the circumstances? - the tanker suffered leakage and a port of refuge was refused - the causes? - a fracture developed in the tanker structure, the fracture was permitted to extend so that the tanker broke in two - preventive measures? - better quality control of structural tanker repairs, more reliable surveys and quality control, availability of ports of refuge, better oil tankers! Evidently a Coulombi Egg tanker would not have split like the Prestige. The Coulombi Egg Tanker is the only Solution The Coulombi Egg tanker is superior to both single and double hull as described on the page links upper left. First of all there is 70% less structure in the ballast spaces subject to corrosion. Second there is a two-tiers mid-height deck inside the tank body adding extra redundancy in case of a fracture in, e.g. the side shell. But the risk for fractures in the side shell is reduced; the area at risk - below the waterline and the neutral axis (half-depth, D/2, of the tanker) is easy to inspect during loaded voyages (from the mid-height deck in the top side ballast tank). The Coulombi Egg tanker is approved by the IMO since 1997, even if the IMO does not make much publicity about it - as good as or better than double hull as it provides much better collision protection and spills much less oil in groundings. It is also much safer than double hull - easier to ventilate and inspect ballast spaces (no double hull). The Coulombi Egg tanker has also solved the problem of inadvertently transporting aquatic organisms from one part of the world to another in its ballast water. The ballast water is always carried above the (ballast) water line and it can easily be dropped out by gravity during the voyage and replaced by ocean water. You can even go down inside the ballast tank and wash out all sediment. This is evidently impossible in ordinary single or double hull tankers. Double Hull Tankers are not the Solution to prevent future 'Prestige' Type Spills There is no guarantee that double hull tankers will corrode and fracture less than single hull - rather the opposite. Anybody stating that double hull solves the problem does not know what they are talking about. Old single hull tankers are today subject to Condition Assessment Schemes, CAS, and/or Enhanced Survey Procedures, CAP. Both manadate close-up survey of about 100% of the structure in the ballast spaces and 30% of the total structure in the cargo spaces - a very big and difficult job - and everbody knows that you cannot possibly spot all cracks. Double hull requires even more close up-survey as the structure in the double hull ballast space has increased three times. The only - and the best - solution is the IMO approved Coulombi Egg tanker. Contact anders.bjorkman@wanadoo.fr Back to the Coulombi Egg start page!