From OBO to CABU - the evolution of a concept

In the 1970's (well - lets just say before the Oil Companies invented Vetting Inspectors) a ship design was developed which combined the bulk carrier and oil tanker - the OBO. The OBO was the Ship owners dream, able to carry oil on one voyage and then bulk on the backhaul. The fact that many of these vessels (and their crews) came to a premature end was due to hydrovcarbon gas-generated explosions on the bulk voyage. The 'Berge Istra' literally steamed to the bottom with almost all her crew after a double bottom explosion. The only survivors were two crewman painting on the foredeck and who witnessed (and survived) the spectre of their 227,000 DWT home disappearing beneath their feet.




As OBO's fell out of favour, it appeared that their brief summer would end on the scrapping beaches. Then in the early 1980's the concept was recreated but in a form of a smaller Panamax hull - the PROBO. The PROBO was developed with full width box-shaped which could carry containers, dry bulk and oil. The class had two gantry-mounted cranes for unitised cargo as well as handling the pontoon hatches. Nine of these vessels were built by Hyundai between 1985 and 1989, and continue to trade today.



Oil company vetting policies made alternate trading in dry and wet difficult, and so some of the vessels switched into caustic soda which didn't require Oil Major vetting approvals. Two-way trades developed lifting caustic soda from the Arabian Gulf or North Asia to Australia, and then alumina back. The dry bulk boom of the 2000's drove most of the PROBO's out of wet trading even though they were far from ideal with their box shaped holds.

With the PROBO fleet ageing but with an ongoing niche in the market, Norwegian owner Torvold Klaveness developed the CABU with Oshima Shipbuilding of Japan. The CABU (CAusic BUlk) took the best and most profitable characteristics of the PROBO. No container or unitised cargo capability, or cargo handling gear. The vessels are basically a 7 hold Panamax in which 3 holds (2, 4 and 6) are coated for caustic and equiped with FRAMO deepwell cargo pumps. In bulk carrier configuration, the CABU can load about 65,000 tonnes of heavy ore or coal or as a tanker about 60,000 tonnes of caustic.



So from a concept to miminise ballasting and maximise freight paying tonne-miles, the OBO has evolved from a a problem child into the relatively safe dry and caustic bulk carrier occupying a niche market for the alumina refining industry. With the new Combined Structural Rules (CSR), the CABU design will need to evolve further to incorporate a raised foc's'le head and heavier hatch scantlings. The CABU has given the OBO a new lease of life, but one which is a world away from to original oil and ore carriers on which they were based.

The Antipodean Mariner
24th March 2010