November 2002 - Spain oil spill: single vs double hulls
Key points of the single-hull vs double-hull ships issue
The deadline for phasing out all single-hull tankers is 2015. However, the deadline for phasing out all single-hull tankers without segregated ballast tanks is 2007. Ships with segregated ballast tanks are likely to result in smaller oil spills as the oil is contained in multiple tanks and therefore smaller volumes. The starting date for phasing out single-hull tankers is 2003.
There is an OECD report which suggests that it might be possible to phase out all single-hull tankers sooner than 2015 - maybe by 2010–2012.
However, at the IMO early in 2001, it was a very hard-fought battle to get the 2015 deadline agreed to by all the world's shipping nations. Anything less would have meant unilateral action which would have resulted in the sub-standard vessels operating in parts of the world where they are even less well equipped to handle the ships and the spills.
The US ban
There are double-standards as the US has already banned single hull-vessels in their waters and has stronger liability legislation in their Oil Polllution Act.
The US, however, has a lot of oil tankers on their east coast, which has the types of habitats where a double-hull is likely to be most effective (soft bottoms not rocky shorelines).
It is also worth remembering that double-hulls have their own inherent problems. Many predict that in a few years time we will be seeing massive oil spills from double-hull tankers as the maintenance of a double-hull is more difficult than a single-hull, and there is also a problem with gas build up between the two hulls.
Building double-hull vessels
There is certainly a problem in that many of the world's ship yards have been closed down and therefore there are a limited number of places where new double-hull vessels can be built.
There are also concerns about building vessels too fast and compromising design standards.
The final point is highly relevant as it appears that design standards may have been a factor in the Erika, Nahodka, and Prestige oil spills.
It seems that in the mid-70s in Japanese ship yards, a lot of tankers were produced very quickly and, for some at least, their hulls seem to be "thin".
This itself doesn't appear to be a problem until repairs are carried out which include welding.
There isn't a good deal of supporting information, but it appears that in the case of the Prestige and the Erika, the structural failures occurred some months after welding repairs on their hulls, suggesting this could be a factor in the structural failure of these hulls. But nothing, so far, is proven.