Side shell fatigue is a type of damage that has been brought to the attention of the container industry over the past several years. For example, severe cracking was discovered by German owners beginning in 2003 on Panamax designs after only a few years in service. The problem has been well known with large tankers and bulk carriers for decades, but has only recently been observed to any large extent on containerships. Even though the technical cause of the occurrence is somewhat different from tankers, the cure is much the same.

With the increased use of high tensile steel, fatigue issues must receive constant scrutiny and attention. When the stress level is increased through using high tensile steel, attention must be paid to structural detail and stress concentration factors to maintain the same fatigue life. The problem should have been addressed at the design stage. For ships already built and in operation, fatigue life may be calculated retrospectively and an inspection program established, paying attention to detail before the fatigue life expires. This will allow for budgets and plans to be made and repairs to be carried out in a controlled manner.

Were ship side cracks to occur in a fuel oil tank, this would give rise to an embarrassing oil spill in port resulting in immediate off-hire and repair costs. Such unexpected incidents will certainly have a higher cost than the planned and organized repair.

Side shell fatigue may be caused by a combination of dynamic sea loading and warping deformation in containerships. The use of high tensile steel may lead to decreased fatigue life unless measures are taken to improve the stress concentration factors locally. Such improvements should be implemented at the design and newbuilding stage, but may have to be retrofitted if that is not done. A retrofit can be costly and time consuming, due to the great number of details.

The problem is well known from product tankers with a similar side structure. Warping is not a problem with tankers, but dynamic loading is. This was highlighted on tankers some 10–20 years ago, and much experience has been accumulated on how to deal with it.

For some containership designs, fatigue life is clearly less than what should be expected. In some cases, it may be less than 10 years for world wide trading. In harsh conditions, like the North Atlantic, this may even be reduced further. One must also remember that 34% of containerships are operating in a harsh environment, according to the DNV “World Wide trading” Rule standard.