A watertight hatch cover is designed to prevent the passage of water in either direction under a head of water for which the surrounding structure is designed. Many mariners may think hatches are robust, monolithic structures, thereby failing to appreciate the small tolerances on panel alignment and gasket compression. It is better to think of hatches as complex, finely-made structures, to be handled with care. All types of seals, experience dynamic stresses as part of their operational lifetime. For example, 4mm wear on the steel-to-steel contact is sufficient to damage rubber sealing gaskets beyond repair; 5mm sag along the cross-joint can cause a large gap between the compression bar and gasket.
The risk is worsened by the ageing nature of many bulk carrier ships in particular. There is also a degree of bending/deformation that naturally occurs in ships during travel, which puts pressure on hatch covers and can damage sealing. A recent wave of inexperienced crew members has swept across the shipping industry as a cost-saving mechanism, leaving vessel maintenance and hatch cover testing to decrease in quality. While hatch covers are often perceived as indestructible due to their large size and bulky exterior, in reality they are complex, finely made structures that need to be handled with care, a point that many mariners do not realise.
The case study of the Emma Maersk exemplifies the danger of improper servicing. A severe leakage occurred on the container ship in February 2013 when it was loaded with 14,000 containers. The leakage was caused because of a mechanical break-down of a stern thruster, creating the shaft tunnel to flood, as well as leading to severe ingress of water in the aft part. Eventually there was flooding of the main engine room. This was because of non-effective cable penetration sealings, in a sudden blast, four cable penetration sealings in the watertight bulkhead gave way to the water pressure followed by a massive ingress of seawater. Shortly after this, the other three cable penetration sealings also failed, resulting in an even larger ingress of water into the engine room. This led to approximately USD 45 million worth of damages and towage cost.
By greatly reducing the chance of water ingress occurring - it may be possible to save lives, vessel integrity, and cargo at sea - if safer and improved methods of hatch cover testing are implemented. On seafaring vessels and platforms, any doors, hatches and covers on deck are weathertight as, under normal conditions, they will not be submerged and need only prevent water ingress from weather conditions and waves. Internal doors, particularly those which go down the pontoon legs are watertight so sections can be sealed off completely should water ingress occur. The introduction of a continuous watertight integrity monitoring system is the only reliable solution to obtain certainty that the seals are behaving the way they should whether the vessel is at dock or at sea.