In June 2013 I reported on the sinking of a DUKW in Liverpool, the second of the year, and in September on the fire aboard a DUKW in London. Oddly enough, it seems that the two accidents had a common element: the foam added inside the hulls to improve buoyancy.
The UK’s Marine Accident Investigation Branch has found that the DUKWs in the Liverpool fleet had not been fitted with enough foam to provide 110% buoyancy, enough to keep the vessel afloat when flooded. MAIB’s tests on the Liverpool vessels
… raised serious questions about whether the operators of DUKWs could fit sufficient foam internally to comply with the current requirement for 110% buoyancy without compromising the safe operation and the practical day to day maintenance of these vehicles.
The “safe operation” part affected the London vessels. In July 2013, a DUKW had to be towed in after a drive shaft universal coupling failed when it overheated and ran dry of lubrication: engine bay temperatures were too high because of the volume of foam inserted. And a report commissioned by the London Fire Brigade into the September fire concluded that:
… the most likely cause of fire was the action of the rotating drive shaft (or other moving parts) on the oil contaminated surfaces of the buoyancy foam blocks.
MAIB has issued a safety bulletin [four-page PDF] with this conclusion:
The MAIB identified significant difficulties in fitting a DUKW with the volume of foam required to meet the buoyancy standards set out in MSN 1699 (M). Further, the nature of these old amphibious vessels, specifically their weight in relation to their size and the complexity of their propulsion arrangements, makes it difficult for operators to comply with the standards applicable to more conventional craft by solely using internal foam buoyancy. An alternative standard, ensuring that DUKWs have the necessary level of damage survivability, therefore needs to be established if they are to be operated safely.
It has recommended that the Maritime and Coastguard Agency should
… ensure that the means used by DUKW operators to achieve the required standard of buoyancy and stability for their vessels does not adversely impact on their safe operation. Furthermore, these vessels should not be permitted to operate until satisfactory levels of safety can be assured under all feasible operating conditions.
The Maritime and Coastguard Agency’s website doesn’t seem to be working, but there is a BBC report here quoting an MCA person as saying
We will not be permitting the vessels to operate until we are satisfied that the necessary safety measures have been achieved.
All of this may help to explain why the VikingSplash DUKWs operating in Dublin are fitted with additional external buoyancy.