Chief Engineer Hurt Due to Catastrophic Structural Failure of the Vulkan Coupling

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Summary

The vessel sought medical assistance from the Swedish Rescue Centre and the injured crew member was lifted ashore by helicopter.

The Marine Safety Investigation Unit (MSIU) found that immediately prior to the accident, the flexible coupling between the main engine gearbox power take-off and the shaft generator had been incorrectly disassembled (split), following failure of the shaft generator.

Moreover, the safety investigation revealed that the context in which the chief engineer and his sub-ordinates were operating, was intricate enough that possible options were actually either not observed or else not deemed feasible to be considered.

Immediate cause of the accident

The safety investigation revealed that the chief engineer suffered serious injuries as a
result of the catastrophic structural failure of the Vulkan coupling fitted between the
gearbox PTO and the shaft generator.

Technical literature confirmed that any rotating equipment works when it is well
aligned. With the coupling loose on the shaft generator side (albeit without rotating
clearance – Figure 8 below) but still bolted down to the gearbox PTO, a situation had
been created where the full weight of the coupling remained suspended from one end
and unsupported at the other, creating an unavoidable deflection of the coupling body
even because of its inherent flexible characteristics.

The MSIU believes that the above conditions caused a catastrophic structural failure
of the coupling as a result of shaft-coupling misalignment, generating excessive and
severe vibration and extreme imbalance forces when the ME was running at its
operating rpm.

The damaged Vulkan coupling

Findings

  • With the coupling loose on the shaft generator side but still bolted down on the gearbox PTO, a situation had been created where the full weight of the coupling remained suspended from one end and unsupported at the other end, creating an unavoidable deflection of the coupling body even because of its inherent flexible characteristics;
  • The operation of the Vulkan coupling only supported on one side caused a catastrophic structural failure of the coupling as a result of shaft-coupling misalignment, generating excessive and severe vibration and extreme imbalance forces when the engine was running at its operating rpm;
  • The context in which the chief engineer and his sub-ordinates were operating was intricate enough that possible options were actually either not observed or else not deemed feasible to be considered;
  • The removal of Parts 9 and 6 was seen as the safest and most cost effective option;
  • The judgement about risk (and its acceptance) had been jeopardised because neither the chief engineer nor any other crew member was aware that they were actually exposed to risk and / or the actual risk was not observable;
  • The difficulty experienced by the chief engineer and the other crew members was immediate at the perception stage;
  • The crew members on board SCA Munksund had no disconfirming cues correlated to the detection of risk until after the accident happened and hence, their ability to assess real risk was also limited;
  • The situation was misleading to the crew members because the ME was rotated on the turning gear and there were no visible indications of any potential issues;
  • No specific guidelines in the SMS Manual were available for the chief engineer to refer to with respect to the dismantling of the Vulkan coupling.

Distance of 120 mm between the PTO and input shaft

Recommendations

Four recommendations have been issued to the company to ensure that risks associated with the dismantling of similar couplings are better understood.

  • Ensure that Company’s emergency plans within the SMS Manual are developed to address the course of action in the event of a mechanical incapacitation of the shaft generator;
  • Ensure that appropriate signage is displayed on the coupling guard (and other similar couplings), giving a clear warning that they should be disassembled as per Manufacturer’s instructions and the Company’s emergency plans;
  • Issue a clear warning that under no account should the coupling be run ‘split’ by only removing the bolts and spacer ring;
  • Issue guidance on how to best split the coupling to enable it to be run in an emergency.

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Source: Transport Malta

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