Fatigue Implicated in Tanker Grounding


By MarEx 2016-03-15 18:49:44

In its investigation report released on Tuesday, the Transportation Safety Board of Canada (TSB) determined that fatigue contributed to helm orders being incorrectly applied causing the tanker Nanny to make bottom contact in Chesterfield Inlet, Nunavut in October 2014. 

No pollution or injuries were reported, but there was damage to the vessel’s ballast tanks, including a crack that allowed water ingress.

Nanny was outbound in darkness in the confined waters of Chesterfield Inlet. To initiate a large course alteration, the master ordered the helmsman to apply port rudder. The helmsman acknowledged the order by repeating it, but turned to starboard instead. Within seconds, the master issued a larger port helm order because the vessel was not responding as he expected. The master then ordered port helm two more times, and the helmsman continued to apply starboard helm until 51 seconds later, the helmsman stated the helm was to starboard and applied the correct port order. 

As the vessel passed its course alteration point, the master took action to slow the vessel down, but the strong tide and the vessel's speed did not allow enough time to prevent the Nanny from touching bottom at Deer Island.

Investigators determined that the master and helmsman were fatigued at the time of the occurrence, and that ineffective fatigue management on board the vessel contributed to their being fatigued while on duty. Neither the master nor the officer of the watch (OOW) noticed the helm direction error, and the OOW had ceased participating in the navigation of the vessel after the master took over, prior to the alteration in course. 

The investigation also identified deficiencies in the vessel's navigational procedures, and in the application of bridge resource management principles.

Despite having a certified and audited safety management system (SMS), the investigation also found several shortcomings with the SMS implementation on board the Nanny which contributed to the occurrence. 

Normal healthy adults need between six and nine hours of uninterrupted sleep each night in order to feel well rested and be able to maintain vigilance throughout the day, says TSB. The average amount of sleep required is between seven and eight hours per night. 

Analysis of the master, helmsman, and OOW's self-reported hours of work and rest all indicated disruptions to their sleep periods. The master was subject to acute and chronic sleep disruption as well as circadian rhythm desynchronization where sleep-wake rhythms (body clock) and the external light-darkness cycle become misaligned. The helmsman was subject to acute and chronic sleep disruption as well as circadian rhythm desynchronization.

The effects of fatigue on performance include slower reaction time, increased risk taking and reduced ability to solve complex problems. The disconnect, by the helmsman, of applying helm in the opposite direction to that ordered, despite acknowledging it correctly, is consistent with reduced attention and a resulting action slip. Furthermore, despite monitoring the helm and the rudder angle indicator, there was a delay on his part in recognizing the error.

While the master detected a delay in the vessel's response to the helm order, he did not attribute this to an error in helm given that the helm order had been acknowledged correctly, his focus was on the radar, there were no visual cues due to the darkness, and there were no lighted aids.

Upon realizing the vessel was not turning to port, the master continued with the plan by repeatedly asking for port rudder without re-evaluating the situation to determine if this would be sufficient to turn the vessel in the diminishing sea room available. The difficulty of the master in assimilating the available information and developing accurate situation awareness is consistent with increased processing time, increased difficulty with problem solving, perseverance with a plan that was not working, and an increased time to react to an emergency.

The report is available here.