BY THE MARITIME EXECUTIVE 2019-11-13
The Accident Investigation Board of Norway (AIBN) has issued a short interim report about the cruise ship Viking Sky which had a black-out near Hustadvika, Norway, on March 23, 2019 in stormy conditions.
The accident led to 479 passengers being evacuated by helicopter, and the report states:
• The lubricating oil sump tanks of all the diesel generators were maintained at 28–40 percent capacity. MAN’s recommendation was to maintain them at 68–75 percent capacity.
• The diesel generators shut down as a result of the loss of lubricating oil suction due to low sump tank levels, combined with pitching and rolling.
• All three operational diesel generators shut down within 19 minutes of each other, causing blackout and loss of propulsion.
• AIBN estimate that Viking Sky came within a ship’s length of grounding, having passed over or in immediate proximity to 10m shoals before propulsion could be re-established.
Viking Sky’s main propulsion system comprised two fixed pitch propellers directly driven by in-line variable speed electric motors with two three phase stator windings. The voltage at the main switchboard was stepped down from 6.6 kV to 2.2 kV, converted to direct current (DC) and finally inverted to variable alternating current (AC) and frequency, to control the propulsion.
The electric power generation on board Viking Sky comprised four diesel generators (DG) manufactured by MAN Diesels & Turbo. The vessel was equipped with two types of DGs, the small generators (DG1 and DG4) were 5040 kW each, the large generators (DG2 and DG3) were 6720 kW each. Viking Sky had two separate engine rooms, and there were one large and one small DG in each engine room, DG1 and DG2 in the forward engine room and DG3 and DG4 in the aft engine room. Each engine room had its own switchboard which were usually connected by tie breakers to create a single switchboard for power distribution.
On March 16, 2019, DG3’s turbocharger failed rendering the DG inoperable. The day of the blackout, a MAN technician was on board to dismantle the damaged turbocharger in preparation for a replacement to be fitted at the next port.
Events on the Day
On the morning of March 23, between 05:00 and 09:04, 18 lubricating oil low level and low volume alarms were registered by the operational DGs. Each alarm, having been accepted, cleared within a few seconds.
No more alarms were registered until 13:37:04 when DG4 registered an alarm indicating that the DG was shedding load as a result of low lubricating oil pressure. A few seconds later it registered a low lubricating oil pressure alarm. At 13:39:52, DG1 registered a low low lubricating oil sump level alarm. A little over five minutes later, at 13:45:26, DG4 shut down followed by DG2 eight seconds later. DG2 was restarted after approximately 11 minutes, but shut down again along with DG1 at 13:58:31, causing a complete black-out and loss of propulsion.
The bridge team immediately called the engine control room but, at that early stage, the engineers were unsure of the cause, or causes, of the blackout and therefore could not estimate when it would be possible to restore power. The officer on watch called the master, who quickly made his way to the bridge.
Having assessed the situation, the master broadcast a mayday at 1400. He then instructed the crew to drop both anchors. However, the anchors did not hold, and the ship continued to drift astern towards the shore at a speed of 6–7 knots. The General Alarm was activated at 14:13, and the passengers and crew began to muster.
On receipt of the mayday, Southern Norway Joint Rescue Coordination Centre (JRCC) launched a major rescue operation and started scrambling resources, including helicopters, on a large scale.
Restoration of Power
Within 30 seconds of the blackout, the emergency diesel generator started and powered the emergency switchboard. The engineers transferred a total of 10.8 m3 of lubricating oil to the lubricating oil sump tanks of the three operational DGs. They then started DG2 and restored power to the main switchboard, in manual load-sharing mode, at 14:22. At 14:29, the port propulsion motor was re-started and, approximately five minutes later, the starboard propulsion motor was started, providing sufficient propulsive power to maintain slow speed ahead. Over the next hour, DG1 and DG4 were re-started in automatic load-sharing mode, and the starboard propulsion motor was re-started to enable the propulsion motors’ output to maintain between slow ahead and half ahead.
Although the three operational DGs had been restarted, the engineers had to continuously balance the electrical load manually. The vessel was maneuvered towards open waters, still with both anchors lowered.
The first helicopter arrived at approximately 15:00. The crew maneuvered the vessel to head into the weather to give the helicopters the best possible working conditions in order to start evacuating the passengers. The master had considered evacuating passengers and crew to the lifeboats but, given the environmental conditions, this was considered to be too dangerous. The first helicopter hoisting operation took place five minutes later and evacuation of passengers continued until the next morning.
The first tugboat arrived at around 1640. However, the weather conditions were too severe to secure a towline. At 06:30 on March 24, the weather conditions had improved sufficiently to enable tugs to be made fast and towlines were secured fore and aft, although the vessel maintained its own propulsion. At approximately 09:15, the master decided that the vessel was out of danger and that it was safe to stop the evacuation of the passengers. The local Police reported 479 evacuated passengers had been received at the emergency center ashore.
Viking Sky was moored alongside in Molde at around 16:25 on March 24.
All vessel owners and operators are recommended to ensure that engine lubricating oil tank levels are maintained in accordance with engine manufacturer’s instructions and topped up in the event of poor weather being forecast.
Areas of further investigation to be undertaken by the AIBN include:
• Engine room alarm management
• Passage planning
• Decision support
• Lubricating oil management
• Evacuation and LSA
• Safety management
• Local weather conditions and bathymetry
• Safe Return to Port.