Examining Ship Engine Failures on Stormy Seas

When the Viking Sky encountered difficulty and an engine shut down in the storm off the Norwegian coast on Saturday, the freight ship that sailed to its assistance through identical wave conditions also experienced an engine shutdown, raising the possibility of common factors having caused engines to shut down aboard both ships. 

Could excess seawater have entered the engine air intakes of both ships and caused both engines to have shut down? Would there be a future need for air/water separators to prevent seawater from reaching the engine intake manifolds? Or could the occurrence be connected to engine liquids?

Questions need to be asked about the design, installation and location of the fuel tanks. When horizontal fuel tanks are at full capacity and fuel pump intake is at the lowest possible location in the tank, fuel will transfer from fuel tank to engine despite severe pitching and rolling of the vessel. What happens when fuel tank is at less than 50 percent capacity and severe ocean waves cause fuel to flow back and forth at a resonant frequency inside the length of the tank, perhaps for a few seconds leaving only air at the tank outlet?

Severe ocean storms increase ship structural flexing and twisting. During extreme storms at sea, could or did ship hull structural flexing cause breakage of any fuel lines, cause fuel line leakage, cause leakage from the fuel tank or cause a fuel tank to be dislodged from its housing? If the fuel pumps were electrically powered, did storm induced structural flexing disrupt the flow of electric power to the fuel pumps? An evaluation of both ships could provide some insight as to whether storm induced violent ship movements or ship structural flexing contributed to the engines of both vessels shutting down.  

Engine Liquids

Marine engines are cooled by seawater. Under which rare and extraordinary conditions could waves in stormy seas cause a vessel to pitch and roll in a manner to cause air instead of seawater to enter into the engine cooling system? The water pumps for the engine cooling system are designed to pump water instead of air and the result of air having entered the cooling system needs to be explored. Could certain frequencies of vessel pitching cause resonant like back-and-forth movement of engine lubricating oil inside the crankcase or oil tank and what would be the result? 

Under rare and extraordinary conditions involving resonant movement of engine oil in either the crankcase or oil tank, could the intake to the engine oil pump be momentarily exposed to air and what would be the result? It may be technically possible to install baffles inside engine crankcases, inside oil tanks and inside fuel tanks to change the resonant frequency at which liquids would move back-and-forth in response to cyclical inputs caused by the interaction between ocean waves and ship hulls. The installation of additional smaller vertical tanks for fuel, oil and seawater might be considered.

Maintaining Future Engine Power

The cruise ship industry would need to evaluate multiple methods by which to maintain engine operation during extreme sailing conditions. Perhaps an experiment undertaken on one ship could involve the installation of baffles or section dividers in the fuel tanks and oil tanks to reduce resonant back-and-forth movement of liquids inside those tanks during severe sailing conditions. Another possibility could involve adding a small vertical fuel tank between the main horizontal tanks and the engine, with main tanks supplying fuel the vertical tank that would in turn supply fuel to the engine.

Conclusions
   
The fact that the stricken Viking Sky was able to be towed to port after the worst of the storm that shut off its engines, provides opportunity to identify the cause or causes of the shut down and implement the necessary modifications to ensure that in the future, cruise vessels will be able to maintain propulsion during future extreme storms at sea.

Postscript

Courtesy of the ship being towed to port, an initial assessment of the engine failure aboard Viking Sky indicates that the malfunction might have begun in self-contained propulsion units as the ship sailed through rarely encountered extreme wave conditions. The malfunction subsequently caused engines to shut down. Further and more comprehensive investigation is pending.

Correction to Postscript

We had been advised that Viking Sky uses diesel-electric twin-screw propulsion and not steerable electrically powered propellers. 

Ships equipped with direct mechanical drive between engine and propeller have also experienced sudden engine shut downs. Several years ago, a cruise ship sailing off the coast of British Columbia experienced a sudden engine shut-off during a severe tight turn maneuver and while the sea was still calm. One possible explanation is the dynamics of fuel inside either the fuel tank or oil tank as the ship turned. A sudden drop in oil pressure on some engines could trigger an engine shut down, as could lack of fuel flowing from fuel tank to the engine. A quick restart of the engines averted a collision with a rocky coastline.