Gas fuel is here to stay

The Viking Grace performed faultlessly, while tours of the machinery spaces and views of the bunkering process showed just what a clean fuel, and how straightforward to transfer, is LNG. From our experiences onboard, comparing the exhaust from the funnel of the Viking Grace with any of the other numerous cruise ferries and other ships travelling between Sweden and Finland, the environmental advantages of LNG are obvious. And to judge from the presentations, the economic benefits look equally assured.

However, there was one not-entirely expected advantage over conventional ships. We knew that diesel-electric propulsion confers benefits of lower noise and vibration, so there was no reason to think that gas-powered electric propulsion would be any different. We were not really prepared for the near-total absence of vibration from the engines in gas mode. I should have been better prepared; knowing that these particular Wärtsilä dual-fuel engines run on the Diesel cycle when burning oil and change to the smoother Otto cycle in gas mode. Having felt the difference in vibration myself while standing on an engine in Wärtsilä’s test facility in Vasa while it changed fuels I should have known.

So for applications where noise and vibration are critical, LNG-electric propulsion must come top of the list of choices, even without considering the economics and environment. In fact the only time we were aware that the Viking Grace was moving was when the transverse thrusters were employed during manoeuvring. When will somebody invent the vibration-free side thruster?

In theory, single-fuel engines, such as on the Stavangerfjord, featured in this issue, should be even better. And gas turbines should prove smoother still, if we ever get the change to experience the Incat-built Francisco ferry in South America, with its LNG-fuelled GE LM2500s.

There is another vibration-free propulsion system of course, namely the wind. This too is fast gaining ground as an aid to conventional systems. We looked at it in the last issue; there are more developments this time, and yet more left to be reported in November. Another – like LNG – once-mocked option that now deserves to be taken seriously.