The need to operate ships both sustainably and more efficiently is a consuming passion for the maritime world today, constantly throwing up innovative ideas. Can anyone think of a better and cleaner way of propelling giant container ships than the huge two-stroke diesels that are relied upon today? A combined gas and steam turbine, such as those found aboard warships, for instance, but with electric drive to the propeller, seems an interesting concept.
We tried gas turbine merchant ships some thirty years ago – think of the Australian ro-ros, some very fast trans-Atlantic container ships and the amazing Baltic express ferry Finnjet. They were all technically successful. Sadly, it was the steeply escalating fuel prices that killed off these vessels prematurely, leaving gas turbines largely to navies. But what if the power and flexibility that gas and steam turbines offer in a compact space can be combined with LNG – the “fuel of the future”? How might this affect the design of very large containerships?
An interesting collaboration between cryogenic engineers GTT, containership giant CMA CGM and classification society DNV GL has resulted in a technical and feasibility study for a new very large containership designed around this LNG fuelled, turbine powered concept.
The design illustrates a number of advantages that emerge from such a propulsion arrangement. Compact and light, while producing an enormous power, the combined gas and steam turbine can be positioned virtually anywhere on the ship and does away with the need for a large engine room stuffed with machinery. The electrical propulsion motors can be positioned near to the propeller shaft they drive. And while the fuel to power efficiency ratios of conventional diesel engines can be up to 52%, a modern land-based combined cycle LNG fuelled power plant will reach efficiencies of 60%.
The downside of LNG as marine fuel has always been sees as the space needed for the storage of the insulated tanks, but the designers have been able to situate two 10,960Cu.m. LNG fuel tanks, with the combined gas and steam turbine installation above them, under the bridge superstructure. These two tanks would provide sufficient range for the ship to make an Asia/Europe round trip between bunkering.
With no engine room to eat into the below-decks cargo space, there would be more room for cargo. And with the electric power generation separate from the electric propulsion, the designers have been given even greater flexibility, the design suggesting three electric main motors can be arranged on one common shaft. Clean fuel, simplified machinery systems with increased redundancy and a high level of safety might also be expected, say the designers to the sort of maintenance strategies that are common practice in the aviation industry. The design is still only a concept, but shows that there is plenty of scope for innovation in the maritime world. Meanwhile, the biggest ever two stroke diesel to be constructed is being installed in another giant container ship in Korea. There is lot for designers to think about !