Studies claim aluminium vessels more efficient

Rising fuel prices have had a clear impact on all forms of passenger transport and the ferry industry is no exception. It is already well established that, when considering high speed marine transportation, the lighter weight of aluminium construction provides clear economic benefits over steel. Now new design studies undertaken by Australian shipbuilder Austal have highlighted that aluminium vessels also have clear advantages for vessels operating at relatively moderate speeds.

Austal carried out a study on a 65 metre catamaran Ro-Pax ferry with a target operating speed of 14 knots at 350 tonnes deadweight. Two construction alternatives were compared, namely a combination of steel hulls with an aluminium superstructure and all-aluminium construction. Fitted with four Caterpillar 3508 diesel engines each driving a fixed pitch propeller, the steel hulled vessel could achieve the target speed with the engines operating at 85 % of the maximum continuous rating (MCR) of 746kW.

“By contrast the much lighter aluminium vessel requires only 68% of MCR to provide the same performance. This means that the steel ferry will use over 23% more fuel when operating at the same speed,” explains Austal?s Sales and Product Development Manager, Glenn Williams. If these ferries were to operate six voyages per day, 49 weeks per year on a 35 nautical mile shuttle service this could equate to an annual fuel saving of some 630,000 litres.

In addition to substantial savings in fuel and lubricants, the lower engine power output

required for the aluminium vessel produces notable engine maintenance cost benefits.

Analysis by engine manufacturer Caterpillar using a total fuel usage, condition monitoring based maintenance regime shows the time between overhauls (TBO) is extended and scheduled maintenance costs, including replacement of filters and other parts, are reduced “The net effect is that the costs of maintaining the engines on the steel vessel over a 10 year period would be around 12% higher than keeping the same engines in service on the aluminium alternative,” says Glenn Williams. “These savings, and the increased TBO, are further notable rewards for selecting aluminium over steel.”

Based on fuel, parts and labour costs applicable in Australia the total propulsion-related costs of the steel hulled ferry would be over 21% higher than for the aluminium vessel over the first decade of operation.