For once, our aluminium isn't making waves

When Soflusa Lines, part of Transtejo, planned to upgrade their fleet of fast ferries, they wanted ships capable of carrying 600 passengers at 30 knots. But to protect the river environment and other shipping, Portugese authorities stipulated that the new ships would not be permitted to make a wash higher than 50 cm. The solution: a high technology, low-wash hull, designed and built with aluminium from Hydro.

August 31, 2007

This year, nearly 13 million passengers will cross Lisbon’s River Tagus on fast ferries. It’s a vital commuter link between the north and south banks, and in spite of the construction of parallel road and rail links, many passengers feel the ferries are more convenient.

“Transtejo offers a fundamental, indispensable and quality public service to people who reside on the Tagus' south bank and who need to commute every day to Lisbon,” says CEO of Transtejo, Dr. Jõao Franco.

Transition to a modern fleet

So when it became clear that the Soflusa’s aging fleet of passenger ships dating from the sixties needed replacement, they were looking to improve speed, capacity and comfort for their millions of passengers. The challenge was to combine the technical challenges of large, high-speed craft – without creating huge waves that can have serious implications for river bank erosion and disturbance of other traffic in congested waters. Portugese river authorities imposed a maximum 50cm wave height as a design requirement.

Low-wash design

To solve the problem, Transtejo turned to Damen Shipyards in Gorinchem in the Netherlands, one of the world’s leading constructors of aluminium fast ferries. Through computer modelling and optimization of hull form, they created a ‘low-wash’ catamaran (twin-hulled), waterjet-powered design that was capable of carrying 600 passengers at 30 knots while meeting the maximum wave height requirement – thanks to its lightweight construction in aluminium.

Fast turnaround

But this wasn’t the only challenge to be solved. Since crossings are short and frequent, considerable time can be saved by shortening loading and unloading times. The ships operate 156 crossings per day between Barreiro and Terreiro, a distance of only 5.39 nautical miles – so effective speed can be maintained by keeping turnaround time in port to ten minutes or less. Damen provided the solution by equipping the vessels with extremely wide doors operated by hydraulic rams – thereby also reducing the number of crew required to operate the vessels.

Largest catamaran order since 1986

The result was an order for nine catamarans – the largest catamaran order placed worldwide since 1986 – and construction began at Damen Shipyards in Singapore in March 2002. Damen employ the latest friction-stir welding techniques to save weight and maximize quality, combined with finite element analysis (FEA), an advanced computer-based technique for calculating the strength and behaviour of engineering structures, to guarantee the strength of the ships over their 20-year lifespan. The construction of the nine catamarans required 600 tonnes of aluminium, 6,700 kilometers of welding wire, 18 engines, 28,000 litres of paint, and 5,400 passenger seats. The aluminium plates were supplied by the General Engineering segment of Hydro Aluminium Rolled Products, and were used for both the hulls and the superstructures.

Reduction in journey times

The nine vessels were delivered over a 15-month period from April 2003, to acclaim from passengers and shipowner alike. The new catamarans’ higher speed enabled the timetable to be rewritten – reducing journey times by a third, to only 20 minutes. As Soflusa’s Dr. Franco says, “The catamarans have contributed to a reduction in trip duration and an increase in comfort.” Approximately five million passengers use the new Damen-built ferries on the Barreiro–Terreiro route.

And if you multiply 10 minutes saved by five million passengers a year? Well, you have some idea of how innovative use of aluminium from Hydro is making waves of another kind – by helping to make a more viable society for us all.


Updated: October 11, 2016