Composites Manufacturing Magazine

Urban Water Shuttle Uses Sandwich Construction

It looks like smooth sailing for Netherlands-based Damen Shipyards’ new Waterbus 2407 after its May launch. Damen received its first order for four of its urban water shuttles in July from Aqualiner, an urban ferry service provider. The vessels will provide commuter transportation for the port city of Antwerp, Belgium, connecting the center of Antwerp with the southern reaches of the city via the River Scheldt. Eventually, the routes will expand to connect to Antwerp’s northern end, too.

The project results from Damen’s 2013 investment in a composites shipbuilding facility in Antalya, Turkey, where the composites knowledge center joins three other Damen facilities to form a 538,196-square-foot shipyard in a boat-building tax-free zone. “When we first took over the composites factory, there were four people in the building. Now we have 100 employees including composites specialists, engineering project management and support, working in air-conditioned lamination production and material storage areas,” says Marko Paš, Damen’s business development manager for composites.

Vacuum infusion underway for the Waterbus 2407’s first hull at Damen Shipyard’s 161,460-square-foot composites manufacturing facility in Antalya, Turkey. Photo Credit: Damen Shipyards

Damen has built more than 80 aluminum and steel passenger ferries, but this is its first water bus made from composite sandwich construction for the urban transportation market. Model sizes range from 52.6 to 78.9 feet long and accommodate 20 to 120 passengers. The vessel needed to meet several key production and operation objectives, including flexibility, streamlined and efficient manufacturing, passenger comfort, reduced fuel consumption and low cost per seat. That drove the decision to go with GFRP sandwich composites for the hulls, engine room, superstructure and deck.

The GFRP twin hulls reduce water displacement, lower resistance and contribute to speed, energy efficiency and safety. “We conducted testing to compare 5- to 6-millimeter aluminum hull plates with composite sandwich panels, and the composite panels outperformed the aluminum,” says Paš. “When the metal vessel hit floating objects such as debris, the aluminum skin was cut and the hull would take in water. With composite sandwich construction, even when the outer skin was penetrated, the closed-cell core absorbed quite a bit of energy, the inner skin stayed intact and water absorption remained localized.” This is a benefit for use in urban transportation settings, where floating objects are likely to be encountered.

Depending on the loads required and the length of span, the sandwich construction’s PVC foam core ranges from 20 to 40 millimeters thick with an average outer skin thickness of 3 millimeters and inner skin thickness of 2 millimeters. “The growth of the wind energy industry has made the supply of PVC core challenging, so we maintain relationships with both Diab International and Gurit to ensure quick delivery of the core,” Paš says.

The history of the garment making and fiber industry in Antalya means Damen can source directional glass fiber from local suppliers. The company typically gets glass fiber from Turkish company Metyx, a manufacturer of unidirectional, multi-axial and hybrid reinforcement fabrics. Metyx recently announced an increase in its knitting production lines in Turkey to supply an additional 12,000 metric tons of glass and fiber multiaxial fabric knitting capacity to the industry.

Molds for the Waterbus 2407’s modular segments are made by Damen in Antalya using a 3-D milling machine. Manufacturing begins with placement of multiaxial glass fibers into the mold for the outer skin without using a gel coal. “It does mean additional lamination of the outer skin, but we save some 2 kilos per square meter of weight, which is substantial,” notes Paš.

Following placement of core and multiaxial fibers for the inner skin but before impregnation, the construction is placed in a vacuum bag for compaction of the dry fibers and core at an air pressure of 9 tons per square meter (1,843 pounds per square foot), limiting or eliminating gaps between the fibers and core. One-shot vacuum-assisted resin infusion impregnates the core and fibers with epoxy resin.

“Ninety-five percent of the composite components for the Waterbus are handled with one-shot infusion. Vacuum infusion reduces the amount of resin needed, leading to a high-fiber, lower-weight component that helps to prevent water penetration,” says Paš. “We use a computer controlled mixing machine to consistently define the ratio between resin and hardener. With the quantity of resin we process every year, the automation has paid off in less than two years.” The result, he says, is efficient, standardized serial production with a 6-month delivery schedule for the Waterbus – 30 percent shorter than for a comparable metal-welded vessel.

Workers at Damen Shipyards lower a GFRP catamaran hull onto a support stand. Photo Credit: Damen Shipyards

Paš says the use of composites also contributes to the Waterbus 2407’s versatility. “If we want to build efficiently, composites allow for more changes than the aluminum or steel alternative,” Paš says. The modular design of the hulls and deck can be lengthened based on the passenger count specified. The catamaran design provides a large platform to maximize the number of seats, giving operators higher revenue per trip. The composite platform also can be fitted with different finishing styles and levels depending on end use, ranging from benches for basic urban public transportation to luxury finished interiors for sightseeing, dinner cruising, business conferences or lounging.

Fuel costs are a top concern for operators, even with currently reduced fuel prices. The lighter weight GFRP Waterbus 2407 is fitted with a smaller, more cost-efficient engine to achieve a desired speed of 21 knots, lowering fuel consumption. This is an important development for customers in northern Europe, where some cities are aiming for zero emissions in the next five years.

Antwerp’s four urban water shuttles should be delivered by next August, moving the city one step closer to meeting its goals as an innovator in multi-mode transportation.

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