Processes: Dual benefits

Utilising a unique dual-resin and balsa system that includes epoxy infusion, Pantera Yachts achieves all the strength, stiffness and weight savings necessary for its soon-to-launch 76 powercruiser, which, with its largest powertrain, should be capable of speeds of around 55kt. Bob Greenwood reports.

The Pantera 76 GT — the hull design is inspired by Fabio Buzzi’s record-breaking FB80 racing hull.

Given how crowded the large powercruiser market is these days, the launch of yet another new brand could be said to represent a substantial commercial risk. However, it is also said that there is always room in any market for a superior product, which is the rationale behind the new Pantera 76 from new Dutch company Pantera Yachts. Such risks are further reduced when a product includes creative input from three of the top names in the business and the backing of one of the best-known Dutch motoryacht building yards.

It was just over a year ago that Dutch entrepreneur Carl Esch announced that his new company, Pantera Yachts, was going to introduce a series of high-performance cruisers, kicking off with a composite 23m (76ft) model and a subsequent aluminium 33m (108ft). Building of the aluminium model, the Pantera 108, is set to begin this autumn at the Voorschoten, Mulder Shipyard, a company with an important equity stake in Pantera Yachts, the remainder being held by private investors. The first unit is expected to be sea-trialled in autumn 2006. Before then, however, the first composite Pantera 76 is scheduled for delivery in July 2005. When EB visited the new Pantera yard at Waalwijk on March 18, hull number one had already been moulded and hull number two was about to be infused. The deck for boat number one was subsequently infused on March 30. “There has been huge interest in this project,” says Esch, who reveals that four have already been sold and that a deal for a fifth boat is close to signing.

Given that the hull of the 76 was designed by Fabio Buzzi, and that the boat has been externally styled by Cor de Rover and boasts a super lightweight interior by Evan Marshall, expectations for this model are high. With twin 1,500hp MTU V10s, the base GT version is expected to be capable of a top speed well in excess of 40kt, while the top-of-the-range Super Sport version and its twin 2,400hp diesels offers around 55kt. All have Trimax surface-piercing drives and the prices start at E2.6 million, excluding taxes.

To deliver the promised performance, Pantera has taken particular care over the laminate engineering. Indeed, the model’s hull breaks new ground for semi-custom powercruisers of this size. It has an infused dual-resin sandwich around a balsa core. Specifically, the laminate starts with a DSM Neogel ECO gelcoat, onto which a three-ply laminate of chopped strand mat is overlaid by hand with an Atlac vinylester resin. Onto this hand-laid laminate a dry package consisting of various glass layers, Baltek Contourkore and again various glass layers is infused under vacuum with Bakalite epoxy resin. For impact security, the inner and outer epoxy skins are reinforced below the waterline with Aramide woven rovings.

The deck moulding is made in exactly the same way, but without the Aramide.
Pantera asked Arjen Koorevaar of Dutch firm Polyworx to develop a cost-effective production method based on infusion technology for the 76. What Pantera wanted was the strength and rigidity that would enable the model to take the pounding that it would receive at high speeds and avoid the pump effect that can sap the performance and handling of large, fast FRP hulls with single skins. Moreover, Pantera also required the lightness that would help it to reach those speeds. “The big challenge was the bonding of these materials. And the strength of bonding is critical in boats of this speed,” says Koorevaar.

Having spent six months in co-operation with Fabio Buzzi and DSM to get the laminate specification right for the Pantera 76, he was well qualified for the task. If nothing else, the experience was a steep learning curve that was to provide valuable groundwork for the Pantera project. During this time, Koorevaar recalls that Buzzi was “always testing, testing, testing”, and this was all good experience that Koorevaar was able to bring to Pantera. He was able to use it to redesign the lay-up — initially designed for the dual-resin hand-lamination system — to make it suitable for infusion.

Buzzi’s dual-resin system consisted of an outer skin laminated with vinylester, where the last ply is a woven Kevlar sanded to provide a very large surface for the Araldite glue that’s used to bond the balsa core on the laminate. The main reason for developing this system was to combine the cost-effectiveness of a gelcoat with the strength of epoxy.

But while this manual system results in a good bonding between the laminates and the core, it is also very labour intensive. By contrast, with the Pantera system, no Kevlar is used. Instead, after the balsa is sanded, a skin of quadraxial glassfibre is laminated onto this core with epoxy resin under vacuum infusion.

Importantly, Koorevaar was able to feed data from his work with Buzzi into his RTM-Worx flow simulation software for resin transfer moulding and vacuum infusion. It’s this predictive software, with its 3D hull modelling capability, that has enabled Pantera to go from design straight to mould without the need for potentially wasteful trial infusions. This can foretell resin flow rates and absorption through the various areas of mouldings, thus controlling phenomena such as ‘race-tracking’ where resin flow speeds up in indented areas such as chines. It can also compute the amount of filling time needed and the amount of resin that will be used. Given that, unlike with other resins, the curing of epoxy resin cannot be slowed down by adding inhibitors once catalysed, close control of the timing of the process is critical.

As there were no test mouldings as such, small test panels played a vital role in ensuring moulding precision. In fact, Pantera produced more than 60 of them on a vacuum table. Vitally, these showed the Pantera laminate had more than sufficient strength for the job. Indeed, the panels are a lot stronger than they need to be, according to Esch. “With the balsa core I would estimate the force needed to make them sheer could be three or four times higher than a PVC foam of comparable density,” he says.

Koorevaar adds: “The bonding between the vinylester and epoxy is stronger than the vinylester skin. The skin would break first.”

While not compromising the end quality of the moulding, the learning process continues with successive boats. “The first hull took more time than if it had been laid by hand,” admits Esch. “And boat number two will take a similar amount of time as if it had been hand-laid, but the third boat will be much quicker.”
The main delay on hull number two was because Pantera experimented with a two-step infusion plan, trying to increase quality and to save time in fitting the inner dry glass package onto the balsa. “But the fact that the balsa core needed to be completely sanded down after the first infusion with the epoxy resin cancelled out any gains made in fitting time,” Koorevaar explains.

By using peel ply, Esch and Koorevaar are hoping to avoid this time-consuming stage in the process.

In all cases, curing times are the same. The outer skin remains under vacuum for 24 hours and then after the second infusion there’s post-curing at 65°C for more than 20 hours. “This improves quality and avoids any unpleasant surprises such as reinforcement print-through after the boat has been operating for some time in hot countries,” says Koorevaar.

As with any resin infusion, that developed by the Pantera technical team and Koorevaar offers the prime advantages of moulding accuracy, reduced materials wastage and a cleaner working environment — particularly important when working with the chemically aggressive properties of epoxy — compared with traditional wet lay-up. Resin-to-fibre ratios are around 40:60, which means not only less (expensive) resin is used, but that the laminate is stronger too, not to mention the much higher end quality compared to wet lay-up. “The hull area is 214m2,” says Esch. “And in total we use 1,750kg of epoxy.” Only around 200kg of resin left in disposable items such as tubes is wasted.

Compared to conventional wet lamination, Esch reckons that Pantera’s resin-infusion system saves 20 per cent in materials costs, which translates to a 20 per cent saving in the weight of the mouldings.

Set against epoxy pre-pregs, he believes that cost savings are better still, probably 30-40 per cent less. “And then you need a freezer to keep them in and an oven,” he adds.

As regards weight, significant savings will be made in the internal structure of the Pantera 76 owing to the use of bulkheads, fitted furniture and floors with honeycomb cores. Even the installation of a Hamann waste-water treatment plant, neatly housed in the moulded girder system that gives internal structural support to the yacht, is included primarily as a weight saver. Using this, Esch estimates that as much as half a tonne in weight of black and grey water can be recouped.

With a total of 6.5 tonnes of overall weight saved on hull, deck and roof, a Pantera 76 will weigh in at around 38 tonnes overall. “That’s quite a bit lighter than the competition. You could, for instance, have a Pantera 76 with two of the new MTU 10V engines, which produce 1,500hp each, achieving similar performances as the competition fitted with the older and bigger MTU16Vs, which produce 2,000hp each,” he points out.

Certainly orders for the Pantera 76 are promising. Esch says he plans on six boats a year from a single set of tooling.

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