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The largest fibreglass sailing yacht produced by resin infusion in the UK to date is currently being built by Discovery Yachts, at Marchwood, near Southampton, UK, and is fabricated from Scott Bader’s vinyl ester (VE) infusion resin Crystic VE 679-03 in combination with a ‘matched’ marine system using Crystic VE 679PA skincoat and Scott Bader’s new Crystic Permabright D-Iso/NPG high UV performance, marine approved gelcoat.
According to Scott Bader, the transition by Discovery Yachts from traditional wet layup to infusion production for their new Discovery 57 has been driven by the company’s desire to improve the quality and performance of their yachts, to reduce styrene emissions and improve shop floor working conditions.
The hull, which is 57.33ft (17.48 m) long, with a beam of 16.67ft (5.1m) and a 7.67ft (2.35m) draft, was infused using vacuum bagging in one complete, seamless section to precise dimensions and a ‘pre calculated’ 500kg lower composite hull weight. The infusion process has produced a better consolidated laminate, making a stronger yet significantly lighter hull for improved speed; the 500kg saving is a 20% weight reduction. The new Discovery 57 is expected to have its world debut at the Southampton Boat Show in September 2012.
Scott Bader explains that with improving product quality in mind, to provide the highest level of long term gelcoat colour stability, as the first Discovery 57 was ordered in a cream colour, Crystic Permabright D-Iso/NPG polyester gelcoat was selected. It says the Discovery Yachts composites team were convinced by the comparative technical data provided as the test data clearly showed that the advanced D-Iso/NPG polymer chemistry developed by Scott Bader, which uses a deconjugated Iso/NPG polyester backbone in the gelcoat base, has produced a step change technology gelcoat which significantly outperforms established Iso/NPG and Iso gelcoat technologies. Scott Bader claim that independent 12 month Florida UV weathering test results conclusively demonstrated that a white or cream Crystic Permabright D-Iso/NPG polyester gelcoat is able to provide two times better colour stability than the next best in class Iso/NPG gelcoat and four times better than a standard isophthalic gelcoat.
The production process to mould the 57.33ft hull started with the application by hand of the Crystic Permabright gel coat and then Crystic VE 679PA skin coat applied behind the gel coat prior to infusion; the addition of a skincoat provides a gelcoated laminate with optimum osmotic blistering resistance and improved gelcoat aesthetics. However, Scott Bader explains that to achieve the very best gloss finish and eliminate fibre pattern and orange peel in a gelcoat, its ultimate ‘matched marine system’ includes additionally using Crystic Crestacoat 5000PA barriercoat applied immediately behind the gelcoat first and then adding the Crystic VE 679PA skincoat; due to its unique urethane acrylate chemistry, Crestacoat 5000PA not only provides a superior gelcoat finish, but also improves laminate flexibility, so helps prevent gelcoat cracking over time when a vessel is in use, maintaining it show room condition for longer. Discovery Yachts is currently evaluating Crestacoat 5000PA and is seriously considering using it for future decks and hulls as part of their ongoing quality improvement programme.
The next stage was the dry placement of the reinforcement fabrics and Corecell M-Foam core materials in the mould, followed by the peel ply and a flow mesh. Finally the resin lines were laid on the flow mesh and the vacuum bag was placed over the top, which was then sealed to the mould; the size of the moulding required the use of several manifolds for the numerous vacuum lines and resin lines needed to mould the 57.33ft hull in one shot.
The introduction of the infusion process into Discovery Yacht’s production was led by their Production Director, Ben Collett, who over the last nine years has introduced a number of key quality improvement and initiatives in production, such as CNC machining and 3D modelling. Discovery Yachts says it worked in close collaboration with key suppliers Scott Bader for the resins and gelcoat, Gurit SP UK for the core material and Composite Integration for the vacuum infusion pumps, mixing and dispensing equipment.
Ben Collett commented: “When we started looking at infusion, we wanted to find a suitable supplier with matched products for the entire system: gelcoat, skin coat and vinyl ester infusion resin. We looked at a number of options, but Scott Bader was an easy choice even though they had not supplied vinyl ester resins to us before.” Mr Collett added: “The superior colour retention in the Permabright gel coat is a great quality improvement benefit, but Scott Bader not only has excellent quality products, they also provide us with their technical support and experience. More importantly, even though we are not a large account, we have always felt valued and very well supported, so Scott Bader is a valuable partner to us.”
As well as the Discovery 57 hull, Discovery explains that they also now vacuum infuse various internal structural components and floor trays. It says that overall, the switch over from wet-layup to infusion for the Discovery 57 hull has been so successful that there are already plans to start infusing complete decks as well later this year.
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