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The extraordinary performance of Hatteras Yachts continues to reach new heights as the boat builder expands its resin infusion operations to motoryacht hulls up to 21.9 metres in length.
(Published on September 2007 – JEC Magazine #35)
MR STEVE MARTIN, DIRECTOR OF MARKETING & COMMUNICATIONS, AOC
Compared to hand-laid fibreglass, the resin infusion process gives more consistent part quality. Improved part-to-part consistency ensures a more precise fit of bulkheads, stringers and other structural components. And the higher glass-to-resin ratios associated with resin infusion increase component strength while lowering overall part weight.
All these factors translate into a winning combination of better performance and fuel efficiency for the customer. And because resin infusion is a closed-mould process, emissions in the workplace and into the environment are almost completely eliminated.
Hatteras Yachts is a licensee of SCRIMP® (Seeman Composites Resin Infusion Moulding Process) technology from TPI Technology*. Their initial experience with the process started with bulkheads, athwartships, soles (decks), and other parts. Before transferring their resin infusion experience to hulls, the largest infused part was a 24.6-square-metre deck.
A newly designed 18.3-metre sportfishing convertible was selected for the first resin-infused hull. A large-flanged female mould was built specifically for the infusion technique. In addition to being larger than previously infused parts, the hull is much more complex because it incorporates various design features that achieve a unique combination of speed, comfort and a dry ride.
The legendary company’s progression into resin infusion is getting help from team-oriented technical support and Hydropel® high-performance resin technology from AOC.
In the shop and on the water
For the hull structure, a Hydropel high-performance vinyl ester resin met two primary sets of specifications – one for processing in the shop, the other for performance on the water.
Stringent processing specifications reflect Hatteras Yacht’s resolve to create rugged hulls of the highest structural integrity. The bottom of every hull is a solid, armourlike fibreglass-reinforced composite, which is even stronger when made by the infusion process. PVC foam cores are incorporated in the hull sides and superstructure to deliver high stiffness at a lower weight.
Hull infusion begins with the application of a clear gelcoat and a vinyl ester skin coat into the female mould. Next, fibreglass roll goods cut to precise patterns are laid down, along with PVC foam coring in select sidewall areas. The reinforcement and core are covered with the SCRIMP resin-flow medium.
A layer of polymer film is applied over the dry fibre-core buildup and sealed over the large flanges on the edge of the mould. During resin infusion, 1 bar is pulled to draw resin through the fibreglass reinforcement and create the desired fibre-reinforced composite shape between the mould surface and film. When the entire part has been infused, the resin cures to create a highly densified and repeatable composite structure. The SCRIMP cloth and polymer film are removed after the part cures because nothing superfluous is left in the laminate.
Optimum viscosity and low exotherm
It took a significant amount of developmental work to identify and qualify the infusion resin. Hatteras needed optimum viscosity and open times for filling the 18.3-metre hull in one shot. They also needed to keep the exotherm low for cosmetics while retaining the required structural properties when the part cured.
A dedicated team was able to do all this with the help of AOC. They took a real hands-on approach and followed every step during development. They were there for the initial hull infusions to make sure the requirements were met.
To validate the end-use performance of the Hydropel vinyl ester, Hatteras went beyond the readily available data on resin coupons. Using in-house Instron equipment, the technicians built their own database of flexural, compression and tensile properties on “real world” fibre-resin laminates.
After establishing resin infusion experience with the 18.3-metre hull, engineers and the work crew were ready to infuse the hull of a 21.9-metre motoryacht. The constant thickness and dimensions provided by infusion ensure a precise fit with resininfused structural components. After the infused hull shell is prepared for secondary bonding, the primary PVC foam-cored longitudinal stringers are infused into the hull.
* SCRIMP is a registered trademark of TPI Technology.