An America’s Cup programme would be proud of the build quality of the first Eagle 53 with machined carbon tooling used for all the main components and painstaking attention to detail minimising weight in the areas where material can creep into a build unnoticed – such as edge fillets and (limited) secondary bonds. Eight sections of female tooling were used to make the total 58 monolithic carbon wing ribs (left) with aluminium plants being used to fine tune between the ribs in each grouping. The ‘backpack’ seen in this FEA shot (below) is used to transfer the load from the legs of the shroud attachment ‘top hat’ to the geometric centre of the wing chord
Ribs A defining criterion for the Hybrid Wing was the necessity for extended periods of use without the need to be un-stepped and serviced; our prototype wing had stayed on the platform at a mooring in Bristol Harbor for an entire summer, exposed to the weather and rain for months on end. In a move away from the conventional
carbon/honeycomb rib panels, Paul Bieker floated the concept of thin-skinned mono- lithic top-hat sections. It was agreed that the hat section rib would certainly be more durable, but with 29 ribs to deliver we needed to find a solution to minimise the tooling required for each one. So the 29 ribs were divided into eight
locations: the top hat on the top of the wing, and the mast ball under the foot. When the boat is sailing the aerodynamic forces are applied on the wing, with the structural spar D-section resisting bending and resolving the compression of the stays. The goal of the design is to minimise the
sag of the wing by defining the appropriate stiffness; the challenge for the design team is to come up with the optimum thickness of the wing along the span to achieve a satisfactory structural stability. In the con- struction process the appropriate stiffness was achieved thanks to extensive use of high-modulus carbon unidirectional stacks in the corners of the D-section. When the boat is back from sailing the
sails are lowered. Unlike a conventional sailboat, the sail is not stored on a boom. The sail must be taken off the rig so that the wing can then rotate freely. On Caliente the size of the mainsail made
it manageable to use bolt ropes, but the much larger Hybrid Wing on the Eagle 53 features track and cars. However, during our brainstorming we came up with the principle of a removable lower trailing edge on the wing; now when the sail is lowered the sail and cars are stacked on a section of the trailing edge that can be disassembled from the wing completely making the de-rigging process a lot neater. The design of the Hybrid Wing was an
interesting and unique challenge. It was a fruitful collaborative process that ended up in a beautiful result thanks to all of the talented people involved.
INTO PRACTICE – Wolfgang Chamberlain, Fast Forward Composites The Hybrid Wing D-section is split into a top and bottom section, each section being approximately 40ft long. Considering the chord length of the sections, particularly the wider lower section, we decided to split the tooling at centreline to allow for easier access to the forward extents of the ‘D’. We modelled the sections into 10ft tooling blocks and cut direct female tools on our Ares CMS five-axis mill. We then joined our existing laminating
tables together to create a beautiful single carbon surface measuring 10ft wide and 60ft long. The upper section tooling blocks were assembled on our tables and we were then able to process the D-sections and the shear web in the same cure cycle sequence. Pre-release of the cured outside skins
was a concern for us, so we modelled some features into our tooling to help distribute the vacuum across the surface of the cured outside skin. We then roll-formed honey- comb core over an alloy tool to complete the inside skin laminate. To give ourselves more time to assemble
the top hat bearing structure we built the upper D-section first. Once the upper sec- tion components were completed we moved them to the assembly jig where we joined the right and left halves and installed the ribs and shear web. With the tables cleared, the lower D-section could be started while the top hat/upper D-section connections were manufactured and assembled.
sections of female tooling. Using carefully machined aluminium plants, we were then able to modify the trailing edge details for each rib. For the shorter ribs we changed the angle of the plant and moved it closer to the interface with the D-section. Thus each rib tool could be used to fabricate three or four sections. Once laminated, the ribs would be
loaded into the autoclave and cycled overnight en masse. The fabrication of the ribs, 58 in total, happened in parallel to the lamination and assembly of the D-sections to which they would attach.
Assembly The upper and lower D-sections were assembled on a CNC-cut jig. To minimise the hinging moment at the interface of each rib and the shear web, the ribs extended approximately 200mm into the D-section. After the ribs were bonded on, the shear web was notched and carefully slid up from the bottom of the D and rotated into place on pre-formed D-section flanges. Trailing- edge sections and the top-hat bearing struc- ture were installed and the finished sections were prepared to ship to the Caribbean.
Splice The upper and lower sections of the wing were spliced together in the same fashion as the Cup wings using titanium side and forward splice plates. All of our titanium work for the wing was supplied by Alpine Machine in Arlington, WA, while WinMar Racing supplied the precision radial and thrust bearings that are critical to carrying the loads generated by the top hat without compromising wing rotation.
SEAHORSE 45
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