Rafale II’s first major outing at the U.S. Foiling Week event in Miami (Courtesy of ETS and Martina Orsini)
The first ETS Rafale project started in early 2014 with a relatively small budget of only $100,000 USD, considerably less than established rival C-Class teams.
However, the students benefited from the considerable support and technical advice provided from over 40 project sponsors. This included the Canadian composite materials producer Scott Bader North America (then Scott Bader ATC), which became a key sponsor for both Rafale I and II, providing a variety of high-performance composite resin, tooling and structural adhesive products, as well as technical support. This second ETS team is building on key learnings from the Rafale I team, which made history by being the first ever student team to compete in the highly-competitive and technical International C-Class Catamaran Championship (ICCCC) racing sailing competition, nicknamed the “Little America’s Cup” or “Little Cup”. The event gained this nickname because, for many years, C-Class catamaran builders have been at the forefront of composite technology and design, having influenced both the creation of the World Speed Sailing Committee and modern racing yacht designs including the America’s Cup class AC72, AC45 (wingsail design) and AC50 racing catamarans.
How it’s made:
1 – FEM of the new carbon fibre/epoxy hull design
During the design and production stages of Rafale I and II, in addition to the sponsors, the ETS students tackled a number of project challenges with expert support and technical advice provided by three key people affiliated to or working within the ETS Engineering faculty. Professor Simon Joncas, a lecturer and research academic in the ETS Automated Production Engineering Department with a Ph.D in composite structures, is the team’s mentor and provides much of the technical guidance about component design and the new manufacturing processes used by the Rafale II project team in the ETS engineering department facilities. Julien Chaussée, a qualified aerospace engineer and former member of the British “Invictus” C-Class catamaran team, advised the team on FEM modelling and beam optimization. Xavier Grossmann, who has an MSc. in mechanical engineering, is a design engineering conception consultant.
FEM of new CF epoxy hull design anaysis
The key issue for Rafale I was that, although the originally designed carbon fibre composite laminate used for the hulls was extremely strong, achieving an ultimate tensile strength (UTS) of 1800 kg/cm² (176.5 MPa) in laboratory tests, it proved to be too heavy for this extreme level of competitive racing. To reduce weight, the hull had to be totally redesigned using FEA and CAD technology based around a carbon fibre/epoxy prepreg system for the new hull laminate.
2 – Hull mould layup and curing
The new carbon fibre/epoxy prepreg hull half sections for Rafale II were moulded by low-pressure vacuum bagging out of autoclave (OoA) using heated tooling with a mould dwell temperature of 93°C for ten hours.
Fabrication des moules de coques
Heating wires arranged on the outer surface of the female hull mold.
Finished heated hull mould with Crestomer 1152PA in the corners
3 – Hull layup and curing
Layup of the carbon fibre/epoxy prepreg hull half sections of the Rafale II.
Carbon fibre/epoxy prepreg layup
Laser placement & Low-pressure vacuum bagging out of autoclave (OoA)
4 – Assembly of Rafale II new carbon fibre/epoxy hull-halves
To minimise weight, the two halves of the hull were then bonded together using Scott Bader’s Crestabond M1-30 structural adhesive in the second stage assembly process, as were the new carbon fibre cross beam sections; the beams were fabricated by ply winding onto extruded aluminium profiles using the same epoxy prepreg grade specified for the hulls.
The new L-shaped daggerboards and T-shaped rudder foil skins were moulded in the same way as the hull in two half sections using a carbon fibre/epoxy prepreg, and then assembled around 3D-printed cores using a structural adhesive. The assembly of the 7.62m long hull sections proved to be a real challenge for the ETS team, being the first time the students had bonded composites parts on such a large scale with no other fixings being used.
Crestabond M1-30 was selected by the ETS team as the most suitable structural adhesive to bond the new epoxy/carbon fibre hulls and cross beams due to a combination of its performance capabilities in use with no need for any mechanical fastenings, along with its processing characteristics, which enabled easier and quicker assembly by the team of six students compared to other adhesives trialled. This adhesive is a toughened, two-component 10:1 primer-less acrylic adhesive developed in-house by Scott Bader for structurally bonding composites, thermoplastics and metals, designed to meet the bonding requirements of most assembly operations.
Close up – Assembly of Rafale II new carbon fibre/epoxy hull halves bonded with Crestabond M1-30
Given the extreme performance conditions that a C-Class hull has to cope with, to ensure maximum adhesion strength, the epoxy laminate bond surfaces were first sanded with 220 grade paper and then cleaned with acetone. Being a primer-less adhesive, Crestabond products require only minimal surface cleaning of the substrates being bonded. Crestabond M1-30 was applied from 400ml coaxial cartridges using manual hand guns under 20°C ambient conditions, which provided a 40 minute working time and a fixture time of around 85 minutes.
According to published technical information, this structural adhesive has excellent impact, peel, shear and compressive strength, and fatigue resistance properties. Typical material property values (tested to ASTM D638) of 17-20 MPa for tensile strength, 750-1000 MPa for tensile modulus and an elongation of >100% are quoted in Scott Bader’s technical data sheet. Crestabond M1-30 was approved by DNV-GL as a “duromeric” adhesive suitable for use in the joining of components for marine applications, passing test criteria which satisfied DNV-GL of its performance capabilities for structural bonding applications in FRP boatbuilding within stipulated operational limits and for specific substrates, namely aluminium, glass fibre-reinforced polyester resins, and glass fibre-reinforced epoxy resins.
Assembled new carbon fibre/epoxy hull for Rafale II
The adhesive is also currently being trialled to structurally bond the new epoxy/carbon hydrofoil half sections, following some tolerance and adhesion issues with an epoxy prepreg adhesive that was used to assemble the first set of T rudders and L-foils; once again no fastenings are used in the design.
The MDF plugs for the new hulls and rudders were manufactured externally by two specialist toolmaking companies and then finished by the ETS students, who made all the individual moulds. The Poly-Fair F24VE vinyl ester resin fairing compound was used in the heated moulds for the new hull sections to cover the wire elements prior to the second mould tool infusion.
Unusually, Scott Bader’s Crestomer 1152PA urethane acrylate-based structural adhesive was also used in both the hull and the rudder and daggerboards moulds, primarily to eliminate sharp-edged stress areas, especially in the thin foils, and to prevent any dry areas or air inclusions in the corners during infusion. The curved radius corners also helped with fibre alignment and avoided any gelcoat displacement when the vacuum was applied during the infusion stage.
The students additionally found that using Crestomer 1152PA in the corners not only avoided stress concentration points in the finished parts, but being such a very tough, flexible product, had the added benefit of producing a more durable mould tool that was far less prone to corner damage during part demoulding.
The origins of the C-Class date back to the early 60’s, born out of a disagreement between Great Britain and America as to which country produced the fastest catamaran. The first International Catamaran Challenge Trophy (ICCT) took place in 1961 and continued up until 1996. After a resurgence of interest in 2004 in C-Class catamaran racing, the successor ICCCC event has attracted some of the best racing catamaran designers, boatbuilders and sailors in the world. There are now a number of foiling race events around the world for different sailboat classes.
The C-Class is a recognised “development racing class” double-handed, double-trapeze foiling catamaran with three key maximum measurement limits: 7.62m long, 4.26m beam, with a 27.87m² sail area. Built for pure speed, these superlight catamarans, weighing no more than 220kg, have been referred to by some sailing experts as “the world’s most efficient sailing machines”, being notoriously difficult to sail well but able to achieve over three times the actual wind speed. With an experienced crew in the right sailing conditions, C-Class catamarans have reached hydrofoiling speeds over the water of up to 34 knots (~63 kph).
5 – Manufacturing of Rafale wingsail
A C-Class catamaran literally “flies” over the water on the twin hydrofoil J-shaped daggers, mounted one in each hull, along with linked T-shaped hydrofoiling rudders. However, the real design difference in modern C–Class boats is the way the wind power is harnessed, drawing on wing designs from both aeronautical engineering and evolved bird wings found in nature. Unlike a typical sailing boat, a modern C-Class catamaran does not have conventional sails, being powered instead by a rigid, symmetrical wingsail, typically made from lightweight, high-performance composite materials.
The wingsail design developed for Rafale I that is currently being used on Rafale II has distinct sections that perform differently. The front section of the wingsail is rigid with an aerodynamic carbon fibre-reinforced U-shaped leading-edge section.
To provide better aerodynamics and more speed, the ETS wingsail design includes a “morphing” trailing edge in the lower section of the rear part of the wing as well as the movable flap upper rear section. This morphing trailing edge section of the wing continuously changes shape and flexes in response to the applied wind force, curving slightly in a similar way to a flapping bird’s wing, which results in an increased forward thrust. Design optimization of morphing wing aeronautical designs is a globally established research field, with ongoing projects investigating the design of next-generation morphing aircraft with improved flight performance.
The original Rafale I symmetric “morphing” wingsail under construction
As well as the structural adhesive, the carbon fibre-compatible Crestapol high-performance urethane acrylate-based resin was used extensively to manufacture key structural parts for the massive 28m² wingsail. The leading and trailing edges, flap spars, wing foil box fairings and bulkhead panels were all vacuum infused using Crestapol 1250LV. The rigid bulkheads were assembled with Crestabond M1-05 and M7-05 structural adhesives, which were also used for bonding a variety of FRP and metal parts on the wingsail. The 9.75m central carbon fibre mast, 120mm in diameter and weighing just 16kg, is the primary structural element for the wingsail, which when fully assembled provides a 13m sail height. The mast is conventionally supported by steel wire stays.
The final part
Rafale II in action on the water during the 2018 US Foiling Week regatta
Hydrofoiling close up