Carbon fiber rudders, dagger board hydrofoils prove their mettle

CarbonicBoats designed and manufactured carbon fiber/epoxy dagger board and rudder hydrofoils as retrofits for several International A Division Catamarans that recently competed in the 2014 world championship races in New Zealand.

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GMS Composites (Victoria, Australia) reports that its GMS EP-270 epoxy prepreg system was used by CarbonicBoats (Rose Bay North, Australia) to manufacture carbon fiber composite dagger board and rudder hydrofoils as retrofits for several International A Division (or A Class) Catamarans that recently competed in the 2014 world championship races in New Zealand at Takapuna, North Auckland.

Boats retrofitted with these latest design L carbon fibre epoxy rudders with lifting and stabilizing foils came 1st, 2nd, 3rd and 5th in the International A division. The novel, Paradox branded composite rudders are referred to by CarbonicBoats as heave-stable L foils. Each of the carbon fiber/epoxy foils in the set was low-temperature molded using GMS Composites' GMS EP-270 epoxy prepreg system.

Competitive racing vessel designs must strictly comply with the international development A class rules, which limit boat dimension to: length 5.5m (18 ft), beam 2.3m (7.5 ft) and a sail area 13.9m2 (149.6 ft2). Rigging and all appendages must also comply with race rules. Boats typically have a carbon fiber mast with a height of 9m (29.5 ft), with the two hulls constructed from a carbon/aramid honeycomb sandwich epoxy laminate. The overall weight of a finished, rigged catamaran, ready to race, is 75 kg (165 lb). The engineering challenge is to achieve the greatest possible stiffness for the given weight. For CarbonicBoats the design aim was clear: To provide a commercially viable retrofit upgrade package to convert existing A Class racing catamarans to stable foiling, providing skimming flight with minimized drag when in foil-assisted mode, without major structural modifications.

The new Paradox L/V foil designs are the result of more than 12 months of intensive modelling, simulation and prototype testing, which included trials under real race conditions on prototype test platforms. In Youth division and Grand Masters A class meets, catamarans fitted with prototype foil sets achieved 3rd place in both races.

The CarbonicBoats design team has taken a different approach from existing C, S and J shaped foil designs, to address the balance between stability, side force, vertical lift and minimal drag, and for the rudder design obtaining higher heave values for optimised steerage control. There are two differently shaped designs for the two pairs of carbon fiber/epoxy prepreg parts that make up the new design Paradox A Class catamaran foil set: two polyhedral-shaped retractable dagger board foils, one on each hull; plus L-shaped rudders mounted on the transom of each hull, linked together to a central helm. The engineering demands on each of the hydro foil parts are extreme. Like an aircraft wing tip, each of the carbon fiber/epoxy prepreg parts must maintain a level of stiffness, but also be able to have the flexural properties needed to allow for the degree of foil curvature at high speeds; the two lower sections of the dagger board foil can bend in excess of 90° and then must fully recover; the dagger foil shape varies depending on the boat speed, trim and point of sail taken during a race.

Dario Valenza, founder of CarbonicBoats, explains: “For our L/V foils, stiffness, accuracy, dimensional stability, reliable consistency in performance properties and a very high quality surface finish are all very important. Using GMS EP-270, we can fabricate foils 2 percent thinner than competitive foil designs, with a trailing edge thicknesses sub 1 mm. This is only possible with a good stable resin matrix. GMS prepregs allow us to accurately replicate the specified design characteristics with no needed to compromise, and finished parts remain stable in use.”

Valenza adds: “GMS prepregs have good tack, so they can be easily positioned and worked into curves for efficient mold, with a relatively short recommended cure time of only 60 minutes at our preferred 110°C mold temperature, with the ramp up and dwell times overall being shorter than the previous low-temperature epoxy system used.”