When we started off down this road in mid-2016, the world had already gone foil- crazy: curved boards or straight, L- or J-profile, tips or no tips, and the full range of development and designs. A lot was already known about the performance of the various options, and most of that knowledge is held by our design partners VPLP. We mined all of their extensive experience to come up with the solution for the Gunboat 68 that found the perfect balance of performance, stability, and ease of use.
“We ran a whole range of board concepts,” says Vincent Lauriot-Prévost, the ‘LP’ of VPLP. “While we remained focused on modeling side force and vertical lift, and we also factored in the practical parameters of the brief such as reliability, interference with the interior, the simplicity of maneuvers and the versatility of cruising and racing versions. All the candidates we tested came from either ORMA trimarans, foiling and non-foiling IMOCA monohulls and the past three America’s Cup multihull editions. Ultimately it was about finding the right formula for this program.”
All in all we did fourteen iterations of board VPPs, running them with different displacements, rig heights, symmetric and asymmetric boards – every variable there is! We also checked true wind hull fly speeds to stick to our safety targets: the performance-rigged Gunboat 68 shouldn’t fly a hull below 16 knots TWS, or 20kts for the cruising version. To be clear, our world-cruising and regatta-worthy Gunboat 68 is not a fully foiling, flying catamaran – we’re talking about the ability to push for performance and fly a hull, which she is structurally capable to do.
Without flying the platform, boards with foils or tips could not only generate lift, reducing wetted surface area and therefore drag, but could also help to improve comfort and stabilize the platform by preventing ‘heaving’ (sudden vertical movement when sailing through waves). We wanted to explore the options.
First we looked at curved boards. They create lift and have the added bonus of matching the curved profile of the outside hull, making the board cases less intrusive to the living space below. VPLP ran a VPP study on a variety of curved boards with and without tips. They all showed that curved boards bring the center of lift inboard, actually reducing righting moment, which will make a hull fly earlier. Safety is a cornerstone of the Gunboat philosophy though, so much so that we increased the beam of the Gunboat 68, and therefore the righting moment, to make her a safer boat. Further, the build complications of curved molds added more complexity for very little gain. We opted against curved boards.