Tech Talk: Rudder Nodules
Rambler 88 under sail in moderate conditions
One of the ‘nobby’ rudders exposed during the boat’s christening
One of the coolest new builds to emerge from a boat shed in years is Rambler 88, a Juan Kouyoumdjian-designed all-out monohull monster that was completed by New England Boatworks, in Portsmouth, Rhode Island, this past winter. While Rambler 88 brims with bleeding-edge design concepts, her rudders, which carry nodules on their lower leading edges—much like those seen on humpback whales’ fins—caught our eye at SAIL, so we called the world’s foremost foil expert to find out more.
“I believe the nodules do two things, one that has been proven, one that has not,” says Paul Bieker, one of Oracle Team USA’s core designers and a principal at Bieker Boats in Seattle, which has successfully employed nodules on some designs. “The proven effect is an increase of the maximum lift angle of attack, i.e. a more gradual stall. The non-proven effect is the rotating turbulence from the tubercules creating ‘fences’ along the suction side of the foil [on boats with a single rudder], which may delay ventilation.”
Since Rambler 88 carries twin rudders, says Bieker, the primary benefit here is a boat that’s a touch more forgiving on the helm, albeit at a price. “There’s a small drag penalty at normal sailing angles of attack,” Bieker says. “For this reason, I don’t expect nodules to proliferate in grand prix sailing.” Time will tell how they serve Rambler 88.
