Kelly Slater’s equipment is a perennial topic of interest. But when Strider Wasilewski checked out Slater’s backup boards during the Pipe Masters yesterday, he spied something surprising even for the forward-thinking Champ: a set of whale bump thruster fins. A set of what-now, you ask?
Strider’s equipment check left some questions unanswered, so we dug into the matter. Whale bump fins are a seldom seen fin design distinguished by having a ridged leading edge. From the side, the leading edge has a series of uniform ripples, called tubercules, kind of like a Ruffles potato chip. Aside from the whale bumps, Slater’s fins appeared to have about the same plan shape as a fairly standard set of thruster fins.
Whence the concept of these fins? Ask a humpback whale, whose flippers are the inspiration. The tubercules create lift and flow, and the hulking mammals can thank them for their unexpected agility.
As one source puts it: “Whereas sheets of water flowing over smooth flippers break up into myriad turbulent vortices as they cross the flipper, sheets of water passing between a humpback’s tubercles maintain even channels of fast-moving water, allowing humpbacks to keep their ‘grip’ on the water at sharper angles and turn tighter corners, even at low speeds.”
The same design has even been used on wind turbine blades. “When the angle of attack of a whale flipper–or an airplane wing–becomes too steep, the result is something called stall,” according to an MIT Technology Review write-up about a Harvard study of whale bump turbine blades. “Experiments have shown, however, that the angle of attack of a humpback-whale flipper can be up to 40 percent steeper than that of a smooth flipper before stall occurs.”
Another person you could ask is Roy Stuart, the Kiwi surfboard shaper and giver of zero fucks. In YouTube videos he holds forth from a seat he calls the “moaning chair” with apparent expertise about numerous aspects of surfboard physics. Stuart says the whale bumps allow for a steeper-than-usual angle of attack and enhance flow. If you want a pair, Stuart sells 3D printed whale bump fins.
He can explain the physics better than us, so take it from him:
