Inside Angle: Foiled Again

What’s new is actually quite old. Bill Prince dives into the ups and downs of hydrofoils.

We’re discussing a term in our design office today: Mustache foils. Pardon? Among the newly expanding genre of foiling powerboats, they’re hydrofoils attached to the lower units of outboard motors, shaped like Snidely Whiplash’s melodramatic handlebar mustache from the old Dudley Do-Right cartoons. Foiling powerboats, you say? Hah, hah, hah, HAAH!

Foiling boats run suspended out of the water atop hydrofoils. Hydrofoils (mustachioed and otherwise) are wings that attach to a boat’s hull, generating some drag but also lots of lift-. This lift raises the boat’s hull entirely out of the water at speed, eliminating the substantial drag caused by the hull’s wetted surface area.

Foiling powerboats are not new. Far from it. In 1905, a half-century before Whiplash began his animated antagonism of Dudley Do-Right, Italian aeronautical innovator Enrico Forlanini built the first self-propelled foiling boat. Forlanini devised a 100-hp vessel capable of over 30 knots. No word if he had a mustache, but he did this before the world had discovered stainless steel, plastic, FM radio and the ball screw, for crying out loud. The only known photo of the boat was taken by Alexander Graham-Bell, who then bought the patent.

If you have even a passing interest in sailing, you’re likely aware that the fastest sailboats fly above the water on articulating hydrofoils. Today’s racing “sailors” wear Kevlar vests and helmets to give them a chance at survival, not if—but when—they stuff their bow at 40 knots. At that moment, the boat becomes a carbon fiber trebuchet of sorts, flinging our modern-day Dennis Connor-types around the race course with abandon. It makes for good TV if you have ESPN 8, The Ocho.

And 40 knots is an everyday occurrence for these boats. In fact, the current sailing speed record holder is the 40-foot Vestas Sailrocket 2 which achieved speeds of 65.5 knots, or 75 mph, over a 1,600-foot course. Hurricane not included; the wind was blowing just 28 knots at the time.

Enough about sailboats. Let’s add some power after a century’s hiatus and see what we can do. That’s just what’s happening in the 2020s at some big production powerboat builders.

Not long ago, Groupe Beneteau (Prestige, Four Winns, Wellcraft, et al.) released video of a concept foiling powerboat that has been used to test foils under real-life conditions for possible use on future motoryachts. The foils flip out of the way, so the boat doesn’t take up additional room when docking.

Princess Yachts uses its Active Foil System on the Princess R35, a 35-footer achieving speeds of 50 knots. (The R stands for Revolution.) Two retractable T-shaped foils, each three feet long and 10 inches wide, are installed in the hull along with a pair of 430-hp Volvo-Penta V8s coupled to Duoprop sterndrives.

Looking for something smaller? The Valo Hyperfoil is a high-speed semi-autonomous electric hydrofoil personal watercraft (PWC) promising “revolutionary water mobility”. Valo claims the Hyperfoil is the first “major upgrade” to the jetski design in over fifty years. Retractable carbon fiber hydrofoils elevate the PWC above the water, promising speeds to 58 mph.

The 26-foot Candela Seven is a fully electric foiling powerboat claiming a range of 50 nautical miles at 20 knots. But the Candela Seven is a complicated machine, relying on Stealth bomber-esque technology to keep the bow pointed in the right direction as the boat balances its entire weight on a very small foiling footprint. This inherent instability can only be addressed by adjusting the flexible main foil 100 times per second via the boat’s flight computer, absorbing information from accelerometers plus gyroscopic, barometric and ultrasonic sensors that constrain roll, pitch, running attitude, speed and other factors.

Whew! I think maybe I’d just like to crack open a beer and go fishing instead.

Modern-day foiling powerboats are in their infancy, and there may be good reasons why the concept never took flight a century ago. But we have the computing power to make the theory work in practice now. Still, what if the computers fail? And how will fast foiling boats safely handle an impact with a submerged object—or animal?

Snidely Whiplash, if you’re out there, start twirling your mustache and help us figure this all out.

View the original article to see embedded media.

This article originally appeared in the April 2023 issue of Power & Motoryacht magazine.