Professional BoatBuilder - April-May 2018

April/MAy 2018 23

speeds as modest as 6 knots.

On the control-system side,

faster, smaller, and cheaper

computers further improved

performance.

Modern hydrofoils also

owe a lot to the designers and

engineers who developed

those light hulls and effective

foil sections and shapes (i.e.,

for boats that have very lim-

ited power to get foilborne),

using computer-aided design

(CAD) software like Rhino

and programs for finite ele-

ment analysis (FEA) and com-

putational fluid dynamics

(CFD) that allow for more

accurate modeling and perfor-

mance predictions. Advanced produc-

tion methods that rely on 5-axis com-

puter numerical control (CNC) routing

machines and 3D printing of molds

and parts also help produce those state-

of-the art hulls and appendages. 

Surface-piercing foils were standard

for decades, because they were rela-

tively easy to build, offered inherent

height control—as lift reduced when a

boat rose farther from the water—and

provided lateral stability with a broad

foil span that extended beyond the

hull. Now, computers that work reli-

ably in a marine environment coupled

to sensors and hydraulic controls

make it possible to fly a boat on fully

submerged foils of an inverted T-shape

that extend beneath the surface to

where the water is less disturbed.

Small sailing dinghies like the Moth

or Dave Clark’s UFO (see “The Peo-

ple’s Foiler,” Professional BoatBuilder

No. 166) are good examples of T-foil

applications.

into developing foilborne warships.

While the idea of foiling frigates

never played out as envisaged, the

research and testing yielded troves of

data and knowledge that remain rel-

evant today as boat designers and

builders strive to bring foiling boats

into the mainstream.

Early foiling craft were compara-

tively heavy brutes built from alumi-

num, with steel foils. Their designers

quickly ran up against the horsepower

requirements to fly these already heavy

vessels, adding weight that called for

even more horsepower. Advances in

construction techniques, composite

materials, and propulsion technologies

solved some of these problems. Resin-

infused carbon fiber cured in an auto-

clave oven for minimum weight and

maximum strength changed the power-

to-weight equation remarkably. Lighter

boats need less power and become

foilborne much quicker. Today, even

pedal-powered craft can lift off at

foils in the water and hulls in

the air? Is foiling “a solution

looking for a problem,” as

someone quipped, or is there

a “killer app” on the horizon

that will turn foiling power-

boats into a common sight? 

Foil evolution

Let’s revisit some of the

intriguing benefits foiling

offers. For one, it avoids the

bumps we know from hull-

borne boats. It also drasti-

cally reduces drag, which

means the boat can go faster

and/or farther on less power.

Ideally, this translates into

fuel savings (because hydro-

foils have a much bigger lift/drag ratio

than planing craft) and lower emis-

sions of carbon dioxide and nitrous

oxide, two contributors to climate

change and respiratory diseases. And

as Talaria showed, foilborne operation

virtually eliminates wake, which helps

sensitive ecosystems and creaky infra-

structure along waterfronts. But there’s

one huge challenge: balancing those

benefits against the cost of building

exotic one-off boats fitted with com-

plex foil-control systems.

While the technology has been the

subject of a lot of press lately about

myriad high-tech foiling sailboats (i.e.,

the Moth dinghy, numerous multi-

hulls including the America’s C u p

catamarans and Open 60 keelboats in

the Vendée Globe), the underlying

princi ples have been well understood

for a long time. Powered hydrofoils

have been around for more than a

century, and during the Cold War,

militaries poured time and money

Advances in foil design, construction materials,

and networked ride controls have

led to a renaissance in hydrofoiling.

Dieter Loibner

Having worked on cutting-edge America’s Cup designs, Paul

Bieker of Bieker Boats in Seattle, Washington, also applies

his knowledge of efficient foil design to smaller craft.

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