What is foiling?
Foiling refers to the use of hydrofoils
attached to the hull of fast boats,
which provides additional lift at
planing speeds – often enough to lift
the hull completely clear of the water.What is the benefi t of this?
Efficiency. The enemy of fast boats
is the amount of effort required to
push them through the water. Planing
boats go some way to addressing this
by rising up over their own bow wave
and skimming across the surface, but
the stern sections are still immersed,
creating significant hydrodynamic
drag. It follows that if you can lift the
boat completely clear of the water,
hydrodynamic drag is only acting
on the foils themselves and the
sterngear that propels and steers it.Any advantages beyond effi ciency?
Lifting the boat clear of the surface
can reduce the disturbance of waves,
smoothing the ride, but only up to
a point. It’s not just about lift though- active foils can also be used to
improve stability or handling and in
some circumstances, can improve
efficiency even without lifting the boat.
How do foils work?
Foils work in a similar way to aircraft
wings. In simple terms, as they move
through the water they deflect the
flow, which exerts a force on the foil.
If that force is upward, the faster they
move, the greater the lift.So why are they so much smaller
than aircraft wings?
Because water is much denser than
air – almost 800 times, in fact. The
foils have far more to push against
than aircraft wings, so don’t require
the same surface area.Is this new technology?
Far from it. Foiling technology can
be traced back to 1898 when Italianinventor Enrico Forlanini began work
on a ‘ladder’ foil system, obtaining
patents in both the UK and the USA.
He had a prototype operating on
Lake Maggiore soon after. British
boat designer John Thornycroft
followed up with a series of scale
models featuring stepped hulls and
a single foil, and by 1909 had a full-
scale 22ft prototype running. During
WWII, the German military developed
a 17-tonne foiling mine layer that was
tested in the Baltic at speeds of
up to 47 knots. By the early 1950s,
the first commercial hydrofoil ferry
was running between Italy and
Switzerland and a decade later,
a private hydrofoil yacht featured
in the Bond movie Thunderball.Cup contenders started to use foil-
shaped daggerboards to hit speeds
of more than 40 knots. Ben Ainslie’s
spectacular last-gasp victory for the
Oracle USA team and his subsequent
BAR Land Rover Cup Challenger
brought foiling to a global audience.
More recently, we’ve seen the
emergence of several foiling motor
boats, including the SEAir RIB and
the Sunreef Open 40 Power. More
exciting still is the news that Princess
will use an advanced Active Foil
System on its new R Class superboat.What has changed?
Technology has overcome many of
the shortfalls of older systems. Simon
Schofield, chief technology officer at
BAR Technologies, told MBY the real
game changer has been the adoption
of ‘Dalí’ foils. Instead of two fixed
V-shape foils, Dalí foils use four
independent L-shaped blades that
stick out of the hull at an angle before
curving up like Salvador Dalí’s famous
moustache. They are far more efficient
and can be retracted, solving the
berthing and draught issues. In
addition, computer-controlled active
systems allow the foils to be adjusted
to suit speed and sea conditions.
This doesn’t just improve efficiency,
it can enhance the ride and handling
too. When cornering, for example, a
traditional hydrofoil boat doesn’t lean
into the turn, making it uncomfortable
for passengers. An active system can
adjust each foil to induce the correct
degree of lean. Modern materials also
reduce drag and cavitation.How about propulsion?
The Enata Foiler uses twin BMW diesel
320hp engines, but instead of being
connected to the propellers with hefty
drag-inducing shafts and gearboxes,
these generate electric power which
can be sent down a thin flexible cable
to slender electric motors mounted
on the retractable rear foils.Foiling technology
The truth about
Fitting foils to powerboats is all the rage, but how do they work and why are they back in fashion?
Technology has overcome many
of the shortfalls of older systemsMBYINVESTIGATES
The latest generation of
curved foils are dubbed
‘Dalí’ foils after the artist’s
famous curled moustacheWhy did they never catch on in
production boating?
Traditionally, high-speed hydrofoils
used large V-shaped foils that jutted
out beyond the boat’s beam. This
made berthing tricky and increased
the draught. They were also costly to
construct, vulnerable to damage and
difficult to power, as the propellers
of conventional shaftdrives would
be clear of the water once foiling.
Lastly, although hydrofoils were often
more efficient than monohulls, high-
speed cats could usually match the
efficiency without the drawbacks.Why are they back in the news?
Foiling technology came back into
public focus when the 2013 America’sNEWS