Motor Boat & Yachting – May 2018

There are over 100 layers of carbon-
fibre weave in their construction and
they are infused with resin before
being oven-cured. SEAir also has the
use of a five-axis robot that can make
two foils in three days using prepreg
carbon-fibre strands. Prepreg, as the
name implies, is carbon-fibre matting
that has been pre-impregnated with
a resin, often epoxy, so that it is ready
to lay straight into the mould. This
process is faster but more expensive.
One of SEAir’s major obstacles is
producing the foils to an incredibly
high standard yet ensuring they
remain affordable enough to appeal
to the mass market. A tough brief.
The foils, which weigh only 17kg
each and are incredibly strong, are
then slotted through the hull into a
reinforced composite box and held in
place using a pair of Dyneema cords
and the sheer force of water pressure.
Such is their inherent rigidity, two
fully grown adults could stand on
a deployed foil and it wouldn’t budge
an inch. Given the extreme forces
coursing through these ornate
structures as the RIB glides out of
the water, it’s a comforting thought.

The engine is a standard 115hp

Yamaha outboard, though it is the

long shaft version, and it’s fitted with

a pair of extended fins to increase the

amount of lift produced at the stern.

There is a smaller plate fitted about

halfway up the outboard shaft to

deflect spray from the propeller, as

it rotates at a shallower depth than

usual. The yard believes the standard

115hp outboard that comes with

a Zodiac 5.5m is overpowered for

the more efficient foiling version so

the 100hp or even 90hp alternative

would be a better match. “It is key,”

says Forest, “that the foils integrate

seamlessly with how the boat

operates and do not detract from

the original product or alter the way

the boat has to be used in any way.”

THE MILLION-DOLLAR QUESTION

We’ve heard the back story and seen

how the hydrofoils are made but

most importantly, do they work?

Lorient’s harbour is renowned

for its protection from the moody

Atlantic, but days of squalls ensure

that there is some fierce residual

swell to have a play in outside the

protection of the port.

The SEAir RIB is rafted alongside

a standard 5.5m Zodiac with the

same engine, which will act as a

chase boat and handy back-to-back

comparison with its foiling cousin.

To look at it, you would have no idea

that the SEAir is any different to the

standard RIB, especially as the murky

water means you can’t see the foils.

The only clue is a trio of rocker

switches on the dashboard that raise

and lower the foils and control their

angle of rake. I stand in front of the

helm, clip on the kill cord and take

hold of the wheel and standard

Yamaha throttle – so far, so normal.

Even though the foils can be

lowered and retracted in 20 seconds,

I leave the berth with them deployed

to see if the sensation is any different

to normal. It isn’t. There’s no

sensation of the appendages jutting

down below the waterline and the

boat behaves at slow speed just as it

would normally.

On this prototype version, the rake

of the foils has to be set before you

increase the speed as the actuators

aren’t beefy enough to do it on the

move. We begin with the rake set to

zero, which optimises the angle of

attack for a cruising speed of 20-25

knots in calm conditions. The pitch

of the outboard is important in this

process and the trim is set at 60%

(100% is the outboard tilted fully up)

to get us started. The foils begin to

work at around 15 knots but aside

from the bow rising noticeably (but

not alarmingly) higher than normal,

it doesn’t feel all that different to

easing on to the plane on a regular

hull. By 20 knots, the foils are in full

effect and we are gliding over the

surface of the water with the forward

sections of the hull gently brushing

COMPARISON BETWEEN SEAIR'S FOILING RIB

AND A STANDARD ZODIAC 5.5M

Speed Fuel burn

RPM SEAir Zodiac Increase SEAir Zodiac Decrease

1,000 3.6kt 3.7kt -2.7% 2.0lph 2.4 lph -16.7%

1,500 5.1kt 4.9kt 4.1% 3.3lph 3.6 lph -8.3%

2,000 6.4kt 5.8kt 10.3% 5.4lph 5.3 lph 1.9%

2,500 9.5kt 6.7kt 41.8% 7.2lph 8.5 lph -15.3%

3,000 16.2kt 10.0kt 62.0% 9.2lph 10.9 lph -15.6%

3,500 18.6kt 18.0kt 3.3% 10.0lph 14.0 lph -28.6%

4,000 23.3kt 20.8kt 12.0% 14.5lph 16.1 lph -9.9%

4,500 27.6kt 24.1kt 14.5% 17.3lph 20.4 lph -15.2%

5,000 29.7kt 27.0kt 10.0% 25.6lph 26.8 lph -4.5%

5,500 32.5kt 32.0kt 1.6% 34.2lph 35.2 lph -2.8%

6,000 36.5kt 34.0kt 7.4% 40.6lph 40.0 lph 1.5%

The angle of attack can

be adjusted to suit the

speed and conditions

The foils can be

raised or lowered

through the hull

When retracted,

they tuck around

the RIB’s tubes

Each carbon-fi bre foil

weighs a mere 17kg

BOAT MASTER NEWTECH