Chris Mitchell is a man with vision – and a fleet of dinghies ... - Ingenia

INNOVATION
The first Access Dinghy prototype on its maiden sail at Sandringham, seen sailing downwind under asymmetric spinnaker © Access Dinghy
UNIVERSAL
DINGHIES
Chris Mitchell is a man with vision – and a fleet of dinghies to prove it. He has helped
hundreds of disabled people discover the freedom of sailing, through his Access Dinghy
Foundation. Sally Wilkes found out more about his new prize-winning skiff that will
power sailors all the way to the 2008 Paralympics in Beijing.
ISSUE 27 JUNE 2006
31

INNOVATION
Bethwaite, this type of boat
design does not subscribe to
neat equations. He fine-tuned
the hull by towing the SKUD18
hull behind a speedboat and
plotting drag curves, ensuring
the design parameters such as
keel weight, draft (keel depth in
the water) and uncrewed mass
displacement were maintained.
The final design has low drag,
meaning the boat heels fairly
easily but gives a faster ride.
carbon fibre bowsprit, completes
the sail tally, taking the boat
above a speedy twelve knots.
An asymmetric, rather than
standard, spinnaker is particularly
effective on fast planing skiffs
like the SKUD18 because they
are fast enough to generate an
increase in apparent wind when
reaching (sailing across the
wind), so it is often faster to zig
zag to the bottom mark rather
than sailing directly downwind.
The SKUD18 with its double rudder and bulb keel configuration on clear display © Access Dinghy
The SKUD18 (SKiff Universal
Design) was selected on
7 November 2005, by the
International Association of
Disabled Sailing (IFDS), as the
Paralympic vessel of choice in
the two-person keelboat
event. It then quickly snapped
up its first accolade: the
Australian Sports Innovation
Award in February this year.
The vessel is the latest and
snappiest in the stable of Access
Dinghy sailboats but, as Mitchell
points out, it is not a disabled
sailing boat per se. Rather, he is
creating a universal craft that can
be adapted for virtually anyone
to sail, regardless of skill or
physical prowess. “We take the
most difficult and complicated
cases and get them sailing, and
the others just fall along in line.”
SKIFFS FOR ALL
Admittedly the SKUD18 will take
a little more taming than the
Liberty; the Access Dinghy club
boat design that the SKUD took
inspiration from. At 5.8m long,
this lead-assisted skiff (a type of
dinghy) has an asymmetrical
spinnaker and hi-tech rig making
it the ‘turbo’ class specialised
version designed for top-level
performance and excitement –
with a crisp response that is
equally challenging for both
able-bodied and disabled sailors.
But while the skiff is high on
thrills, spills must be contained –
the Paralympic competition will
be a strict one-design class to
create equity for all competitors,
with two sailors seated (and in
most cases, strapped in) on the
centreline. The addition of a
spinnaker sail means the boat
could get knocked down, so selfrighting
and self-draining
features are vital. The SKUD18
had to be designed for the
worst-case tip scenario – a
ventilated tetraplegic who
can only move their tongue –
making it imperative that all
seats are clear of the water when
the boat is on its side. Other
design configurations allow at
least one person to move
around the boat, so edge seats
also need to be kept out of the
water during heeling (where the
boat leans over). This
combination of spinnaker and
central seating is an innovation
in this class.
CONCEPT AND DESIGN
The SKUD18 concept came to
life two years ago and has
involved collaboration with
renowned Australian skiff
designer Julian Bethwaite (who
designed the Olympic class 49er
skiff ), and naval architect Martin
Billoch to bring it to this stage.
From the beginning Mitchell
knew he was going for a faster
planing hull, rather than the
more stable displacement hull
of his earlier models.
The final hull design is an
8mm PVC foam sandwich with
bi-directional glass and polyester
resin; a cheap and lightweight
combination. The boat’s
buoyancy chamber contains
500 litres of foam, forcing the
skiff to remain upright with more
than 100mm freeboard (the
height of the boat that is above
the water) when sailing with
the buoyancy chamber totally
flooded and the cockpit filled.
SKIFF STABILITY
A wildly heeling dinghy
needs a serious underwater
counterweight, and this is
provided by a bulb keel with
150kg of lead working as a
righting device. Two oversized
rudders also mean control is
maintained during heeling,
allowing the boat to heel to
45 degrees comfortably.
Directional stability is also
maintained by a large jib sail,
which loads the bow up in
powerful winds, keeping the
boat on course and balancing
the helm. Mitchell admits this
feature was discovered by
serendipity when trialling the
Liberty, and was subsequently
incorporated into the SKUD18.
According to Mitchell,
experiencing a wild heel is
rather unnerving at first for a
strapped-in sailor, but the
helmsman has good visibility,
since the stern rises in the air as
the boat heels, and transparent
Mylar sails give a good all-round
view. The high boom removes
the threat of being hit on the
head – the scourge of small
dinghy sailing when going about!
Testing of the hull stability and
performance enhancement was
achieved through a mixture of
experience, engineering, and trial
and error, scaling down the
ratios and lines of Bethwaite’s
79er skiff. According to
THE RIG
In technical terms, the boat has a
sloop rig (this refers to the sail
arrangement, including the mast,
sails and ropes) with high roach,
which, loosely, is the mainsail
radius and an indicator of the
boat’s speed capability. The rig’s
auto de-powering function is a
safety measure often used in
boats of this class. By encouraging
the top of the mast to flex, air is
allowed to spill out of the sails at
very high speeds in an attempt
to avoid excessive heeling. The
mainsail is fully battened
(battens extend horizontally
across the mainsail) for optimum
performance and a self-tacking
jib eases handling. The ‘boost
function’, a tube-launched
asymmetric spinnaker on a
ENABLING CONTROLS
To put the challenge of
designing for this demanding
group of sailors into perspective,
Mitchell classes someone
with cerebral palsy as: “among
the hardest to get sailing
competitively… because they
have spasms in their hands and
limbs, and can have difficulty
getting their hands and fingers
to follow instructions from the
brain. They may also have
communication problems on
crewed boats as speech can
be impaired.”
Mitchell’s team has a vast
tool kit of innovative electronic
servo-assist controls and
winches at its disposal, to help
disabled sailors make use of their
strongest or most useful body
part to control the boat.
A standard joystick controller. Access Dinghy make these controllers for fore and aft
mounting on the arm rests – left or right handed – with a variety of options using
any combination of toggle switches, push buttons, reed switches etc © Access Dinghy
“Another person we got sailing could only
move their tongue against their cheek, so we
fixed a strip with pressure switches across the
face to give three points of activation at each
station. They could control the lot with that.”
A two-straw sip and puff Liberty controller with a magnetic reed switch which
disengages and engages the jib sheet winch. The controller is mounted centrally
on a bridge. In the background are thoracic supports bolted to the backrest
© Access Dinghy
32
INGENIA
ISSUE 27 JUNE 2006 13 33

UNIVERSAL DINGHIES
INNOVATION
Generally, the most physically
disabled sailor would take the
helm at the rear of the boat and
use a manual or servo-assisted
joystick to drive the rudders,
while the second person –
someone with arm strength –
would control the sails. It would
be possible to have a severely
disabled crew controlling the
whole boat using rope handline
functions, or for just one person
to use a four-way joystick for
steering and pulling in the
sheets. As both sailors sit on
the centreline in the Paralympic
setup, traditional boundaries
between helm and crew are
blurred and both sailors could
operate any of the controls.
Servo-assist controls and
winches can control the helm
(with a variable speed option)
and the rig. Manual controls
include joystick or push/pull
Amethyst (Ame) was born with Phocoamelia. This is a condition that manifests itself
by the absence of limbs. Ame is sitting in a custom made seat fitted into her Access
2.3 single seater dinghy. She has one short foot with three toes with which she
controls the boat © Access Dinghy
lines, a cleat console for easy sail
control, and a single speed
sheet-type winch for easy
handling of other rig functions
and the keel. The servo
controller range includes a
variety of electronic joysticks and
secondary control switches. Sip
and puff controllers could be
incorporated, but in practice
they are not widely used.
The servo winches on all
Access Dinghy sailboats are
powered by worm drive
permanent magnet DC motors,
typically used for windscreen
wipers but marinised to give a
high IP53 corrosion resistance
rating. The winches use a glass
bead coated friction drum and
can pull tension in both
directions, so a single winch can
trim both port and starboard
sheets. Likewise, a single winch
can raise and lower the
spinnaker by hauling on the
halyard (rope) attached to the
head of the sail.
MULTI-FACETED
Mitchell has spent years working
with disabled would-be sailors
to come up with creative
solutions for boat control. For
example, a joystick can be
operated with any body part,
such as the hand, chin or
tongue. The operating load
would simply be reduced to
accommodate the tongue.
“Another person we got sailing
could only move their tongue
against their cheek, so we fixed
a strip with pressure switches
across the face to give three
points of activation at each
station. They could control the
lot with that,” explains Mitchell.
Another configuration uses a
magnet attached to the cheek
to operate reed switches.
Access Dinghy are able to
incorporate their own electronic
systems into the SKUD18,
including a 32 channel wireless
transmitter that can operate
16 winches. This means that, for
extremely disabled or novice
sailors, a person with a controller
can remain on shore and
effectively override the boat’s
controls should a problem occur
– rather like a remote-controlled
model yacht. However, Mitchell
aims to keep the electronic side
as simple as possible, in order
to keep costs down and avoid
malfunctioning.
Those with sensory as well as
physical disabilities can also sail
the SKUD18, though they would
be more limited by the weather
conditions. Blind sailors can
orientate themselves using a
talking compass that beeps
according to the optimum angle
to the wind, and can communicate
with a shore-based guide via a
radio link. An established system
of insignias and verbal
communication between
competing boats also exists in
blind dinghy racing.
FUNCTIONALITY
AND FEEDBACK
The boat’s functionality lies as
much in what it cannot do as
what it can, creating equity
between sailors of different
physical capabilities. For
example, an able-bodied dinghy
sailor normally uses a manual
rudder to alter the course of the
boat, and makes constant (and
often subconscious) microadjustments
to the tiller to
account for changes in direction,
swell and wind sensed through
the tiller. The SKUD18 does not
allow this. “You can’t incorporate
sensitivity of this kind into a
joystick or it would disadvantage
someone like a tetraplegic who
may have no feeling in their
hands, but has a small degree of
movement,” says Mitchell, who
argues that it should be against
class rules to allow steering that
is too light.
FULL SERVO FUTURE
Mitchell is passionate about
widening the acceptance of full
servo sailing. “There’s nothing
disabled about using a joystick,”
is an oft-heard mantra. This
may sound obvious given the
joystick’s ubiquity among
computer gamers, fighter jet
pilots and motor boat pilots, but
it is quite a leap of faith for
experienced small boat sailors to
hand over their manual controls
to servo controllers in what is
such a fast-reaction sport.
Mitchell would love to see
disabled and able-bodied
people competing in clubs
across the world using his boats.
“That is our goal: for people
sailing full servo to out-sail the
able bodied who are sailing
manually, and get disabled
people joining in everyday
events rather than having special
classes.” Future technical
developments include the
possibility of a power-assisted
swing seat that allows a disabled
person to shift their weight
during heeling. Mitchell is also
working to extend accessible
sailing to poorer countries
around the world.
Further information:
Access Dinghy Sailing Systems was supported in its development
of the SKUD18 with an innovation grant from the Australian
Government, through its business unit AusIndustry. For further
information on the SKUD18, and Access Dinghy’s other vessels,
see www.accessdinghy.org and www.bethwaite.com
BIOGRAPHY – SALLY WILKES
Sally Wilkes is a freelance science journalist based in Brisbane,
Australia. Email: sally@swilkes.co.uk
Andrew Hartley, a ventilatored tetraplegic, seen here competing in the 2004 IFDS Single Person Dinghy World Championships,
sailing full servo assist using a four-way joystick. Taped to Andrew’s chin is a magnet which he can wave past a magnetic reed
switch which activates the jib sheet winch. Andrew passed away last year © Access Dinghy
34 INGENIA ISSUE 27 JUNE 2006 35