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‘It’s no longer just a sailing competition ‘ says Jerome Milgram,professor
of ocean engineering at the Massachusetts Instuitute of Technology and designer
of four out of the five US yachts which originally entered.’ It’s a technology
competition.’ Indeed it is.

Faster and lighter boats than ever before will be sailing close to the
edge of what physics permits,equipped with on-board computers and sophisticated
software to gain the edge over their opponents. Each is the product of computer-aided
design and has been engineered to the specific conditions prevailing off
San Diego. ‘The boat that wins’ suggests one naval architect ‘could fall
right apart after crossing the finishing line.’

The finalists are also the costliest boats ever to race for the cup,
a ritual which started in 1851 when American yachtsmen threw down the gauntlet
to their British counterparts. They are a testament to teams of engineers
who have made function the equal of sailing’s traditional affair with form.

Both finalists conform to the specifications of a new class of boat
introduced in 1988 after heated controversy – the International America’s
Cup Class. This set limits on draught (the maximum depth of any part of
the boat) length, weight (displacement),sail area and beam (width at the
widest part of the boat). But it gave designers more leeway to build bigger
and faster boats than the so-called ’12-metre class’ which had competed
in previous races.

The latest contenders average 42 metres long, weigh 21500 kilogramss,
have masts which reach over 30 metres above deck and carry 50 per cent more
sail than the 12-metre boats. Their hulls are made of a thin skin of carbon
fibre laid over a honeycomb core (usually a nylon-coated paper called aramid.)
The composite has a better stiffness-to-weight ratio than the aluminium
used previously.

The new designs owe their form largely to a new computer model, known
as the Velocity Prediction Program or VPP. It takes into account basics
like length, draught, sail area and weight but can add in factors such as
drag and lift created by keels and rudders, coefficients of wave resistance,
friction and similar obstacles to a boat’s speed.

Yacht designers have to satisfy conflicting demands, especially in the
area where water and air meet. ‘A full-blown analysis of a boat in water
is about as complicated as any there is’ is how naval architect Robert Ranzenbach,
a consultant to the Partnership for America’s Cup technology (PACT) sums
it up.

Wind whips around a boat, its sails and rigging in an ever-shifting
pirouette. The wind speed and direction can vary at different points,at
the water’s surface, deck level, the middle of the sails and at the masthead.
This uneven distribution or ‘rotational flow’ makes modelling sail geometry
the least exact of the design procedures: but trials off San Diego have
shown that simply lightening the sails pays off.

DRAG IN THE WATER

Hydrodynamic drag is another difficult force to calculate. VPP models
use formulae which account for both drag due to water viscosity and induced
drag (created when vortices stream back from the trailing edge of a keel
in the same way that air streams back from a plane’s wings).

Nothing is more likely to keep an America’s Cup designer awake at night
than the shape of the hull – the real key to speed – especially its performance
in waves created by the boat itself. A yacht’s bow sets up waves, small
ones at slow speed but becoming longer and higher as the speed increases.
Ultimately these can reach a point where there is a crest at the bow, a
trough underneath the entire boat and another crest at the stern. The waves
carry away energy and, as the boat goes faster, its wave resistance increases
geometrically until it exceeds drag due to friction. Then more sail power
has to be called up.

Also crucial is the design of the keel, which accounts for 30 per cent
of a boat’s overall drag. The keel is essentially a wing extending straight
down amidships from the hull. It keeps the boat from sliding sideways by
‘lifting’the boat forward and suspending ballast in a bulb, called a ‘pig’,
from its nether end. Anything which will reduce keel drag can win races
and the designers have been tinkering with them up to the last moment, concealing
their boats behind shrouds when hauled onto dry land.’ Those keels are our
most tightly kept secret,’ says Donald Peters, a designer with the America
3’s syndicate.

Nobody yet knows how fast the boats can go but the winds off San Diego
have so far pushed them to 15 knots.

On-board computers can provide data on how fast a boat has sailed previously
in a certain windspeed and direction, compare that with its current performance
and tell the crew when to switch to another sail to maximise speed.

‘Computers give you a video performance rather than a snapshot’ explains
Jim Marshall of Ockam Instruments in Milford, Connecticut (which has provided
much of the intrumentation in use in the cup.) ‘For example, while sailing
upwind on a particular course,your speed may average 7.8 knots but vary
from 7.5 to 8.1. Precisely when did you hit 8.l knots? Can it be sustained?
The computer can tell you and that 0.3 knot difference could mean a 14 second
advantage per mile’.

Skippers also use their on-board computers to work out where they are
along the course, where the opposition is, how fast their boat is travelling,
which side of the course is being favoured by the wind at any one moment
and what wind shifts may be expected from past patterns.

The precise position of a boat is calculated using the Global Positioning
System satellite(GPS). Ockam Instruments have developed a program which
computes position, windspeed and direction and distance-to-go as a boat
approches the starting line. It gives the skipper data on how long it will
take him to reach it.’ When we first tried it out ‘ said Jim Marshall, ‘skippers
complained that they were crossing the line two or three seconds before
the gun. We discovered that GPS had a time delay. We had also goofed by
fitting the antenna to the stern of the boat. Things have to be very precise
in this business.’

Between 1851 and 1983, the US won every race except the first. Then
Australia, using a technological breakthrough – the famed winged keel –
spirited the cup away. The winged keel reduced drag and put more weight
deeper into the water, in effect lowering the boat’s centre of gravity and
improving its righting moment so that it would sail more smoothly and efficiently
in strong winds.

Chastened, the US developed its own wings and in 1987 Dennis Conner
won the Cup back in windy Freemantle, Australia. One year later, New Zealand’s
Michael Fay, a wealthy businessman, built a juggernaut of a boat, 37 metres
long,but it lost to Conner’s lightweight catamaran. Conner also won the
legal battles over allowable designs which followed.

The 1983 American reverse undoubtedly rekindled interest in the cup.
Millionaires with sailing envy bought their way into the competition with
hired skippers and the best technology that money could buy.

Two US syndicates have raised the money for this latest defence of the
Cup. Initially eight yachts fought to challenge them – from Sweden, Spain,
New Zealand, France, Japan, Italy and two from Australia. Three months of
races have winnowed the field to one defender and one challenger.

The eliminating races prompted cloak-and-dagger antics worthy of the
Cold War. A member of the America’s Cup organizing committee accused Paul
Cayard, American skipper of the Italian contender, of betraying his country.
A French sailor was dismissed from his team in March after he was caught
diving near the New Zealand boat, presumably trying to take a peek at its
keel. Armed guards were used to protect syndicates’ compounds. According
to a source associated with William Koch’s America 3 syndicate, security
at their compound in San Diego is in the hands of a former member of Israel’s
Mossad secret service.

No one has applied more science – and money – to this race than Koch,
a businessman who has spent about $40 million and raised another $20 million
to sail four boats in the trials. He believes that the emphasis on high
technology has paid off. His America 3 syndicate tested its hull shapes
in towing tanks and its keels in a wind tunnel, then evaluated the data
on their VPP. But Koch and his designers at MIT wanted something closer
to real life. So in a dry dock near Boston they built their secret weapon
– the dynamometer.

The dynamometer is an 11-metre boat similar in design to the IACC boats
but built of wood and epoxy. Its rig, however (mast, sails and the shrouds
that hold them up) is fixed to a rigid frame set within the hull and connected
to it through six load cells. Each one measures the tension and compression
created by sail forces. Gauges set amidships measure the largest force,
the ‘overturning moment’ which is the side force created by the wind against
the sails. Another gauge at the stern measures ‘pitch moment’, created by
wind and the pitching of the boat. Roll and yaw are similarly measured.

SCALED UP TO FULL-SIZE

The dynamometer was sailed like a normal boat and the effects of changes
in direction, sail trim, and equipment recorded every 10 seconds and stored
on computer files. The mathematical models were then entered into the VPP
and finally into the computer programs of the full-size boats.

All the boats which have been racing off San Diego have design advantages
and disadvantages. For example, one with a narrow canoe body and less wetted
surface area than most drove well through waves but tipped more easily and
needed a heavier keel. A beamier boat, broader amidships with a shallower
body, proved less likely to tip and could be built lighter. But it was retarded
more easily by waves – even the chop from spectator boats.

Trading one advantage for another ‘is like trying to nail jello to a
wall,’ says designer Karl Kirkman of Science Applications International
Corporation (SAIC), which has been designing Cup boats since the 1980s.

Another headache has been the exceptional flexibility of carbon fibre
spars. Devices that measure wind direction are mounted to the rig and must
compensate when spars twist in the wind. A one degree error in measuring
apparent wind (the sum of wind over the water and wind created by the movement
of the boat) could cause a skipper to steer four degrees off course.

To help keep a constant eye on the sails, video cameras have been installed.’
The sails are so big’ says Marshall ‘ that otherwise you would lose perspective
and depth of field.

Most competitors built at least two boats – Koch had four and the Italians
five – to find the ideal compromise for the different variables. New Zealand
probably went the furthest with their beamy boat believed to be about 2000
kilograms lighter than its rivals. To add to its waterbug performance, designers
fitted a tandem keel with two small fins instead of one, so reducing the
wetted surface area. They eliminated the rudder, steering instead with trim
tabs, or louvres, on the keel fins. ‘It’s very hard to steer,’ comments
Jerome Milroy ‘but the Kiwis made it work.’ They paid a price, however –
the yacht’s rough water performance. San Diego has unusually rough water
in relation to the wind conditions, which are usually less than 10 knots.

‘There is absolutely nothing half so much worth doing as simply messing
about in boats’ wrote Kenneth Grahame in The Wind in the Willows. The statement
is no less true for the America’s Cup scientists and engineers, who have
replaced intuition with algorithms. Whoever wins, we are likely to see the
best marriage yet between technology and the elements.

Chris Joyce is a yachtsman and freelance writer.