Advanced 3D
Modeling Gives America’s Cup Yachts the Edge
John Hardcastle
As history now records, the challenge by
the Italian Team Prada to wrest the America’s Cup from the grasp of the
Kiwis was blunted by the sailing skills of the New Zealand defender.
However, behind the scenes an untold amount of design and development goes
into building any yacht that is good enough to even reach to finals.
When Team Prada finally defeated AmericaOne
(5-4) in Auckland, to take the Louis Vuitton Cup, the syndicate earned the
right to become the challenger in the America’s Cup finals.
The Team Prada victory was the culmination
of three year’s hard work by a vast number of people. Today, just like
in F1 racing, America’s Cup competition is driven by cutting edge design
and development tools. The use of hi-end 3D CAD design and modeling tools, particularly when it comes to designing the hull, keel and bulb of
a boat, is commonplace.
Designing on-screen
Dave Egan, one of three boat
designers for Team Prada, is one person who knew that the Prada boat (Luna
Rossa) had what it took to win the Louis Vuitton Cup.
A New Zealander, Dave is a mechanical
engineer who worked extensively in the aerospace industry. He has spent
many years designing yachts, from Whitbread 60s to hi-tech America’s Cup
challengers. Dave specializes in simulation models using computational
fluid dynamics (CFD) design and modeling software when applied to boat
design.
Dave and the Team Prada designs used the
benchmark Parametric Technology Corporation (PTC) Pro/ENGINEER series of
products to develop the Italian boats that won the Louis Vuitton Cup.
From it headquarters in Waltham,
Massachusetts, PTC develops, markets and supports flexible engineering and
collaborative product commerce solutions for companies. The Pro/Engineer (PTC
i-Series) design system features PTC’s new Behavioral Modeling technology that allows designers to develop products more rapidly and
effectively.
America’s Cup yachts are now designed
under the International America’s Cup Class (IACC) codes that limit a
range of elements including boat length, weight and mast size. With
competitors building boats to the same general specifications, it is
design improvements that separate the teams.
Dave Egan (fourth from the left) and a few
members of the design team behind the winged keel of the Team Prada boat
on the dock in Auckland.
Prior to the America’s Cup finals, I met
with Dave Egan of Team Prada in Auckland to find out what it’s like to
design yachts for the most famous race series in the world.
JH:
When
did you first become involved with Team Prada?
DE: I
was one of the original designers hired by Prada. I was in Japan and I
received a call from Doug Peterson (a fellow designer involved with the
Team Prada operation). Doug and I were involved with Team New Zealand for
the 1995 Cup.
One of the hardest things in America’s
Cup boat design is being able to look at everything that you need to do.
It’s essential to be able to get all of the work done in a short amount
of time.
I realized that it was going to be a huge
task, so as a starting point I became involved with a Whitbread 60 yacht
called America’s Challenge.
JH: Basically, you used
that project as a shakedown for the Prada challenge?
DE: Yes.
We learnt that we could extend the role of our design software,
Pro/ENGINEER. We used the one model, for all parametric modeling and for
the associatively.
For the structural design, we used Pro/MECHANICA
and for the aerodynamic/hydrodynamic design, we used computational fluid
dynamics (CFD). Aside from these tasks, we used Pro/ENGINEER for all the
structural and general design elements of the boat.
JH: This worked well?
DE:
Yes. We’ve huge some huge developments in our 3D design software over
that period. One of the biggest steps forward was with the behavioral modeling
tools.
JH: Did access to better
design software allow you to use a greater range of hi-tech materials in
the Prada boats?
DE: Hi-tech
materials certainly require a lot more design. Obviously carbon fiber composites allow you to orient the
fibers in a certain direction to give
maximum stress. So it’s very important to know exactly what direction
the stress is running and match the material to this.
Like most things, the more hi-tech the
project, the more complicated it is. If you don’t have really advanced
tools, it’s hard to design-in-time.
One of the things about engineering an
America’s Cup boat is you can’t be late! There’s a certain race date
and you can’t say.... "Oh my engineering cycles got pushed back six
months". That’s not an option. That’s one of the biggest
nightmares. You have to make sure that you are on time.
Equally, you don’t want to be ahead by a
month because that’s time you could have spent designing. "
JH: Is it like training
a racehorse, in as much as you strive to peak the boat design at precisely
the right time?
DE: Exactly.
JH: How do you balance
trying to get optimum performance from the materials available but not
suffer structural or design failures?
DE: One
of the big problems with yacht design is that you only have so much power…..the
wind. It’s a critical part of the design process to match your design
with that power curve. We don’t have the option to go out and find a
little more horsepower.
How much power to design for and how strong
to make the boats are the two big questions for all designers. And that’s
the big difference between the 11 boats here in Auckland.
JH: So getting that
balance just right was what you were looking for when you designed and
undertook your CFD modeling?
DE: We
hoped so. The other problem is how narrow do you make the design because
you have to decide on the wind range you’re going to have. For example,
the French boat was optimized for very light winds and Stars and Stripes
for very heavy winds.
So if you’re a general boat and you
happen to go up against Stars and Stripes in 20 knots of breeze, you will
find them very competitive. But if you find the same boat in 10 knots of
wind, it’s not going to be very competitive at all.
That’s where the design optimization comes in, because you have to check your designs throughout the entire
range, which is a huge effort from the computational and the towing tank
side.
JH: You obviously used
the modeling software to make ongoing refinements to the boat?
DE: Yes.
What happens is that you learn more about the boat and how it performs as
the sails are developed, or the seasons change. As we moved forward we
modified, modified, modified.
That’s the idea of having the two boats.
We have a yardstick to measure against. With two boats, we can make a
change to one and see how it compares with the racehorse model.
At Team Prada, we call this the lemon test.
Basically, following a change, you’re out there to see that it’s not a
major mistake.
Often we can’t really see the little
changes out on the water but the on the CFD or Pro/ENGINEER you can see
the changes to any detail.
JH: This process
obviously helped Team Prada during the Louis Vuitton Cup and throughout
general boat development.
DE: Definitely.
What we’ve noticed is that every time we’ve stepped to a new design
generation on the boat, we’ve gone faster. We never stepped backwards.
This is quite unusual in yachting. You
often find that people will try things and like them, but on our boat we
have always taken steps forward."
JH: Are those steps
forward reflecting what the modeling and CFD simulations suggest will
occur?
DE: They
do, and we’ve found that they’re getting more accurate.
One of the difficulties with yacht design
is that the tools you use are not specifically developed for the task.
They are designed for the automotive industry or plastics industry. So
there is a certain amount of tailoring you need to do to make the tools
work well.
In our case, through the design software,
we did a lot of Pro/TOOLKIT work. This allowed us to actually develop
things at program level. In the past, if there was a command you wanted
but it was unavailable, you had to wait for the software developer to put
it in. Now if there is a command I want, I put it in myself.
We did a lot of development on Pro/ENGINEER
itself, to add these little commands and to get the CAD package do exactly
what we wanted.
JH: Being able to set up
your software exactly as you required must have been a big plus?
DE: True.
I first heard about Pro/TOOLKIT in 1996 and that’s when we realized it
could do what we wanted it to do.
One of the things software like Pro/TOOKIT
allowed us to do was to take the Pro/ENGINEER model directly into the CFD
model without human touch. Now, when the CFD modeling computes a new sea
surface on the hull, this is placed back in the Pro/ENGINEER directory.
These are the things we weren’t able to
do even a couple of years ago.
JH: Designing and
refining an America’s Cup boat is such a complex task. How do you use
the information from the skipper or the crew when making small changes?
DE: The
sailors have ultimate say, they’re the people who have the TV cameras on
them and they have to be comfortable with the product.
What the computer modeling does for the
sailors is once they trust it, and I think this happened for Team Prada in
Punta Ala, Italy, in July of this year, the
crew stops worrying about the performance of the boat. Then they focus on
everything else they need to think about.
In America’s Cup racing there’s a high
demand for time spent on the water. The question is, do you spend time
testing designs, sails or race practising? If you can spend less time
testing designs, you have more time for the other things. And that’s
where we are.
Right now, getting one day testing on the
water is a really tricky thing to do. There’s so many things the crew
wants to practice - starts, maneuvering rounds and so on.
JH: The more simulation
you can do, the more this frees up the crew for other things. Is this the
most obvious benefit of using such accurate modeling software?
DE: The
fundamental shift in the technology for us has been twofold. Everything we
currently do is achievable in a certain amount of time.
But the real shift is the time in which we
can now do it. We can look at 40-50 design alterations in one day. When I
first started we would be lucky to get one out in a month!
Once we had a good design, we actually
manufactured off our design models. We didn’t have to do the usual,
which is going back and design it again, then rebuild. We just sent the
whole thing off to manufacturing.
If you assume that everyone here down the
street (all 11 America’s Cup challengers are based along a single
section of waterfront in Auckland harbor) are smart designers, then the
more that you can squeeze into the time you’ve got to design, the more
likely you are to come out in front.
JH: Basically, you finalized
the boat design using the modeling software?
DE: We
didn’t do any wind tunnel testing at all, which is very unusual. We
relied on numerical simulations for the keel work. Everything you see out
there (Team Prada unveiled one of their boats to the media and the public
after winning the Louis Vuitton Cup) hasn’t seen a wind tunnel.
For the hull work, the computer and the
towing tank work hand-in-hand. What happens is the tank is like the broad
stroke. It gets you a base, a playing field whereas the CFD lets you go in
and look at things in great detail. But the two exercises give you
different information.
The towing tank gives you the drag, you get
one number whereas the CFD gives you all the pressure fields and
everything around the boat. When you put the two together, this becomes
very powerful.
In fact, the more CFD work you do, the more
experimental work you want to do to back it. Another way of looking at
this is that in the past, CFD was mainly done as an afterthought to the
towing tank testing. Now towing tank testing is becoming a validation for
the work done in CFD.
The actual design work is done in CFD and
from time-to-time you go off and test in the tank to make sure you know
what you’re doing. That’s the way things are heading. Having said
that, the two things are still equally important because once you have
done the CFD work, you have all these added questions needing answers.
JH: How important was
the CFD modeling when it came to designing the keel and the bulb?
DE: The
real game under the water is to reduce drag. The way we approached this
task was to make lots of incremental changes.
Before that, it’s important to decide
what concept to run with. You look at a wide range of possibilities, make
a decision and then spend time optimizing the design.
The difficulty of yacht design in CFD is
that you have an extra problem created by the water. If you are building
an aircraft or a car, the flow is always around it. With a boat, as it
changes speed, the amount of wave or surface that it encounters changes.
So if you want to accurately use CFD on the
area under the water, it's essential to be able to deal with the new
computer wave surface. At Team Prada, we joined Pro/ENGINEER and ICEM
together and had the two systems update each other.
The other part of the puzzle is that every
time the pressures change on the boat, it floats differently. That is, is
bobs up and down. This happens at the same time as everything else is
happening.
Although it sounds complicated, and it is,
the nice thing is that when you put all the programs together, they take
care of everything. Once we did that, we had very accurate measurements.
We actually calculated the sea surface waterline on our boats to within
two tenths of a millimeter.
JH: With such powerful
design tools now available, are teams reaching the limits of design in the
current IACC class of racing?
DE: No.
We’re as close as we can get to how good a boat can "easily"
be designed through traditional methods. The gains are getting harder and
harder because we’re at the end of the curve. But the gains are
defiantly there, we just have to work harder to get them!
For example, the bulb on the boat unveiled
today. It took five months of intense engineering to get there. We found
the design to be significantly better than what we had, but two of us
still had to put in five months of engineering to get it.
The way to beat the time cycle is to make
the tools more powerful. That’s why I’m convinced that we’re on the
right path. The only way to move forward is to compute everything more
accurately and quickly.
The two things have to go together. There
are some very good tools out in the marketplace that will do nice things,
but they might only give one or two answers every six months. That doesn’t
help you if you need a thousand answers.
JH: So the ideal is
super practical and powerful modeling tools.
DE: The
design tools have to deliver the right balance.
JH: What’s next for
you after the America’s Cup?
DE: I’m
not sure if anything will consume my life like the this has for the past
three years. I’ll probably undertake some consulting with PTC with their
aerospace and automotive clients.
Traditionally, the CFD process has involved
designing a CAD model and looking at IGES
data. You then construct a mesh model by hand and run the CFD program,
from which you get a result a month later. My passion is to bring all
these things together as part of a streamlined process.
But once the finals are over, I’ll
probably take a vacation for a month or two."
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