How to Win the America's Cup with CFD

People have been designing boats for literally thousands of years. Triremes, fishing boats, tea clippers, galleons, battleships, aircraft carriers, cruise ships, oil tankers, dinghies, and many more.  Historically, a lot of this design was done using models. You would build a model of the hull and put it in a tank of water, and tow it. People have also been racing boats for a long time too. This post is mostly about the America's Cup. This started in 1851 with a race around the Isle of Wight (that island in about the middle of the south coast of England). It was won by a schooner called America. The name America's Cup comes from that first winner, not because the trophy, the Auld Mug, was held at Newport, Rhode Island, and the races took place there for many years. It is the oldest international sporting trophy in the world.

The rules have changed a lot over the years. One rule is that you have to be attached to a national yacht club to participate. This means that the number of possible participants is limited, and each is a sort of unofficial national team. There are also rules about the number of resident versus non-resident crew on the boat too.

Whoever wins the cup is the defender in the next series. Someone else is the challenger. Until 1970, there was only one challenger, but that year there were several, so a selection series was held to decide who was the official challenger, and that has happened every series since. There are a new set of rules for each series, established by the defender together with the challenger (and their lawyers!). Like in Formula 1, the rules are tight enough to have similar boats but loose enough that there are a lot of opportunities for design improvements. Although obviously, the race happens on the water, there are about 3-4 years of development before the boats are built.

Design

So how to design the boats? People did model testing, design a small version of the boat with specific features, and then extrapolated from the model scale to full scale. The model was tested in a towing tank or, more recently, in wind tunnels. Even more recently, using computational fluid dynamics or CFD. Then, if you were rich enough, build a full-scale boat and see how it sails in real water (of course, the models were towed in real water, but the ratios of things like viscosity and dimensions vary, so it is not a perfect model of reality).

Again, as in Formula 1, there was a problem that the team with the most money would tend to win. So to get the competition closer, there have been increasing limits on the duration of the test period and what can be tested. The number of test boats is limited. Teams cannot use continuous modeling. Right now, the teams are limited in model testing, and so the  America's Cup is CFD-only.

The boats used to be quite slow, floating in an Archimedean way. The event was not that interesting to follow and not much televised. Since the San Francisco America's Cup was held in 2013, we have been in the "foiling" era of the cup. Now the boats are flying with an aerodynamic lift from a hydrofoil. These boats have evolved from catamaran (two hulls) to very unstable single hull designs. They now fly much more than before, 100% of the time during a race. The design of the hydrofoils is dominant. In fact, the speeds are now so fast that air becomes a big part of the design. There is so little of the hull in the water that drag is about 50:50 between water and air. Both air and water are fluids, of course, so CFD is used to model both at the same time.

The design of the hydrofoil is a compromise between lift and drag. If it is optimized to fly in low wind, then there will be too much drag in high wind. If it is optimized for high wind, then it won't fly properly in low wind. Goldilocks' porridge.

The next America's Cup is the 37th. It will be held in September and October 2024. The last winners, Emirates Team New Zealand, picked Barcelona for the event rather than its home base in New Zealand like last time. If you want to go, book now. Here's an amazing animation of how Airbnb has moved into Barcelona. You don't need me to point out how this is making it tough for locals. But if you want to go and see the America's cup in 2024, then you have to be a dot (or stay in an even more expensive hotel).

The first phase is purely design. The defender and the challenger of record meet to create new rules for the boats. Then a book of rules is shared with anyone who wants to challenge. Then the design phase starts, with the need to design a boat that will be competitive. At this point, there is one defender, one challenger of record, and some other challengers. There will be a race, known as the challenger series, before the proper America's Cup to decide which team is the true challenger. The final winner of that series goes on to compete one-on-one with the defender.

The next America's Cup will be defended by the last winners, "the Kiwis," or more officially "Emirates Team New Zealand". The challenger of record is INEOS Brittania (UK). The other teams are Alinghi Red Bull Racing (Switzerland), Luna Rossa Prada Pirelli Team (Italy), and NYYC American Magic (US). NYYC stands for New York Yacht Club.

Three of those five teams have picked Cadence's FIdelity Marine software for their CFD simulations. Emirates, INEOS, and NYYC. The Kiwis have been working with NUMECA, now Cadence, for four or five America's Cups and have won the last two.

Cadence Fidelity Marine

Len Imas of the American Magic team explained why it picked Fidelity Marine:

American Magic has selected the Cadence Fidelity Marine software as its primary CFD tool for hydrodynamic analysis and design as it continues to provide state-of-the-art numerical simulation capabilities for marine applications. Among commercial and research codes in use today, it remains the industry leader over the course of multiple America’s Cup campaigns by providing robust and accurate results and expanding functionality in areas involving high-performance hull and appendage design analysis, marine vehicle dynamics, and fluid-structure interaction.

Amazingly, the rules are now so strict that you can't use models anymore. When these boats hit the water for the first time just a couple of days before the challenger series, it is the first time they will sail. The rules for the race are very clear, and you can't just do a lot of sailing beforehand, just like you can't build your own Formula 1 racetrack and use it continuously. There are very specific rules about exactly when you can fly the boats (nobody says "sail the boats" anymore). 

The next America's Cup will also have a race for women, for the first time, and a return of the one for young people. They will use smaller versions of the next boat. These will be held in Barcelona too.

There are obviously a lot of very detailed rules, but the high-level changes, mostly focused on getting the cost down without hindering innovation, are:

• Teams are only permitted to build one new AC75
• Limitations on the quantity of foils and componentry that can be built for the AC75’s
  
• Introduction of the multipurpose One Design AC40 class, which teams will be able to convert and use for testing, component development, and Match Race training
• AC40 class will then be converted back to the measured One Design AC40 class for use in the exciting new America’s Cup Women’s Regatta and America’s Cup Youth events. These events have been developed to create new accelerated inclusive pathways into the America’s Cup for the growing global talent pool of female and youth sailors
• Race crew onboard the AC75 reduced from 11 to 8 sailors
• Further One design elements
• Shared team recon
• Supplied starting software
• The AC75 class of boats will be maintained for the next two events

Video

Another thing that is new is that a condition of entry is to participate in a behind-the-scenes documentary. I assume everyone has seen the success of Netflix's Formula-1 Drive to Survive and wants to create the equivalent for yacht racing and the America's Cup.

In the meantime, while we wait for Netflix to do their version, here's the Designed with Cadence version (2 minutes):

And a sneak preview of the first AC40 of the 37th America's Cup, almost ready to be delivered to Emirates Team New Zealand, the defending team:

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