America’s Cup - Report

Prada Cup: Weekend Two

February 12, 2021
Yanmar Holdings Co., Ltd.

YANMAR, the Official Marine Partner of the 36th America’s Cup brings you pro-sailor Sam Gilmour from Yanmar Racing who will present a series of articles breaking down the details of the America’s Cup racing and giving us his unique perspective.

By Sam Gilmour from Yanmar Racing

America's Cup Final Report
Prada Cup Final, Weekend Two
Prada Cup Final Races 1-4
Prada Cup Semi Finals
Prada Cup: Weekend One

Welcome back to my analysis of the 2021 America’s Cup, on behalf of YANMAR who are the Official Marine Partner of the 36th America’s Cup.
I’m Sam Gilmour - part of Yanmar Racing and am looking to delve into the racing and the competitors behind it. Last week, our first taste of racing, saw incredible racing and absolute carnage - culminating in the American Magic team coming moments away from sinking following a major high speed capsize.

I’m going to run through the major points of difference on the AC75 class yacht and explain where the team designers are looking in finding an edge over their opposition.

Weekend Two of the Prada Cup saw the completion of the round robin stages - albeit with just two teams hitting the water, and just one race - Luna Rossa Prada Pirelli and INEOS Team UK.

Based on the Previous weekends points situation, and due to the American team being off the water, Luna Rossa needed to win two from two in the races scheduled to qualify for the Prada Cup final, with INEOS just needing a single victory in their hunt.

The loser of these teams was bound for the semi-finals, where they would match up with American Magic, who are looking to bring their boat out of the shed following extensive repair work.

Ultimately, it was INEOS who came through, booking their ticket to the finals. But it was not before an enthralling wire-to-wire race that saw 9 lead changes, and a final cross that left many wondering.

The AC75

The radical design of the AC75 sees a number of features never before seen in yacht racing and includes design elements that will bring changes in the wider sailing world for generations to come.

Certain components of the boat have been provided to teams, with the idea they are identical and changes in design are not allowed. These components include the foil-cant system, foil arms, masts and rigging. Below is an explanation of some of the more unique features in the class.

Foil-Cant System
Firstly, the foil-cant system (FCS). A revolutionary system developed for the America’s Cup that help to allow the boats to reach speeds similar to that of their catamaran predecessors, giving the monohulls enough of righting moment to stop them from capsizing when stationary (like a keel), acting as the foil when sailing at speed, as well as additional ballast on the windward foil.

The FCS is one-design, meaning all teams have identical systems. It is powered by onboard batteries, that allow the hydraulic rams to raise and drop the foil depending on the needs of the team. The FCS has not been without its critics, and teams have had significant difficulties at different points with their systems - mostly in relation to the software bugs, when it comes to controlling the foil positions. When the boats are being sail, much of the onboard noise comes from the foil hydraulics in the background as they are continuously trimmed and adjusted.

The Foils
Owing to one design nature of the FCS, the major development focus in this class is on the shaping and designing of the foil, and from a distance, it appears this will be the deciding point of who wins this America’s Cup. What we have seen so far is four significantly different foils shapes from each of the teams, proving to have different strengths and weaknesses depending on their foil shapes. American Magic, who have the smallest ‘area’ foils, look strong when the wind is up, however have been struggling as the breeze gets lighter.

The differences in foil shapes between teams

Teams are limited to building 6 ‘main’ foils for the entirety of their America’s Cup campaigns, meaning 3 sets of two foils, as well as four rudders. Because these are particularly complex components, the building of these take many months. As such, design decisions have been made well in advance of what we are seeing now.

Teams can modify existing components, however they are limited by a ’20%’ rule, such that no more than 20% of the mass of the foil can be changed. This obviously limits the scope of changes they can make, and may mean a teams’ maximum boat performance has been already decided long ago.

The other unique component on the AC75 is in the sail plan, particularly, the twin-skin mainsail, that was developed with the intention of being able to be raised and lowered as a traditional sail, with the added performance of what is seen on the rigid wings on the previous generation America’s Cup class. The twin skin, effectively means two sails are raised side by side, allowing the skins to be trimmed independently, and allowing more control over the sail shape. Sail efficiency is something that is critical in boats doing upwards of 50 knots, and it is important to be able to put more shape in the sails when the boats are at low speed. This has proved difficult thus far, and will be interesting going forward on light air days.

Interestingly, teams are using vastly different approaches in how they are trimming their mainsails. INEOS and American Magic have both elected to go the ‘traditional’ approach, utilising a boom at the bottom of the sail, whereas Luna Rossa and Emirates Team New Zealand using a series of hydraulic rams to control the sails, with no boom onboard.
These approaches have different strengths - a boom allows for more precise trimming position, as well as a tried and tested approach to controlling the mainsail shape, whereas the boom-less approach allows the sail aerodynamics, and the ‘end-plate effect’ against the hull to be maximised (with no boom to act as an impediment to air flow). As this America’s Cup goes on, this ‘end plate effect’ appears to be a critical feature of the hull shapes themselves.

The jibs are also interesting, as the teams can switch sails depending on wind strength. We have already seen teams struggling with a late sail switch, and this could be something to watch closely going forward. American Magic missed the beginning of a start due to a late sail switch already - so will need to be careful as to not make this mistake again going forward.

Code-zeros, larger jibs built for downwind and lighter winds, were also a feature integrated into the class - with all teams required to add a bowsprit to the boats. Thus far, we haven’t seen any teams race with a code-zero, and I believe we will not at all. Manoeuvres are critical in the AC75, and it seems that the code-zero is a significant impediment to tacking the boats, such that the boats tend to fall off the foil in a tack - something in itself that would be a race losing error.

The development in hull shapes is changing rapidly, as teams are learning and developing more and more. Teams were allowed to build two hulls, using the first as a development boat, with the second being primarily as the race yacht. We have seen big changes between designs, in particular relating to crew aerodynamics and hull shapes under the water.
In ‘second version’ boats, we are seeing all crew hidden below the deck of the boat, with just the helmsman or tacticians heads poking out, obviously, so they can look around to make strategic decisions! Team New Zealand have even elected to have all crew fully hidden from sight - one can only question how they will make decisions in close situations without being able to see around.

Secondly, the hull shapes on the bottom are changing significantly, with the lowest point on the hull being the most interesting. All teams have added a radical ‘bustle’ shape, a straight, keel-like component to the bottom of the hulls.
The idea behind this is to help partition airflow around the hull, which actually improves the performance of the sail plan. Ideally, hulls need to be as close to the water as possible, which stops air from escaping from one side to the other - this creates an extension of the pressure differential (similar to the sails), eliminating a ‘stall’ in the air flow and improving the aerodynamics of the boat.

As we go on, we will likely see more radical changes to the boat, and this will only add to the intrigue of what is the oldest trophy in world sport.

Round Robin Race Eight

It was INEOS and Luna Rossa who hit the water on Saturday, with 15 knots and gusty, shifty conditions. The race started amazingly close, and it was Luna Rossa, who had an early lead, with skipper Jimmy Spithill able to luff INEOS slightly on the upwind - forcing them into a tack, and falling off the foil in the process. This was a well-executed manoeuvre, as they looked to be in a difficult position - I hope that the racing becomes closer as we go on, with these situations becoming more commonplace.

Following this, it was a bad tack by Luna Rossa at the top mark allowing INEOS to slip into the lead at the rounding onto the next leg. With Luna Rossa just 50m behind at the bottom mark, they elected to split at the bottom gate - a nice move getting them in phase with the wind, and into a 200m lead.

Tactically, the course was difficult for tacticians, and I believe keeping the opponent close needed to be a primary focus, due to the unpredictability on the conditions.

They hung onto this lead for the next lap, however a clever manoeuvre by INEOS rounding the bottom mark - with an early windward foil drop, that enabled them to tack around the mark. Luna Rossa were slow to follow, and ultimately the lead changed once again.
For me, this was the biggest tactical mistake in the race - Luna Rossa needed to be able to stay with their opposition and manage their lead.

On the final cross coming into the finish, there were more fireworks - Luna Rossa protesting INEOS in a tight port-starboard situation, where the umpires saw no infringement. It was a close situation, and the umpire call ultimately decided the race result.
If you haven’t watched the race, I recommend looking back on the racing - having the boats so close together was simply incredible, and perhaps just 1 or 2 metres made up the difference.

Essentially in this race, Luna Rossa made too many mistakes, with a couple of poorly executed tacks as well as some basic tactical errors, it was the British team who were able to capitalise. Sir Ben Ainslie, skipper of INEOS, mentioned following the race that they had some issues adjusting their Cunningham - one of the main controls on board. It will be interesting seeing them race next, as perhaps they have more boat speed potential.

This race gave INEOS an unassailable lead in the round robin stage - putting them straight through to the Prada Cup finals. For Luna Rossa, it would be a hard pill to swallow, now needing to race American Magic in the semi-finals for a finals spot.

The big advantage of the direct finals berth is the additional development time INEOS now have. They have time to implement a number of improvements on the boat, which otherwise may not have been possible. On the bright-side for Luna Rossa, I believe the race practice will be to their advantage, as they will be able to flesh out any tactical mistakes in the upcoming races. Whether they can get past American Magic coming out of the shed, will be another question all together.

From on, every race matters. Things will begin to get even more interesting going forward!

Next report