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Stoneways Marine 2021 - LEADERBOARD

America's Cup Rialto: Feb 19 - Some key differences between the Finalists

by Richard Gladwell, 18 Feb 13:54 GMT 19 February 2021
Francesco Bruni makes a point to Jimmy Spithill over afternoon tea - Luna Rossa - Prada Cup Finals - Day 2 - February 14, 2021 - America's Cup 36 - Course E © Richard Gladwell /

On Sunday, we were onboard the TV photo catamaran, which was a novel experience - and allowed a different shooting angle - albeit it against some challenging G-forces, as the boat abruptly changed course.

The racing was held on Course E for the first time - although we have been there for seven days of Practice race sessions - and it is used by the teams for most of their speed testing.

Forecasts of strong winds and big seas triggered the change from the Stadium Course C and Course A.

Having lost two races on the first day of racing on Course A in ideal if changeable sailing conditions.

INEOS Team UK failed to win two races, the same as Day 1 of the Prada Cup Final and is now at 4-0 on the leaderboard.

Out of four races sailed to date in the Final, INEOS Team UK has made starting errors of varying degrees in three of them.

Maybe it is a bit harsh to label their falling off the foils in Race 1, as a starting error. There was a soft spot in the breeze, dropping down to 4.4kts, which Luna Rossa saw - telling the starboard, and starting helmsman Jimmy Spithill not to go up and to make sure he stayed foil-borne. He did this and Luna Rossa got through the hole in the breeze, and was away.

From what we've seen on the water, the ability to spot changes in breeze strength and direction is the key difference between the two boats, who are getting around the course at remarkably similar average speeds - according to the on the boat information available through the online version of Virtual Eye. (In this version the viewer can break the race down and watch the key points in the race, from various perspectives, and in conjunction with some other tools that are available such the onboard video and audio, as well as the two produced and commentated video feeds.).

The second race of the Finals was much closer at the start with INEOS technically winning the start, by less than a second and in a controlling position. However as is often forgotten by commentators, it is not who wins the start that matters, but as in your father's America's Cup, who wins the first cross - which can take place several hundred metres up the course.

Most fans are still thinking of the start in the same way as the 2013 and 2017 Cups, where the first leg was a fast reach followed by a downwind leg, and the first upwind cross did not take place until the third leg. In that context who got the jump at the start, by definition usually got clean wind and a significant advantage.

In Race 2 on Saturday, Luna Rossa tacked away from INEOS Team UK soon after the start, got a better breeze out to the right and were ahead at the first cross, occasionally sailing faster, but usually with a better VMG (Velocity Made Good, or speed toward the next mark rather than speed over the ground). Although the margin was only 11 secs at the first mark in the sea breeze, on that course there are no passing lanes - and Course A in a seabreeze is something of a Soldiers Course.

Back to Sunday.

The strong breeze and sea state forced the Race Committee to race on Course E in the Tamaki Strait between the mansions and vineyards on Waiheke Island and the mansions on Eastern Beach.

At the start of Race 3, INEOS tried to "hook" Luna Rossa at the start but was not close enough and missed getting control. The Brits were forced to bail and take the other end of the line, going for the right hand side of the course. Pulling off a move like that and missing is unfortunate but not necessarily race determining. Officially the Brits were 9sec behind at the start, but had clear air and were in contact.

This turned out to be their closest Finals race to date against Luna Rossa. They closed the margin out to just 6 secs at the bottom (Mark 2), but dropped 13 seconds on the next beat.

However that was not the point of difference in this race. Virtual Eye shows that the gains made by Luna Rossa were the result of spotting better wind pressure and taking advantage of it. Getting into more wind pressure pays a big dividend in the AC75, due to the fact that the wingsailed monohulls sail in multiple of two or three times the speed of wind. The advantage is that upwind the leader extends as they get into the stronger breeze, but downwind the chaser should be able to reduce the margin.

However the wind spotting ability of Luna Rossa was so good that the Brits couldn't make an impression. And of course rounding to top mark for the final time the lead in metres gets stretched due to the leader being the first onto a faster point of sailing - often 10kts faster. The Italians only picked up an extra 30 metres to take their lead from 120 metres to 150 metres after the Brits had rounded. Luna Rossa overstood Mark 5, preferring to spend some of their lead to keep a tight cover on the Brits, who tacked short of the lay line for the Mark 5 gate.

The stats for the race had it that Luna Rossa did 26 tacks/gybes to the Brits 25. Average boat speed was very close at 37.31kt for Luna Rossa and 37.02kts for INEOS Team UK. The Italians sail the greater distance 29,494 metres compared to the Brits 29,334 metres. The stats would tend to belie claims that the British are slower than the Italians tacking and gybing. They do support the view that the boats are very close in speed. The longer distance sailed by the Italians is probably attributable to the Italians having to spend some of their lead to maintain a tactical advantage over the British.

This race was the closest the two teams have had in the Finals.

Between races the fresh breeze dropped and then started to recover, except instead of the rounded puffs of increased breeze moving across the surface on Race 3, the breeze came back in long streaks.

While the Brits had a mare of a start, after they somehow lost control of their foils in a critical part of what looked to be a good approach, and fell off their foils in spectacular fashion, but managed to control the damage.

The difference between the boats was again the way they were able to read the wind, but instead of the increased pressure giving a better speed, the difference on Virtual Eye appeared to come from a better VMG sailed on occasions giving the Italians a very nice jump - usually in the space of just a minute. But add a few of those up over the course of a race, and the result is a very handy margin - again magnified by the AC75's ability to sail at multiples of the windspeed.

The VMG theory is supported by the race stats where Luna Rossa sailed 27,467 metres compared to 27,631 metres for the Brits. Despite the race being hailed as a tack-fest Luna Rossa did 22 tack/gybes compared to 18 tacks/gybes for the Brits - again indicating the Italians were playing the shifts and VMG game, without the need to cover quite as tightly after a very marginal boundary penalty on Leg 3 against the Brits, which doubled the Italian lead from 10secs to 20 secs. The tack-fest claim is hard to sustain when for the race leader there were actually four less tacks by the Italians in the second race of the day, than the first.

To our eyes the Italians have a big advantage in the wind spotting department with their twin helmsmen approach - and with Spithill driving from the Starboard side (and being the primary starting helmsman). On the water, and not seen on TV, it is an easier task to keep track of the breeze if your perspective doesn't change. This is particularly so on the AC75's which are sailing at 35-36kts upwind, and another 10kts or more downwind. The Italian system allows one of the helmsmen to have a look around when the other is driving. There is an almost relaxed discussion between Spithill and co-helm Francesco Bruni about the breeze all around the course. The mainsail trimmer does swap sides between tacks and gybes - but he is the only one to move.

On the British boat the style of conversation is a lot more along the standard communication style from wind spotter/tactician to the skipper, the tenor seems to be more urgent and not as casual as the Italians, who seem to have each other tuned in and are really just updating each other.

Both helmsman Ben Ainslie and tactician Giles Scott swap sides each tack and gybe along with the mainsail trimmer. To add to the traffic, downwind, Scott often comes out of the leeward crew trench to go back to the end of the boom/aft deck to have a quick look to windward and behind before running back to his leeward spot. It's all very animated aboard Britannia, while there is minimal movement aboard Luna Rossa.

Certainly the British approach is conventional, where the helm swaps sides each tack/gybe and the other two crew would do the same. But it doesn't seem that the standard approach works that well aboard the AC75. Things certainly happen very quickly sailing at 35-50kts - and it may well be that the Italians have found a better approach for reading the vital wind signs and converting those into an effective tactical strategy.

The other striking difference between the two finalists is the skirt at the bottom of the mainsail.

Luna Rossa, like ETNZ seem to be using a floating clew, which doesn't use a mainboom. The British have the standard mainboom setup. The effect of the spar is for the bottom metre of the double skinned mainsail to be quite distorted as it passes over/around the boom. It doesn't form a good seal with the deck to create an endplate on the rig.

Luna Rossa's mainsail on the other hand has a nice clean consistent shape all the way down to the deck, where it forms a nice tight seal, and sets up the endplate effect.

It is surprising given the emphasis on drag reduction, development of maximum power from the mainsail and obsession with developing endplates to reduce cross flow and turbulence that the Brits have not come up with a cleaner solution in this area.

Max Sirena made reference to the changes made to Luna Rossa in the Pre-Finals Media Conference.

He listed sails and foil wings - which would be of no surprise. They also say they have a new mast. Given that the external dimensions are fixed and there is a minimum laminate specified, the implication is that they have beefed up the laminate in the spar - and differently from their previous model.

The indication is that they have taken on the feedback from their Recon team, used the Kiwi setup as a starting point, and then made their design moves from there. Of course integrated these with the new mainsail. That points to a more powerful setup - and trying to leapfrog the ETNZ version, rather than a straight copy of something they know works and is faster than their previous setup.

As with all AC75's the various differences must be integrated and that synergy used to maybe achieve a better result than the sum of the parts. The speed between the two boats is probably quite minor. It is surprising to see the average speed around the course quoted by Virtual Eye as having a delta measured in a few tenths of a knot.

However on the water, the Italian boat does look to be the easier to sail, and the more forgiving of the two, and seem to have less handling errors - although the Brits are fast when set up properly.

In short the Italians seem to have a wider sailing groove than the Brits.

In the end it comes down to applying the old formula of Potential minus Mistakes equals Performance.

It would seem that both boats have similar Potential but the Italians make less mistakes in changes in boat calibration for the conditions and handling/tactical/positioning errors and have a better Performance.

The point that must always be remembered in these boats that a big lead is often more risky than a smaller lead, as with the smaller lead it is easier to stay in phase with trailing competitor, stay in phase with the breeze, and cover accordingly.

With a big lead it is too easy to both get out of phase with the breeze - in pressure and direction - and particularly downwind a big lead often creates a passing lane for rival, who has no option left but to gamble, and get lucky with breeze direction and or pressure. These races can turn inside out in the space of 30 secs if the lead boat gets split from the trailing boat, and then loses pressure/direction - comes off the foils, and sails at near zero VMG for even just 30 seconds.

The action resumes this weekend.

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