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SailGP: Ainslie Incident - what the Umpires saw in the controversial Race 5 finish incident

by Richard Gladwell, 2 Aug 08:47 PDT 3 August 2022
What Ben Ainslie saw as he crossed Tom Slingsby's bow on Race Day 2 of the Great Britain Sail Grand Prix | Plymouth in Plymouth, England. 31st July . 2022 © Jon Super/SailGP

An incident close to the finish of Race 5 of SailGP Great Britain determined whether local hero Ben Ainslie or his nemesis Tom Slingsby (AUS) would go through to contest the Final in front of Ainslie's home crowd.

Umpire Booth animation and Ghost Boats view of the incident:

The challenging race was marked by significant variances in wind pressure across Plymouth Sound. In foiling terms, a variance of wind pressure in that wind strength (8-10kts) will often cause the F50s to come off the foils, particularly during tacks and gybes - with a massive reduction in boatspeed, let alone the time taken to get foiling again - while other competitors are foiling at speeds of 30kts plus.

In these conditions, the objective is to be precise with boat positioning on the course. In other words, the foiling wingsailed one design catamarans minimise their tacks and gybes, stay in good wind pressure to maintain foiling speeds, and optimise their sailing angle to sail the shortest distance. There are plenty of trade-offs to be made. The reputations of tacticians and flight controllers can be destroyed in an instant.

The third place in the Final devolved into a contest between the British and Australian teams, who made their final approaches to the finish line at the end of the second downwind leg (Leg 4).

Slingsby came in from the right-hand side of the course on starboard tack and holding right of way. But the wind angle and strength were insufficient for him to soak down to the finish line, and he would need to make one more gybe close to the finish to get across the line.

Ainslie, also initially on starboard tack, had made his move earlier, getting over to the left-hand side, and would have to gybe and then hope that he could negotiate a course across Slingsby's bow - which would assure him of the Final spot. Or, he could take the longer route behind the Australian, who has a reputation for seizing the opportunity to grab a vital place right at the death. Ainslie's second option, of passing astern of Slingsby, could mean that the Brits would have been forced to sail higher than desirable and might not be able to make a course for the finish line at a fast foiling speed.

Ainslie gybed and managed to stay foil borne.

Both competitors crossed the 300metre distance line with Ainslie almost a boat length ahead but travelling at 5.4kts slower (10km) out of the gybe. Maybe he was relieved to have got through the gybe and emerged out the other side still foil borne - and saw the flash of an opportunity to cross the Australians' bow and make the Final, despite being the port tack and give way boat.

Slingsby had set a classic match racing trap. Ainslie made a flash decision to take him on - in a moment of calculated risk.

The racing rules say that Australia, as the right-of-way boat, is not required to hold a steady course but tread a fine line in that they are not allowed to hunt down the give-way boat either.

The standard match racing response is for the right-of-way boat to soak down as close to the give-way boat's course and cut them off at the pass.

Suppose the Brits were going to be clear ahead, by a very narrow margin. In that case, the Australian's response is to put their bow up, claiming that the move was necessary to avoid a possibility of contact, as required of all right-of-way boats under racing Rule 14.

The same rule further requires that the avoiding action be taken only when the give-way yacht is not keeping clear. The backup ploy by the right-of-way boat (Slingsby) is to alter course slightly and appeal to the umpires for a penalty on the give-way boat (Ainslie).

In the Race 5 situation, Ainslie did accelerate out of his final gybe, and if he could quickly get back up to full speed, he looked to have a chance of getting across the bow of the Australian boat.

The downside of Ainslie's tactic is that he has to commit to cross ahead or behind, and if he chooses the former, Ainslie very quickly reaches the point of no return and is at Slingsby's mercy.

Slingsby turned about 10 degrees to windward when the two boats were closest together - claiming he had to alter course to avoid contact with the British.

The Umpires quickly agreed with the Australian requiring the Brits to pass astern - guaranteeing Slingsby the third place in the Final.

In the video, we have picked the essential segments of the broadcast video along with the view seen in the Umpiring Booth.

The final still frame is of the so-called "ghost boat" view, which is a projection for three boat lengths and discounting any course alteration by the right-of-way boat. The umpires would have been well aware of this projection before the two boats played out the intersection manoeuvre - and were able to make a quick decision.

Ben Ainslie's argument in the post-incident interview is that there was a big margin between the two boats at the course intersection - which the TV coverage shows - allowing for camera distortion. However, the question for the umpires is, "who created that extra room?" It is hard to argue that it wasn't a product of Slingsby's "avoiding" action, of which the standard practice is to "sell" this manoeuvre to the umpires as a necessary late avoiding action.

Given the high speeds and much higher closing speeds of the F50s sailing at 30kts and probably closing at 45kts, there is plenty of scope for argument as to likely outcomes. However, at those speeds, there is also a high risk of a collision if there is a miscalculation or crew error -particularly by the flight controller. Event organisers have made it clear they want to see less aggression after several major crashes at the end of Season 2.

  • To do your own analysis, use the wagon-wheel at the bottom of the Youtube screen to put the video below into slow motion (usually 0.25 speed) and watch the situation unfold, pausing at key points.

  • In the stern camera view on the Australian boat, you can also see Tom Slingsby make a subtle of the wheel, turning the bow up in an avoiding action - warranted or not.

  • You can sight the bow movement, which is very subtle but significant against the land in the backdrop.

  • In the overhead views in the TV coverage, you can see the boat wakes, the Australians soak low, and then alter course subtly to windward to claim an avoiding action.

  • You can also see the boat speeds at the time the British gybed and how these accelerated as they passed ahead of the Australians.

  • You can also gauge the relative separation between the boats by the "ladder lines" on the water, every 100 metres, which are radiused off the bottom mark/finish line.

  • Then compare your perspectives with the view the Umpires see in their Booth based on GPS positions of the boats and prediction algorithms.

The pressure was on the British to make the Home Final, which probably increases risk-taking in close finish situations such as in Race 5 on Sunday.

The solution is surely to give the Home Team an automatic entry into the Final, as in the America's Cup and Olympic Qualification. This change would allow the Home Team to race in front of their fans in the Final, give the event an authentic Finals atmosphere, and remove the natural tendency of the Home Team to take quite a high risk to secure that vital Final place.

For an earlier story, and more images

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