Statistics and Video Evidence: The Cost of Falling Off the Foils

America’s Cup: Insights into the Impact of Falling Off the Foils

Alinghi Red Bull Racing chases INEOS Britannia – Race 9 – Day 3 – Round Robin 1 – Louis Vuitton Cup – August 31, 2024 – Barcelona © Ian Roman / America’s Cup

Falling off the foils is a common risk in the current America’s Cup.

Recent analysis combining “black box” data and video footage from pre-start and racing moments provides valuable insights into how such incidents can affect race results. This is particularly crucial ahead of the Round Robin phase of the Louis Vuitton Cup, which is set to start in just over a week.

The “Black Box” data offers a comprehensive overview of the basic performance metrics collected on the boats during sailing. This data is accessible on the America’s Cup website for teams, media, and fans alike.

In our analysis, we focus on Race 9 between Alinghi Red Bull Racing and INEOS Britannia. There were two key incidents: the first occurred in the final seconds of the pre-start, and the second happened when INEOS Britannia attempted to gybe during their final approach, managing to escape with a lesser penalty.

Interestingly, the overall performance of both boats during this segment of racing was quite similar, suggesting that the race’s outcome is significantly influenced by each team’s ability to avoid mistakes. Unlike other high-performance sailing competitions, where all mistakes are considered equal, the consequences of falling off the foils can vary greatly.

To better understand this, watch the racing video and pause it at either 1:00 on the start countdown or 2:33 on the video. Notably, at 00:50, onboard Alinghi Red Bull Racing, INEOS Britannia can be seen completing a tack on Alinghi’s starboard bow. At 00:39, commentator Glen Ashby remarks, “I think they (Alinghi) might be off their foils.”

At 13:15 on the Speed Over Ground (SOG) vs Time graph, we observe Alinghi Red Bull Racing’s speed significantly declining as they approach the start line. Conversely, INEOS achieves a rapid speed build before tacking, reflected in a sharp dip in speed at approximately 13:18. It’s important to note that although Alinghi reaches a speed of 20.5 knots in the video, their Velocity Made Good (VMG) is only 0.7 knots, while INEOS is sailing at just under 14 knots VMG and has established a lead of 750 meters, which stretches to over 1000 meters after passing Mark 1.

The Altitude vs Time data indicates the duration above a base height (-1), which serves as the benchmark for determining whether the hull is clear of the water’s surface. The solid blue section represents the time Alinghi Red Bull Racing was off their foils, as confirmed by the SOG vs Time graph. At 13:40, we see INEOS also losing their foils as they approach the finish line. This situation mirrors what occurred with the Swiss team. It is crucial to remember that achieving higher speeds does not necessarily equate to meeting target VMG.

In the True Wind Speed (TWS) vs Time graph, we can see that during the prestart incident, INEOS Britannia is still sailing in clear air, while Alinghi is hindered by turbulent air emanating from INEOS, leading to suboptimal sailing conditions at recorded speeds of 4 knots. It takes about four minutes after Alinghi falls off their foils before they can recover from the turbulence affecting their performance. The overlap in SOG vs Time data between 13:20 and 13:37 for both teams indicates a minimal speed difference, but the crucial factor remains the VMG towards the next rounding mark.