The regatta course for the America's Cup races is laid out anew every day. The races are scheduled to last between 20 and 25 minutes, with the length of the course varying depending on the wind strength and direction. The course is limited on all sides, the limits may not be sailed over. Reaching a limit is indicated on board by light signals. The affected cat must then tack or jibe.
This battle between Emirates Team New Zealand and Land Rover BAR, which ends in a crash, shows just how hot things can get in the pre-start phase
The course in detail
Every race begins with the pre-start skirmish for the best starting position. This depends on the position of the line in relation to the wind. Unlike normal sailing regattas, the races do not begin with an upwind course, but with a slightly more spacious half-wind course. They then go round the first mark on a downwind course. Downwind there is a gate consisting of two marks that must be sailed through from above. The teams are then free to round the left or right mark. This gate has also become established in normal races because it gives a boat that is behind, i.e. attacking, the opportunity to choose a different course to that of the opponent ahead and not simply sail after them. This creates more tactically interesting situations and more overtaking opportunities.
After the gate, the course goes upwind, which again ends with a gate to windward, where the same applies as at the leeward gate. This is followed by another downwind course, the leeward gate again and finally a room sheet course to the finish. The number of laps may vary depending on the wind.
The right position at the start
Normally, the leeward position is desired at the start. From this position, the cat can be luffed to windward because it has to keep clear. If everything is right, the helmsman of the leeward boat can force the windward boat to make a hard windward manoeuvre before the start, which often means a touchdown, falling off the foils and thus a great loss of speed. In addition, from this position the leeward boat can determine the time at which it drops off again after a windward manoeuvre and picks up speed. The upwind opponent can only react to this, so will pick up speed later and lose metres. However, this all requires good timing from the team on the leeward boat.
The leeward position at the start has another advantage. On the way to the first mark, the catamaran upwind has to keep clear of the one downwind, so always be prepared for a manoeuvre by the opponent. It will therefore always sail a little higher than the direct and therefore shortest route that the leeward boat can choose. If the windward boat is faster, it cannot fully exploit this advantage and sail over the leeward boat, as the latter can defend itself with a windward manoeuvre to which the windward boat must react.
Even if the windward boat is slower, it has to take the slightly longer route to windward of the leeward boat's course - because the modern AC-50 boats cannot sail directly behind each other. The boat astern would then be caught with its foils in the turbulent water of the boat ahead. As the current foils are very unstable anyway, this turbulent water could lead to a crash.
If both boats start at the same time and are travelling at the same speed, the leeward position on reaching the first mark guarantees the inside position when dropping to the downwind course. The leeward boat is free to choose when to drop, while the windward boat, as it has to keep clear, will always drop a little later and thus sail additional metres, as it can only react to the leeward boat's dropping manoeuvre.
The sometimes action-packed skirmish before the start is usually aimed at reaching the inside position, i.e. the left side of the line, and pushing the opponent to the right.
Groupama Team France explains the rule here in a somewhat curious but understandable way (French)
Left can also be dangerous
However, the leeward position is not always automatically the better one. This also depends on the position of the line in relation to the wind. For example, if the right-hand start line buoy is slightly more towards the first mark, the boat upwind already has a few metres advantage, even if both start at the same time. There is then a risk of the leeward boat being overrun to windward, which should be avoided at all costs. This should be avoided at all costs, as it would get caught in the cover of the windward boat and lose many metres.
For this reason, in addition to the advantages mentioned, the leeward start also has a major potential disadvantage. Even if the line is exactly at right angles to the course to the first mark, i.e. neither windward nor leeward are favoured from the path, a slightly delayed start of two or three seconds is enough for the windward boat to overrun and be covered. The windward boat, on the other hand, can afford a slightly delayed start. Although it will then be behind, it will not lose any additional metres due to being covered and a possible touchdown.
Which foil is the right one?
As previously explained, the foils are of particular importance in this cup. Only four foils are allowed, but which are the right ones? It would be easy to have two sets, one for light winds and one for strong winds. However, it is also conceivable that some teams will enter the race with asymmetric equipment, i.e. with different foils in each hull.
For example, a superior foil on the port side, especially on half-wind courses, would be conceivable in order to leave the opponent standing on the all-important first section from the start to the first mark and then only have to defend.
The other foil, on the other hand, could have more of an advantage on the upwind course, as the statistics show that there have been no changes in position on the last half- to full-wind course to the finish so far. A half-wind foil would therefore not be so important there.
In this configuration, however, a cat would be at a disadvantage on the upwind course, at least on one bow, the one with the half-wind foil. However, as the Cup will most likely be decided on the upwind course, there is little to be said in favour of an asymmetric configuration.
The important upwind course
Softbank Team Japan shows the foiled turn, a novelty at this Cup and a reason why the upwind course is gaining in importance
The tacking angle of an AC 50 is between 100 and 110 degrees, the jibing angle is 90 degrees. As the race course is limited all round and these limits must not be crossed, the boats have to tack more often on the upwind course than they have to jibe on the downwind course. Downwind, they do not reach the limits as often due to the better jibe angle. Although the downwind part of a race is higher than the upwind part because the start is upwind and the finish is downwind, it is easier to convert a small speed advantage into a lead and defend it than downwind. The races are therefore very likely to be decided on the cross.
The right weather forecast
As always in sailing, an accurate prediction can decide who wins the America's Cup. As the twist of the sash is already set on land the team needs to know in advance how much wind, how many waves and what vertical temperature distribution is to be expected in the air. The choice of the right foils also depends on the wind.
However, unlike in previous cups, the teams are not allowed to take their own wind and temperature measurements. They receive the data from the regatta organisers and can derive their own forecasts from it. The trick is therefore no longer to collect data as accurately as possible, but to draw the right conclusions from the available figures and develop the right forecasting models. Defender Oracle Team USA, for example, has worked closely with Airbus on this.
Together with Airbus, Oracle Team USA has developed its own model for wind analysis and forecasting
The big Cup guide: In the America's Cup special in YACHT 12/2017 you will find all the information and background to the sailing event of the year. From 24 May at newsagents or digital here.
Lars Bolle
Chief Editor Digital
