America's Cup: 7 things to look out for during racing

Finally! The racing is about to begin in the 35th America's Cup. Mark Orams, NZME's resident 'racing professor', details what to look out for over the next month.

1. Key decisions before the race:
Every day, each team will be closely examining the wind forecast for the racing period as they will need to configure their yacht with the best set up to match the expected conditions. There are a range of options available to the teams, the most critical of which is the choice of the main foils they place on their yacht for the day. Each team is permitted to have two sets (pairs) of main foils and the general consensus is that they will have optimised one set for light winds and one set for stronger winds. Light wind optimised foils will be designed to have higher lift to ensure the yachts stay up 'flying', because this is much more difficult in lower wind-speeds. The trade-off is that higher-lift foils are also higher-drag foils and this means in higher wind speeds they are slower. Thus, teams will need to make a key decision before leaving the dock based on the expected wind speed and when the wind speed is in the cross-over range for the light and strong wind foils that decision may be a race winner or loser.

An additional consideration is crew weight. This America's Cup permits a maximum crew weight of 525 kg. Having close to the maximum is an advantage in strong winds. However, in lighter winds where the yachts may be marginal in their ability to fly on the foils, it is better to sail with a lighter overall crew weight to promote flight. The rules allow teams to change up to two crew members each race, so teams can potentially swap out a grinder (or 'cyclor') who might weigh 95 kg with one who weighs 85 kg if the wind is light and conditions are marginal for flying.

2.Pre-start manevoures:
The pre-start is the time when the yachts enter the "box" (the area below the start-line) and can work against one another to gain advantage either via the rules or via a positional advantage off the start-line. In this Cup the yachts enter the pre-start with only 3 minutes to go before the start. Given the speed these AC50s travel at, there is very limited time to try and gain an advantage. Typically the team that feels they are faster than their opponent will seek to minimise risk of a rules transgression and subsequent penalty from the jury. The team who feels they are slower will try to engage more aggressively and may be prepared to take higher risk options. To date, in practice racing, teams have fought to win the "pin" end of the start-line. This is the end of the start-line that is further away from the direction the wind is coming (called "leeward" in sailing terminology). The advantage this provides is that under the rules of sailing the yacht closer to the direction the wind is coming from (called "windward" in sailing terminology) must give way to the yacht to leeward. This means the yacht at the "pin" end of the start-line has the ability to control the yacht which is to windward. A further advantage is that the yacht to leeward has the right of way around the first mark on the course - so unless the windward yacht can overtake the yacht to leeward and be clear ahead - the leeward yacht has the right of way to turn first and lead around the first mark.

3.Foil down stability risk:
In watching the practice racing what became clear is that a key time of instability for these new full-foiling yachts is when they drop their windward foil (which is retracted for speed purposes when sailing in a straight line) in preparation for a maneuvor. When this retracted foil is deployed and hits the water if the angle of attack (the angle the foil is presented to the water flow) is slightly out the yacht can crash down or rear-up suddenly. This can result in a big-nose dive or "bunny-hop" of the yacht which is both dangerous and slow. The better teams seem to be managing this risk well, but it remains a risk. These yachts travel so quickly that any 'crash' off the foils onto the water surface is slow and the opponent can gain a large distance.

4. Splits at bottom and top mark gates:
The race-course configuration has turning marks at the top and bottom of the course which has a "gate", that is, two marks set at 90 degrees to the wind direction. The yachts can choose which mark to turn around. This provides an overtaking opportunity for the trailing yacht who will most frequently choose the opposite mark to the leading yacht. This immediately creates a split in the area of the course the yachts are sailing in creating the chance that the trailing yacht finds some extra wind or different conditions allowing them to pass the leading yacht.

5.Touch-downs, falling off the foils:
When watching the practice racing an area I observed when many of the yachts seem to struggle is turning around the bottom mark to head upwind. The boats are travelling very fast at this point of the race, likely in excess of 45 knots. As they turn upwind they slow-down and, as a consequence, many drop their bow (nose of the yacht) into the water and some fall of their foils completely. This results in a big loss of speed and the yacht loses ground to their opponent quickly. This loss is compounded by the need to turn away from the wind (and therefore away from the next mark they are racing to) to generate enough board-speed to climb back up onto the foils. Not good!

6. Breakages:
It's an old adage in sailing; "to finish first, first you must finish". These yachts are travelling very fast and the loads on the equipment are huge. Breakages and break-downs will happen and if a yacht is unable to finish they score 0. In addition, if the breakage is serious enough that they are unable to compete for the rest of that day, they lose all subsequent races and their opponent if they are able to complete the race takes the point. So, potentially if a yacht has a major breakage in the first race of the day and they are scheduled for two races that day it is two points lost and easy points for their opponents.

7. Improvements:
If we learned nothing else from the result in San Francisco four years ago we learned that it is never over until it is over! This 2017 America's Cup regatta will be a month in duration and the team that wins will be the team that improves the most over that time. None of the six teams are sailing at their full potential with these new AC50s yet. Developing performance across all aspects of the team, including speed, maneuvorability, reliability, decision-making, continuing to develop and perform under pressure..