America's Cup:
A Look at Recent Wind Limits

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Wind Limits, Why They Matter, and a Bit of History

June 10, 2013

  2013 Wind Limits:  
  Original Protocol Agreement (Sept 2010)
    2013 America's Cup and Louis Vuitton Cup:
3-33 knots
  After Amendment 15 (July 2012)
    America's Cup Match:
Louis Vuitton Cup Finals:
Other Louis Vuitton Cup:
5-33 knots
5-28 knots
5-25 knots
  Proposed: (May 2013)
20 knots
21 knots
23 knots
    (Adopted Amendment 18)  

Historical Wind Limits:
(Samples of the Rules from various America's Cup Matches)  Click on links or scroll down to read rule language.

J-Class Era 1930: Reasonable and practical.

12-Meter Era 1958 to 1980s:  Reasonable and practical.

2000: 5-18 kts to start, sustained 23 knots during race.

2007: At start 7 to 23 kts.

2010: 15 kts

2013: 3-33 knots, later modified.

From 1930 Conditions of the Match:

6. Postponements:

The time of the warning signal shall not be changed except as follows: [...]

c.  By the Race Committee if, in their opinion, the wind is so light or fickle that it is not practical to determine a windward or leeward course.

d.  If in the opinion of the Race Committee the weather shall be, at the time appointed for the start of any race, or threaten to be, of such severe character as not to afford a reasonable opportunity of fairly testing the speed of the two yachts, the race may be postponed in the discretion of the Race Committee.

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For NYYC 12-Meter Era: (similar language in Conditions of the Match from 1958 onward):

From 1980 Conditions of the Match

6. [...]


b.       If, in its opinion, at the time appointed for the warning signal, the starting area is not sufficiently clear or the wind is too variable or too light or too strong or the sea too rough reasonably to test the relative speed of the two yachts. [...]

The Race Committee may abandon a race as provided under Racing Rule 5.1(b) because of foul weather endangering the yachts or for other reasons directly affecting safety.

Under no circumstances may the course be shortened.

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 From 2000 Notice of Race

14.3 Before the Starting Signal the Race Committee shall postpone: [...]

(c) If in the starting area the true wind speed measured at 10 meters above sea level is continuously less than 5 knots; or if in the 15 minutes prior to the starting signal the wind speed is continuously greater than 18 knots for a period of 5 minutes. [...]

14.4 Before the Starting Signal, the Race Committee may postpone: [...]

(c) When in the opinion of the Race Committee the wind is too variable, or too light, or too strong, or the seas too rough, to reasonably conduct a race to test the relative speed of the two yachts. [...]

14.6 The Race Committee shall abandon a race after the Starting Signal during a Round Robin Series or the Semi-Final Series when the true wind speed is continuously greater than 23 knots for a period of 5 minutes measured at 10 metres above sea level.

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From 2007 Notice of Race (NOR): (similar for LVC)

10. WIND LIMITS The Race Committee intends to conduct races when the approximate average true wind speed is between 7 and 23 knots as measured on the Race Committee Signal Boat at six (6) metres above the water.

12.4 Before the Starting Signal, the Race Committee may postpone when, in its opinion: [...]

(b) on any part of the race course the wind is too variable, or too light, or too strong, or the seas too rough to conduct a race to reasonably test the relative speed of the yachts and  the skill of their crews.

12.5 After the Starting Signal, the Race Committee may abandon the race (display flag N, N over H, or N over A, with three sounds), as appropriate:  [...]

(b) because of foul weather;

[Note that 12.5 including (b) is essentially identical to the standard Racing Rules of Sailing Rule 32.1.]

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From 2010 Notice of Race (NOR):

 6.7 Wind and Wave Height Limits

To ensure the safety of competitors, officials and spectators, and taking into account the length of the courses to be sailed and the nature of the boats, RRS 27 and RRS 32 shall apply.  It is anticipated that races shall be sailed in winds having a windspeed of not more than 15 knots measured at 60 metres, and in waves of not more than 1 metre in height.

[Note that RRS 27 allows the RC to abandon before the start for any reason, and RRS 32 is similar 12.5 quoted above, allowing abandonment after the start for foul weather.  Also, there were previous, sometimes disputed, variations in the 2010 Rules. This are the version that finally prevailed.]

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From 2013 Protocol Article 21.1

Original (September 2010):

21.1 Competitors are required to race in all regattas of the Event for which they are eligible. Unless the Race Officer considers conditions too rough, the race committee intends to start races when the approximate average true wind speed is between 3 and 33 knots as measured on the race committee signal boat at 6m above the water.

Per Amendment 15 (July 2012):

Competitors are required to race in all regattas of the Event in which they are eligible.  Unless the principal race officer considers conditions too rough, the race committee intends to starts races when the approximate average true windspeed is between:

(a)   5 and 33 knots for the AC World Series and the Match;

(b)   5 and 28 knots for the ACCS Final; and

(c)   5 to 25 knots for the balance of the ACCS;

Measured as a rolling (box-car) average of one hertz samples over 60 seconds using a Gill wind-sonic on the race committee signal boat at 1m above the water.

Proposed/Pending (from Draft Recommendations (May 22, 2013) (Update: Adopted in Amendment 18):

4.4. Wind Limits: Reduced to 20kts in July, 21kts in August, and 23kts in September (as measured pursuant to art. 21.1), but with additional wind limit adjustments for tide and sea state.

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For the 2013 America's Cup, the wind limits were initially set in order to provide a high likelihood of racing over a wide range of conditions.  Many recent matches involved delays of several days at a time when conditions were deemed either too light, too variable, or too strong to begin racing.  A growing number of fans, sailors, and competitors were disappointed to see some of the world's most advanced racing boats and talented sailors heading back to shore for a postponement in the same conditions that are usually considered enjoyable and manageable for many amateurs, even teenagers.

Likewise some of the most memorable television images in America's Cup history came from Fremantle, Australia, where strong daily breezes and significant waves made for compelling visuals in the 1986-87 Louis Vuitton Cup and America's Cup.

In the 12-meter era and before, explicit wind limits were not established.  The decision to race or not was left up to the judgment of the Race Committee, with the general criteria focused on whether the conditions would offer a fair test of speed between the two yachts in the match.

Although setting out an explicit wind range in the regatta documents serves to counter accusations that the Race Committee is deciding whether to race based on a bias for the Defender, and stating a hard number has a sense of fairness in that both defender and challenger(s) have agreed to the specifics or at least agreed to the process for setting the limits, in practice that hasn't stopped one side or another from voicing complaints when it suits their purpose.

For many years, the rules regarding acceptable conditions for racing were set out in the Conditions of the Match, a documented accepted by both Challenger and Defender.  In recent years, the wind limits were named in the Notice of Race, a document issued under the authority of the Protocol agreement, with various degrees of control and independence relative to the challengers and the defending yacht club as to the terms.  For 2013, the wind limits are stated in the Protocol itself, with changes via an amendment that requires a majority of the teams and the Defender and Challenger of Record to agree.

In Practice:

With the advent of the America's Cup Class, the yacht class used in the America's Cup from 1992-2007, specific ranges were set in the Notice of Race, though notably several times important races were not started owing to variability of wind direction rather than just lack of wind strength.  Predictably a team that perceived they had an advantage over the other in light conditions was quick to criticize the RC's decision to race.  Viewers of live television in 2003 heard some choice words from the challenger's boat in this regard when the RC chose not to start.  Members of the same team were livid in 2007 when, as defender, a race was started in light air conditions and they went on to lose.

More notoriously, in the 2010 America's Cup, a head-to-head Deed of Gift Match, the Defender tried to build a boat that excelled in very light wind, and also attempted to select a racing venue to deliver those conditions, in the hope that they could find a weakness in the performance profile of the challenger's boat.  In the end this scheme wasn't quite achieved, despite a disappointing scene in which the defender's race committee members, not believing the conditions light enough to be to their advantage, did not assist the independent Principal Race Officer in starting the race.  The race was started anyway, with the Challenger winning the decisive race and clinching the Cup.

Wind Limits are a Critical Design Factor

Even when administered fairly, though, the setting of wind limits is a critical parameter for the design teams from the first blank sheet of paper until the last race is over.  Designing a boat that performs well within a narrow range is a much easier task than designing one that has to compete across a broad range.  The design teams extensively model the expected race conditions and make detailed trade-offs to balance performance in the predicted wind ranges.  A boat that has to hold up while racing in 20-25 knots versus 25-30 knots or over 30 knots will be created around different forces, structural loads, and dynamic effects.   Likewise testing will concentrate on verifying the expected loads and looking for weaknesses in those conditions.  The sail plans and the crew techniques that evolve in training also will take into account in the expected race conditions.

With the design process beginning nearly 3 years before the match, and the entire multi-million dollar development program focused on preparing for the circumstance of the Match and the Selection Series, the teams have to consider the probabilities and commit their resources accordingly.  Do you build a good all-around boat that excels in no particular race situation, or a boat that emphasizes one part of the wind range at the expense of another?  The America's Cup has been won and lost before on just such calculated trade-offs.

Changing the wind limits, or any other major element of the race conditions, even with the best of intentions can change the competitive balance of the racing. 

Controversy is Where You Find It

Historically, the sailing conditions and the decision to start a race or not have usually not been a primary point of controversy, though there have been exceptions. 

The lower wind limit was rarely an issue in the early history of the America's Cup.  Races were started in light winds and if neither boat finished within the time limit, then the race was abandoned.  In the last 20 years or so, television became an increasing factor, with pressure to provide a race to viewers on schedule, and in the same period the match moved to venues that were capable of providing light and fickle breeze such as San Diego, Auckland, and Valencia, leading to several races in the LVC, and occasionally the America's Cup itself, where luck in the "wind lottery" appeared to play at least as great a role as sailing skill.  The racing in these conditions was underwhelming as a spectator sport, and for supporters and sailors frustrating after years of build-up to have the outcome decided nearly by chance.

At times the higher end of the scale has come into play.  In 1920, the intended 5th Race of the America's Cup, to be staged on the "Outside Course" in the open Atlantic Ocean between defender Resolute and challenger Shamrock IV, was not sailed due to high wind and waves.  Conditions before 9:00 am in the harbor were said to be already 30 knots.  The press and some of the public were quick to castigate the NYYC, taking the position that Shamrock IV, having lost light air races, would fare better against the defender Resolute when the wind was high.  So the accusation was the race had been unfairly called off to aid the defender. 

Like many past America's Cup controversies, that wisdom was handed down in certain channels very receptive to such an interpretation.  That the postponement was a partisan decision was vigorously disputed by Sherman Hoyt, the NYYC representative onboard Shamrock IV, pointing out in his autobiography that the tug which was supposed to set the windward mark and log the positions and rounding times of the racers could not get upwind to set the mark, and that the boat with the press aboard had not even left the outer harbor.  Hoyt does say that the boats could probably have completed the course without serious damage, but that they weren't really fit for the weather and the sailors seemed relived not to have to attempt it.

One of the more dramatic America's Cup races was the third of the 1893 match, defender Vigilant taking on challenger Valkryie II in over 30 knots of wind with Vigilant's 70-man crew flying spinnaker, balloon jib, and a topsail over her enormous main.  50,000 people in the spectator fleet watched as Valkrie's crew tried to match the defender, shredding two spinnakers in the process, yet only losing by 40 seconds on corrected time, the closest margin of any America's Cup race to that point.   This was the first America's Cup contested in the "Big Class" yachts which would dominate racing for the next few decades.  With lengths overall that would exceed 120-130 feet, displacements nearing 150 tons, and 10-12,000 sf of sail area, the boats of the era have been described as "complicated, fast, fragile, and expensive" by historian John Rousmaniere.  The 1893 match was controversial for other reasons, but despite the difficult sailing conditions complaints did not focus on the wind limits.

Moving the Guardrails

Wind limits for the 2013 America's Cup have become controversial because the act of changing the limits, and what they are changed to, has the potential to alter the competitive balance between the teams.

The death of Andrew Simpson is a scene that nobody would want to ever see repeated in the America's Cup, and the safety precautions have to be considered in setting race conditions.  The Regatta Director still has substantial authority to determine when racing should or should not take place, regardless of any hard numbers that have been stated in the Protocol.

The AC72s are generally regarded as "overpowered" in the upper end of the initial wind range, over 25 knots or more by some team members.   But the term "overpowered" doesn't mean the boats are inherently unsafe, just that they reach a zone where the sails are no longer trimmed for achieving maximum lift at minimum drag.  In higher winds, sailing fast involves depowering the wing, and flying smaller soft sails upfront, to avoid too much heeling angle.  Catamarans are fast when they are slightly flying their windward hull, and too great of heeling angle is slower and more awkward than the optimum angle.  Photogenic sometimes, but slower.

In a soft sail catamaran, one technique to depower the boat is to decrease tension of the mainsail leech, the rear edge of the sail.  The shape of the sail will take on a twisted shape, normally undesirable because it is inefficient, but useful in high winds for the same reason.  Reducing lift in that situation means a flatter, faster, and more stable boat.  The hard wing of an AC72 can't twist off in exactly the same manner as a soft sail, but individual flaps of the wing can be angled to produce lower amounts of lift.  ETNZ has actually been able to trim their upper wing flaps in what would normally be the "wrong" direction and produce a righting moment, providing a force opposite to the normal lift vector, and helping to bring the boat back level.  Surprising at first, but much in the way that a wing functions in aviation, too.

The original intent when the AC72 rule was created in 2010 was to have multiple hard wings, one of the current size (40m/131 ft), one of a shorter size (32m/107 ft), which could be selected by the Race Management organization according to conditions.  The AC72 Class Rule was written and put into effect with that provision.  This arrangement was chosen in preference to having a single shorter wing with an added panel on top, as used for the smaller AC45 boats in the ACWS.  Though the concept was adopted, the plan for two AC72 wing sizes ran into opposition on several fronts.  A number of teams were concerned about the added cost and complexity in designing and engineering for two wing heights.  On the practical front there was the question of how on a daily basis the choice of wing size would be made, and the logistics of having several teams get access to the crane each morning to swap the wing masts in time for racing.  Possibly the issues could have been worked out, but at the time coping with multiple sizes of wings was a complexity that consensus of entered and prospective teams did not favor.  In February, 2011, the AC72 Rule was modified to eliminate the smaller wing size. 

That decision of course led the teams to design boats with only one wing size to face the stated wind range.  ETNZ launched earliest, testing and developing a boat that eventually they let loose in very strong winds, appearing stable and under control.  Luna Rossa's boat is a nearly identical design to ETNZ boat #1.  Oracle had the spectacular capsize of their first boat, with resulting damage, after 8 days of sailing.  Artemis Racing sailed for 36 days before their tragic accident.  Oracle's capsize came in winds that were strong, but within the wind limits of the Protocol, at least as reported, and Artemis was sailing in conditions that reliable sources report as lower 20 kts with gusts into the low 30s.  The exact reason for the Artemis accident has yet to be determined.  It's not clear that lower wind limits alone would have prevented either of the AC72 capsizes to date.  The concern of some sailors, however, is that much is unfamiliar about the boats, and reliable techniques for managing them and depowering when conditions become potentially overwhelming are still being developed.

A question of fairness arises, since from ETNZ's perspective, the Kiwi team developed boats they feel are manageable in the conditions that were in effect when they entered the regatta and began to design their boat.  Oracle and Artemis made different design decisions, which some observers believe led to boats that become vulnerable to capsize in rising windspeeds earlier than ETNZ and Luna Rossa.  The perception for some is that the Oracle and Artemis boats are optimized for lower winds, and disadvantaged against ETNZ and LR in higher winds, and that race conditions are being changed to suit two of the competitors at the expense of the others.  Yet, in fairness, it has to be noted that Luna Rossa Chairman Patrizio Bertelli has been one of the most vocal in calling for much lower limits following the Artemis accident, backed by his sailors.

Likewise, it's not just the the boats are large, fast, and highly technical to sail, but also that the time on the water has not been as extensive as originally planned.  The first date to launch an AC72 was supposed to have been January 1, 2012, with the boats beginning to compete in August 2012 in San Francisco.  This timeline was probably aggressive considering the design task, and again there was a call from the entered and prospective teams to modify the dates specified in the rules, reduce cost, and increase available design and build time.  By agreement, the Protocol was modified and the first AC72 launches were pushed back to July 1, 2012.  As it turned out, only ETNZ even came close to the new July launch date.

In the tradition of unintended consequences, though, the loss was six months or more of time, and attendant early experience with the AC72's that would have been accumulated.  The goal was admirable, making the event more achievable for teams across the budget spectrum.  And regardless of launch dates, even high budget teams like Artemis and Oracle have been unable take full advantage of the modified sailing dates.  Had the dates not been changed, would the teams have adjusted their programs and been ready, or were the original timelines unrealistic?  A lot of elements of the 2013 America's Cup are unprecedented, and this question will have to remain unanswered.

Of course, even before the launch dates were slipped back to July, 2012, the Restricted AC72 Sailing Periods were from the first intended to be limited to 30 days and then 45 days, so how much more early experience would have been gained?  On the other hand, had the dates not changed, there would be two or three AC72 regattas already completed.  The sailing limitation was instituted again in the interest of controlling costs and leveling the playing field between lower and higher budget teams.  In the end did the restrictions lower costs?  Did they affect safety by limiting sailing?  Consequences of such rules are hard to predict.

The reality in June 2013 is probably that the boats need to be reasonably safe, and even if the risks of injury in capsize can be sufficiently managed with safety precautions, that the damage from a capsize incident is capable of eliminating a team from competition.  Wind limits can't be changed without inherently favoring one team over another, no matter the best of intentions, and regardless of the class of boat, even.  "How low is safe?" is another unanswerable question.  Or safe enough.

--From Davis/2013 CupInfo

Links of Interest:
Part Two of our discussion with Pete Melvin reviews some of the decision-making process on wing size.

See AC72 Launching and Sailing dates for Restricted Period compared for each team.

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