America's Cup 2013: Rules
AC72 Class Rule

CupInfo Home  |   2017 America's Cup: Teams  |  Results  |  Previous Events  |  Feature Articles  |  Books  |  CupStats

AC72 Class Rule

Related Pages: Overall Rules | Deed of Gift | Protocol | AC72 Class Rule | Racing Rules | Administration

On This Page: Box Rule | Minimum Weight | Interpreting and Certifying | Amendments | Read the Class Rule

  America's Cup Rules in Order of Precedence:

Click on chart to learn more:


Boats - The AC72 Rule:

The AC72 Class Rule was written to create a type of multihull catamaran expressly for the 2013 America's Cup.

The AC72 Class Rule sets out some basic constraints on size, configuration, materials, and construction methods, with the goal of allowing teams to seek faster and better yachts, advancing the state of the art.  At the same time, the Rule tries to guard against loopholes that might permit boats which possess extreme advantages via undesirable features.  Additionally, the Class Rule tries to prohibit certain material or construction techniques that add unnecessarily to expense, or which carry high risk of failure such as boron rigging.  The goal is sometimes expressed as "wholesome design," favoring the practical and useful that may benefit yacht design generally in the long run.

Class Rules, in the America's Cup and elsewhere, carry great implications for the teams, and receive intense scrutiny.  From the beginning, the America's Cup has been about innovation in yachting design and technology, a competition of designers and engineers as well as sailors pushed to excel, and having a rule that permits and rewards design development is intrinsic to the history of the event. 

Box Rule:
The AC72 Class Rule was intended to be more or less a "Box Rule," meaning that it establishes overall dimensions that may not be exceeded, but doesn't dictate the precise shape of the boat.  In spirit, a Box Rule means that as long as it fits inside the box, it can race.  This philosophy gives a lot of flexibility to the designers, without constraining too many aspects of the boat.  It also makes it possible that a clever design concept can produce a winning boat through innovation.  A Box Rule is in contrast to the approach of a formula-based rule, which at the other extreme often produces very similar boats that have to satisfy complicated system of measurements and calculations.

The AC72 Class Rule isn't a perfectly pure Box Rule, which taken literally might only mention length, beam, draft, and height.  In practice, very few Box Rule classes are actually that unlimited.  The AC72 Rule adds some basic configurations that the boat must possess, certain features that are required or prohibited, and limitations on the size and nature of major components.

back to top

Minimum Weights:

For example, where minimum weights are NOT specified for some components, a design team might end up spending enormous effort to continually reduce mass in one part of the boat, eliminating or relocating that mass to more advantageous parts of the boat.  In the previous America's Cup Class (ACC) monohulls, while there was an effective overall cap on weight of the boat, there was no separate requirement for weight of the hull alone versus the fin and keel below.  Under those rules, the pressure was always on to take weight out of the hull and make the lead keel heavier, which in turn kept the mast more stable and upright, and the sails more effective, resulting in a faster boat.  With no minimum weight for the hull, teams sometimes ended up with safety margins so narrow that unexpected loads or damage cracked the hulls, sinking OneAustralia in 1995 and breaking Young America in half, nearly sinking, in 2000.  The same scenario has played out historically regarding masts, with the J-Class in the 1930's eventually adopting a minimum mast weight to avoid the danger and expense of an epidemic of dismastings as the science of fabricating super-tall, but lightweight, aluminum rigs was being learned.

Even when boats don't break, if reasonable minimum weights or strengths aren't specified by rule then an inordinate amount of time and expense can be spent shaving off just a few more pounds, with quickly diminishing returns.  This situations is usually only to the advantage of the teams with the largest budgets and design staffs, and doesn't necessarily make the racing any more enjoyable.  The two Classes that preceded the ACC, the 12-meters from 1958-1987, and the J-Class, from 1930-1937, incorporated scantlings, a nautical term for specifying minimum sizing of hull structures.  Design effort was spent instead on the shape of the hull rather than obsessively minimizing weight in construction, and notably no America's Cup boats sank from structural failure in that era.

back to top

Interpreting and Applying the AC72 Class Rule:

Public Interpretations:
Yacht designers and engineers will encounter situations where proper reading and application of the Class Rule is critical.  Is a clever idea permitted within the rules or prohibited?  Is the Rule even understood correctly?  Rather than build what they think is best only to find out later that the boat does not conform to the Class Rule, teams are allowed to ask the Measuring Committee in writing for an interpretation of specific aspects of the rule.  Their questions, and the responses from the Measuring Committee, are confidential for 90 days, and then are published for all of the teams and the public to read.  Likewise, the Measurement Committee publishes documentation of methodologies that they will use to determine compliance, so that teams are prepared for the testing conditions. 

Both the Public Interpretations and Measuring Methodologies can be very detailed and technical, and are not usually easy to make sense of without intimate knowledge of the Class Rule and other documents, including previous interpretations.  More confusing, since the questions and answers will eventually become public, teams will sometimes try to phrase their questions to disguise the true nature of their interest, hoping not to tip others off to the ideas they may have discovered.  Or, to add another wrinkle, teams may sometimes ask a question hoping that the Measurers will respond in such a way that a design feature of a competitor is prohibited.  The Measurers sometimes appear compelled to point out, though, that even designs which skirt the letter of the Rules in question may still not satisfy the overall needs of the Class Rule, and not be in compliance.

Yacht Certificates:
Each AC72 yacht needs to receive a certificate that it complies with the Rule, in order to be able to race.  The Measurers conduct detailed tests on the boat to ensure each yacht's compliance, with the boat platform or wing in a specified measurement condition.  Any changes to the yacht that invalidate the certificate require re-measurement and an updated certificate before the boat can race again.  Section E (Rules 21-27) of the Class Rules address Measurement and Inspection, along with the Measuring Methodologies referenced above.  Appendix A of the Class Rule contains a sample blank AC72 Yacht Measurement Certificate.

back to top

Amending and Modifying the Class Rule:

The AC72 Class Rule was drafted by the firm of Morrelli & Melvin Design & Engineering, who have experience designing and racing large multihulls.  Successive iterations circulated to the Defender and Challenger of Record for review before eventual approval.  M&M divided their staff into two groups, one writing the Rule, and the other trying to find and eliminate loopholes in the Rule's language that defeated the intent.  The Class Rule was then approved by the Defender and Challenger of Record, first issued October 15, 2010.

Once adopted, modifying the AC72 Class Rule requires unanimous agreement among all current teams (excluding those eliminated in competition) and the Regatta Director.  This is in contrast to the Protocol, amendment of which does not require all teams to agree, only a majority plus the Defender and Challenger of Record.  Since the Class Rule cuts so directly to competitive balance, this provision is intended to prevent scenarios such as slower teams banning a competitor's faster design.  Additionally, the Measurers may amend the Class Rule for media requirements, and before March, 2011, the Measurers could amend the Rule without limitation.  Rule 4 of the AC72 Class Rule covers amendments.

Since adoption, the AC72 Class Rule has been modified 19 times as of August 31, 2013.  A few changes have been major, such as eliminating the option of a shorter wingsail.  Some changes are intended to clarify situations or improve language to remove ambiguity, while other changes are in relation to technical needs of the officials or broadcasters.  The changes of February 2011 created Version 1.1.  Subsequent changes have simply been categorized as amendments and not new versions.

back to top

Read the AC72 Class Rule:
including Amendments 1-18 (July 26, 2013):
Read AC72 Class Rule Amendment 1-18 (pdf)

Recent Versions and Amendments:
Read AC72 Class Rule Amendment 19 (pdf)

Earlier versions:

Click here to see All Previous Versions and Amendments to the AC72 Class Rule

Click here to hide the Previous Versions and Amendments

AC72 Class Rule: Versions and Amendments

Version:   Description: Date: Link:
Original   Version 1.0 15-Oct-10 Read (pdf)


1   Modifies wing measurement points; limits material strength; 31-Oct-10  
2   Created Version 1.1; 22-Feb-11 Read (pdf, 4.3MB)
3   Modifies wing measurement point; 27-Oct-11 Read (pdf)
4   Wing canting limitations; Measurement certificate; Stored power; Rigging language 24-Nov-11 Read (pdf)
5   Removable device for measurement of tack point; 1-Mar-12 Read (pdf)
6   Battens increased, changed; soft sail luff; 1-May-12 Read (pdf)
7   Media equipment; 12-Jun-12 Read (pdf)
8   Sail numbers and Class insignia; 2-Jul-12 Read (pdf)
9   Soft Sails; Luff attachment; 2-Aug-12 Read (pdf)
10   Cross-structure location; Netting; Soft-sail control; 6-Nov-12 Read (pdf)
        Cumulative 1-10 (pdf)
11   Crew Weight; Paint Systems; 4-Apr-13 Read (pdf)
12   Yacht Weight; Wing Weight; Floatation System; 8-Apr-13 Read (pdf)
13   Daggerboards not to increase Righting Moment; 9-May-13 Read (pdf)
14   Cross-structure 1m ahead of Stern Plane; 25-May-13 Read (pdf)
        Cumulative 1-14 (pdf)
15   Media Equipment; 14-Jun-13 Read (pdf)
    "Redline Markups": Safety Panel Recommendations added by the Regatta Director;  Note that these Recommendations as part of the Class Rule have been disallowed.  See note below; 28-Jun-13 Cumulative (pdf)
16   Wing measurement and CG changes; 03-Jul-13 Read (pdf)
17   No additional onboard video by teams; Changes in indicator light system; 17-Jul-13 Read (pdf)
18   Safety equipment; Transparent coverings; Limit of three softsails changed to two; 26-Jul-13 Read (pdf)
        Cumulative 1-18 (pdf)
19   Sailing weight increased by 10kg; 31-Aug-13 Read (pdf)

back to top


Other versions:
Read Redline Mark-up showing Changes to AC72 Class Rule by Regatta Director (pdf, 5.8MB)
Update, July 11, 2013
: The June 28 changes were issued by the Regatta Director to implement relevant aspects of the Safety Recommendations determined by the Review Panel following the Artemis Racing accident that killed Andrew Simpson on May 9.  While the AC72 Class Rule and the Protocol do not explicitly give the Regatta Director the power to make modifications to the Class Rule, it was stated by ACRM that the requirements were in the best interest of the regatta, and that the operative mechanism for enaction was the incorporation of the changes by attachment into the USCG Marine Event Permit (MEP) issued for the event.  Article 16 of the Protocol requires compliance with laws and regulations of authorities with jurisdiction, and ACRM appeared to take the position that the terms outlined in the MEP are thus binding on the teams.  Read ACRM Press Release

The teams were not unanimous in their support of the Class Rule revisions, with Emirates Team New Zealand objecting to changes in permitted rudder designs.  ETNZ withheld their consent to modifying the AC72 Class Rule, prompting the Regatta Director to take the action described above.  Emirates Team New Zealand and Luna Rossa disputed the change procedure by route of the MEP as not in keeping with the Protocol and the Class Rule, and protested the matter to the America's Cup Jury.  The Jury heard the protest July 8.  Read ETNZ and Luna Rossa Press Releases.  The Jury ruled on July 11 that the Regatta Director may not change the Class Rule via this method.  Thus, the redline mark-ups in this form were disallowed.

Why Have a Class Rule?
The America's Cup organization establishing their own Class Rule has two notable advantages. 

One, the boats are intended to be similar enough to race without time correction, as was early practice, so that the first boat across the line is also the winner.  This consideration helped prompt the adopting of the J-Class for the 1930 America's Cup. 

Two, because the Class Rule is created by the America's Cup teams and self-administered, it can be more responsive to the needs of the event.  The 12-Meter Rule, for example, used for the America's Cup from 1958 to 1987, was administered by outside authorities as part of the International Rule dating back to 1906 and involving many other boats.  Sometimes conflicts arose when the needs of Cup competitors and organizers were not aligned with the general sailing community. 

back to top

Additional Links and Info:

Visit Official America's Cup  website

CupInfo Home

Inquiries please contact: