The Boats

Rainbow, the 1934 Defender

The America's Cup Regatta is sailed in America's Cup Class yachts, which were specifically developed for use in America's Cup competition. They were first used in San Diego in 1991 for the 28th America's Cup Regatta.

Great variation in the beginning
At the beginning of the Cup, restrictions imposed on the yachts had caused a great deal of variation in design. While the handicap of a 3000-mile ocean passage placed definite limitations on the challenger, all that was required of the defender was that she should hold together for her first season-a short-lived blaze of glory. In 1906 and 1907 a series of conferences were held, attended by representatives of 13 countries, including the three national classification societies then in existence. Following these conferences the International Yacht Racing Union introduced the first international rules for yacht measurement.

The great J-class yachts
During discussions leading up to the 1930 Cup races, which were to be held for the first time between the great J-Class yachts, it was decided that in the interests of the event, all vessels talking part in future Cup races would be built in accordance with same Rules. The revival of the contest after the Second World War was brought about by another alteration to the Deed of Gift - this time by the New York Supreme Court . This amendment reduced the waterline length to 44 feet and welcomed a new type of competitor to the races, the smaller 12-metre boats. The restriction that vessels had to sail across the Atlantic on their own bottoms had to be dropped.

New class prescription in 1990
The need for a new class prescription arose from two developments. The first was a growing disenchantment with the cumbersome 12-metre class, which had been used in the Cup since the first post-War event in 1958. The 1988 "mismatch" between the giant New Zealand sloop KZ1 and San Diego Yacht Club's catamaran defender also influenced Cup players, who determined to ensure that in future there would be a level playing field, and a new, more exciting class of yacht. This rule was established over a period of time during 1989 and 1990, with an informal group of designers sharing ideas, systemising the key parameters, and establishing new formula.

The ACC Rules
The 55 pages America's Cup Class Rules, known as the ACC Rules, are revised after each America's Cup Regatta and the fourth revision was used for the 31st America's Cup Regatta. The ACC Rules set stringent design criteria and establish a design formula which forces designers to balance length against sail area and displacement. Each yacht built anywhere in the world receives a consecutive class number.

Alinghi - Sui 75

Crew of 16 required
The America's Cup Regatta is now sailed in America's Cup Class yachts, which were specifically developed for use in America's Cup competition. Required to have 16 crew, they were first used in San Diego in 1992 for the 28th America's Cup Regatta. As it said in the AC Class Rules, "the America's Cup Class is intended to produce wholesome day sailing mono hulls of similar performance while fostering design developments that will flow through to the mainstream of yachting; and for yachts that are raced "around the buoys” with tenders present, as opposed to offshore in high winds and rough seas with or without tenders.”

Stringent design criteria
The ACC Rules set stringent design criteria and establish a design formula which forces designers to balance length against sail area and displacement. The variable geometry equation can be compared to a box into which the boat shall fit in, but inside which the parameters may be modified infinitely :

L is the rated length in metres,
S is the sail area, the sum of the fore-
triangle area and the mainsail area,
DSP is the displacement in cubic metres.

The problem consists of finding the best compromise beetween these three parameters in order to design and build the fastest ACC Yacht.


Inspection and measurement regimes
Average speed of ACC yachts from one edition to the next has progressed by something in the order of 3%, around 3/10th of a knots (0,54 Km/h) and, in order to won, you have to be 1% ahead of boats of the same generation. All competing yachts are subject to very stringent inspection and measurement regimes, both during construction and prior to and during the America's Cup Regatta. The ACC Rules are administered by a technical director and his staff who undertake inspections and issue interpretations of the ACC Rules from time to time.

Consecutive class numbers
Each yacht built receives a consecutive class number. When yachts change ownership, the sail number remains with the yacht, with only the national letters being changed if the new owner is of a different nationality. The class insignia is the silhouette of the America's Cup and appears on the mainsail.

More about the America's Cup