12-metre class

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Contents 1 Introduction 2 The Formula and Rules 2.1 First Rating Rule 2.2 Second Rating Rule 2.3 Third Rating Rule 2.4 Third Rating Rule - America's Cup Rule 3 America's Cup 3.1 Famous 12-metre Yachts - America's Cup Era 4 Post America's Cup 5 External links

[edit] Introduction

The 12-metre class is a group of sailing vessels which, while not identical, are all designed to a particular formula, so as to make the boats involved in a competition roughly comparable, while still giving individuals the freedom to experiment with the details of their designs. The first 12-metres were built in 1907 and the last in 1987. The 12-metre class was used in the Olympic Games of 1908, 1912 and 1920 but are probably best known for their use from 1958 to 1987 in the America's Cup.

Rough equality between boats is ensured by requiring compliance with a formula that takes into account the length at the waterline, the girth (the measurement around the boat from one sideboard, under the keel and then back over the top on the opposite side back to the original side) and the sail area. The very carefully specified measurements are then entered into the formula, and the result must be 12 metres - hence the name of the class. Designers are free to change any of these variables (as well as other details, such as the size of the rudder and keel, etc), with the understanding that for any change in any of the measured attributes, something else will have to be adjusted, in order to make the formula produce the required value.

The "12-metre" in the class name thus has nothing to do with the actual length of the boats, which ranged from 65 to 75 feet (about 20 to 23 m) overall. They were all sloop-rigged, with their masts typically being about 85 feet (26 m) tall.

[edit] The Formula and Rules

The Formula and associated rules for designing and constructing 12-metre yachts has been modified several times from inception in 1907 through to the post WW II years when the 12-metre became the class for America's Cup racing.

The purpose of the Formula and rules was to encourage designer creativity to optimise designs to get the best overall performance when racing whilst maintaining competitive racing between the different designs. Although the Formula and Rules allowed some creativity they were also intended to be comprehensive enough to eliminate loop holes which could result in an extreme design which conformed to the 12-metre rule but completely outclassed other contemporary designs on the race course. If the rules were considered to be too loose then it would discourage the building of new 12-metre yachts for fear of a new boat being outclassed even before it was launched.

The Rules were typically updated in response to advances in areas such as material technology (eg Metal masts versus wooden masts etc), design technology (eg use of the wind tunnel to design sails and sail/mast combinations, advances in fluid dynamics etc), equipment (eg winch technology etc)

The Rule has four distinct periods:-

[edit] First Rating Rule

Used from 1907-1920

where

• L = waterline length (LWL)
• B = beam
• G = chain girth
• d = difference between girth and chain
• S = sail area
• F = freeboard

[edit] Second Rating Rule

Used from 1920-1933.

where

• L = waterline length (LWL)
• G = chain girth
• d = difference between girth and chain
• S = sail area
• F = freeboard

[edit] Third Rating Rule

Used from 1933 –1939.

where

• L = waterline length (LWL)
• d = difference between girth and chain
• S = sail area
• F = freeboard

[edit] Third Rating Rule - America's Cup Rule

Used from 1956 onwards:-

(International Twelve Metre Association):

where

• L = waterline length (LWL)
• d = difference between girth and chain
• S = sail area
• F = freeboard

Associated with the formula is an extremely comprehensive set of rules. The rules can be classified into two main areas. Rules concerning safety and rules to ensure competitive racing. For example the maximum total area of all cockpits is specified to minimise the chance of a boat being swamped in rougher seas. Structual requirements are specifies to ensure that strength is not sacrificed by the need to get weight low down in the keel. Materials are specified plus numerous other details concerning all aspects of the boat. The intention is to challenge designers but ensure competitive racing.

[edit] America's Cup

When America's Cup racing resumed in 1958 after World War II, more economical vessels were desired to replace the huge and expensive J-class yachts that were raced in the 1930s; the 12-metre class was selected. In 1987, use of the 12-metre class was ended, switching to International America's Cup Class boats for the 1992 competition.

[edit] Famous 12-metre Yachts - America's Cup Era

• Australia II won the America's Cup in 1983 which was the first time that the USA had lost the trophy in over 100 years. Australia II designed by Ben Lexcen was one of the first racing yachts to use appendages/fins on the keel which made the yacht more manoeverable. The keel design allowed a reduction in weight in the keel which then allowed other beneficial changes in the measured dimensions which resulted in a yacht optimized for the conditions on the race course in Newport Rhode Island.
• Courageous Designed by Olin Stephens in 1974 and one of two only boats to successfully defended the America's Cup twice.
• Intrepid Designed by Olin Stephens in 1967 and one of only two yachts to successfully defended the America's Cup twice. Intrepid is also famous for design innovations such as a revised rudder and keel configuration which became the norm for future 12-metre designs.
• Vim Designed in 1939 by Olin Stephens who considered the possibilities given by every aspect of the rules and produced a very fast boat. Vim had numerous innovative features including a trim tab on the rudder, two-speed winches and a lighter mast made made of duralamin (a form of aluminium used in the aircraft industry). Vim is considered a benchmark design which was continually refined over her racing career. In 1939 Vim came to the UK and won 19 races out of 28. The next generations of 12-metres designed and built 20 years after Vim was launched still found Vim extremly difficult to beat in competition.

In addition to design there are other factors which affect racing results. There are other 12-metre designs which are fast boats but struggled to reach their full potential due to inadequate crewing or lack of preparation or bad luck or a combination of both. In the America's Cup era it will always be a matter of debate but Australia II, Intrepid and Vim are generally considered to be the best 12-metres in terms of design excellence and performance on the race course.

[edit] Post America's Cup

12-metre yachts were used for the last time in America’s Cup competition at the 1987 event held in Freemantle, Australia. 12-metres continued to race together on a local basis but due to the high cost and without the impetus and prestige surrounding competition in the America’s Cup, no new boats have been built since 1987.

The latter part of the 20th century saw a big revival in interest in classic yachts including 12-metre yachts and particularly those of wooden construction. There were an increasing number of prestigeous regattas in attractive locations such as the Mediterranean and the Carribean. Also a more prosperous global economy prevailed and the result was an increasing number of restorations and racing of older ‘classic’ 12-metres.

Potential restorers of older boats who wanted to race were potentially faced with a dilema of whether to restore a boat to its original specification or make modifications to make an older design competitive with a newer design. For example a yacht designed under the First International Rule would have a wooden mast, gaff rig and sails made of cotton whereas Vim designed under the Third International Rule had a metal mast, bermudan rig and sails made from Dacron.

To encourage participation in racing and also encourage restoration which remained true to the spirit of the original design, the 12-metre class association introduced a handicapping system to allow 12-metres of all ages to race together on a more equal footing. The basis is a handicap applied to each boat according to the ‘era’ of its design to encourage owners to restore older boats and participate in exciting and sociable racing.

A 12-metre is classified as belonging to one of three periods. Each Period is defined as a range of dates which coincided with a particular type of keel or rudder design becoming widespread.

Period A:- Starts when winged keels became the norm. It covers all yachts built with winged keels and all yachts constructed after 1983. Australia II is the only wing keeled 12-metre constructed before 1984 and is in Period A.

Period B:- Starts when a skeg mounted rudder separated from the keel became the norm. It includes all 12-metres built during the period 1968 - 1983. It also includes Intrepid built in 1967 which first introduced a skeg mounted rudder. It excludes Australia II built in 1982 which is in Period A due to its winged keel design.

Period C:- All other 12 metre class yachts built before 1968 but excluding Intrepid which is in Period B by virtue of its skeg mounted rudder design. Period C has 7 sub classes primarily related to the year of construction of the boat.

In the early 21st century interest in ownership and restoration of 12-metres was such that specialist restoration companies would speculatively locate old boats under threat of destruction and publicize the availability in order to attract the funding for a full restoration .

[edit] External links

• The International Twelve Metre Association (ITMA)
• Good site for details of all 12 metre yachts built worldwide
• Sparkman & Stephens: The Twelves (Technical explanation)
• Additional information regarding the 12 meter yacht class and the builders behind them
• 12-metre history