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Sail - The 12 Meter
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The "12-Meter Designs" collectively refers to a series of racing yachts designed to compete for the America's Cup.

What are the 12-Meter Designs?

In order to ensure that racing tested the skill of the sailors more than the boat technology, criteria were dictated which competing boats had to meet in order to be qualified to race. From 1958 to 1987, the "12-Meter" Rule was used to ensure that similar designs competed for the America's Cup, while still encouraging yacht designers to balance several key design factors in order to produce the fastest boats possible.

Simply put, the 12M Rule is as follows:


L= The length in linear units, measured at a height of 1.5% of the class rating, (12 meters or 39.37 feet), above the flotation line, adjusted for the girth measurements forard and aft.

d= The difference in linear units between the skin girth and the chain girth, measured vertically in the transverse section at 55% of LWL, from the covering board to a point 12.5% of the class rating below the waterline.

F= freeboard in linear units between the skin girth and the chain girth, measured vertically in the transverse section at 55% of LWL, from the covering board to a point 12.5% o fthe class rating below the waterline.

S= Sail area in square units, controlled by spar dimensions and consisting of the sum o fthe mainsail area plus 85% of the fore triangle.

2.37 is the mathematical constant.

When all measurements are taken and divided by the constant, the result should be close to 12 meters. This does not mean that racers classed as "12-Meter" boats were 12 meters long! In fact, the 12-Meter racers ranged between 65 and 75 feet in overall length. Masts were typically about 85' high, and the boats themselves displaced approximately 25 tons.

In practice, the Rule was much more complex and open to interpretation. The 12M rule book contained more than 20 pages of finely printed text. Yacht designers attempted to take advantage of every loophole and omission to create the fastest design possible while still complying with the Rule. By increasing or decreasing the length of the hull, sail area and freeboard, the designer attempts to balance these effects with the shape of hull, keel and rudder while trying to create the least amount of resistance, the greatest amounts of stability and lift.

Sparkman & Stephens and the America's Cup

Since 1930, S&S has been heavily involved with the America's Cup, designing many of the most famous and successful Cup defenders. Prior to 1958 and the 12M Rule, the last America's Cup was raced in 1937 under the International Rule. This rule produced a class of racers called the J-Boats. In 1937, the J-Boat Ranger, designed by Olin Stephens, in collaboration with W. Starling Burgess, was victorious, marking the start of a tradition of winning designs that ensured American dominance in America's Cup 12-Meter racing for the next four decades.

Design 279 - Vim

VimVim was a stepping off point for Sparkman & Stephens and our involvement with 12-Meter design. Following the 1934 and 1937 victories by Ranger, which had successfully campaigned for the America's Cup with Olin Stephens as helmsman, it was only natural for the firm to turn to the task of twelve meter design.

Vim Sail Plan Designed and built for Harold S. Vanderbilt in 1938, Vim was built to be an all-out racehorse. The sole purpose was to win races, and nothing was included in her design which did not contribute toward that goal. S&S took advantage of major developments utilizing smaller scale (3-foot versus the normal 20-foot) models at the Davidson Institute towing tank to perform extensive performance modeling. At the same time, Vim was the first twelve to have rod rigging and an aluminum spar package. She was shipped to England for the 1939 season and proceeded to easily beat such famous contemporaries as Tomahawk and Evaine, sending a clear message to the Royal Yacht Squadron that American designers had leaped ahead in design technology.

Vim was to remain the standard by which other twelves would be measured for the next twenty years, as she sat in storage through World War II, awaiting the changes to the International Rule that would bring about the 12-Meter revolution of the America's Cup in 1958.

The Champions - A Chronology of S&S 12-Meter Winning Designs For the America's Cup

Year Boat Syndicate
Henry Sear Syndicate
W. S. Gubelman & E. Ritter Syndicate
W. J. Strawbridge Syndicate
W. J. Strawbridge Syndicate
R. McCullough Syndicate
King's Point Fund Syndicate
Fort Schuyler Foundation, Inc.

Designs 1343 and 1773
Columbia and Constellation

1958 saw the first America's Cup challenge using the new twelves. All summer long in preparation for the challenge, Vim and the newly-launched Columbia faced off to select a defender. After weeks of evenly-matched racing, it was only in the final trials that Columbia was able to pull ahead, and it was widely reported that the victory was made possible only by the superior physical endurance of her crew. Columbia Sail Plan

Although Olin Stephens has called Columbia simply "an improved Vim," this reverse-transom twelve meter represented another step toward a more modern racing look. However, it was the subsequent Constellation of 1964 which incorporated more obvious design innovations.

Constellation Sail Plan

During this period, Olin experimented with how the wetted surface of a hull could be reduced (for less drag and greater speed) without endangering the seaworthy qualities of the boat. As a result of his model testing, he concluded that "wetted surface aft was not as harmful, perhaps, as it was forward because the water by then was already going with the boat," leading to the creation of a "bustle" in the waterline of Constellation. Constellation's keel was also modified as a result of his experiments; the keel is short and vee-shaped at the bottom - an innovation that improved windward performance by reducing leeway.

Designs 1834 and 2085
Intrepid and Courageous

At the same time as Columbia and Constellation were making headlines, the S&S team was already at work striving to produce even more advanced twelves for the defense of the cup. The result of this effort was Intrepid in 1967, and Courageous in 1974. Both were dazzlingly successful.

Olin Stephens regards Intrepid as his "most innovative twelve," with a distinctive knuckle bow to cut down weight, and a trim tab. Although such tabs had been introduced on smaller racing hulls, this was the first twelve to risk the innovation. On Intrepid, the steering system was really a matter of two rudders in tandem, a deep one on the keel and a shallow one on the skeg. Intrepid Sail Plan

The former, the trim tab, was used to drive the boat to windward, and to help her turn quickly in tacking duels. The skeg rudder was for steering. Three concentric wheels on the pedestal controlled both. The outer one turned the rudder, the middle one turned the tab, and the small one locked both rudders so they could turn together.

Intrepid featured a very low boom, made possible by locating all of the winches below deck. This design followed the theory that if a main boom were located right down at deck level, the "induced drag" of the sail would be reduced and the sail's effectiveness greatly improved. This theory proved correct. This same effect had been used successfully on the head sails of the earlier twelves such as Constellation in 1964, where Rod Stephens noted that "the foot of the genoa was so close to the deck that it was hardly possible to get a hand under it."

Courageous Sail PlanWith such radical improvements, Intrepid completely dominated 12-meter racing, until the arrival of Courageous. A revision of America's Cup regulations allowed for Courageous to be constructed from aluminum, making her both lighter and faster . After a successful Cup defense in 1974, she was challenged by a number of new U.S. rival designs in 1977. Benefiting from constant fine-tuning, she succeeded in defeating them all. Then, with Ted Turner at the helm, she went on to wallop Australia. Not until 1980 was she defeated by a youngster-the S&S 12-meter Freedom.

Design 2368

Freedom Sail Plan Freedom was the last of the S&S twelves, successfully defending the America's Cup in 1980. The design was a winner - but the race is remembered for more than the victory.

On the first of the five races of that contest, sailed in a shifting, 10 knot easterly, Freedom suffered the indignity of having her rudder linkage break on the second windward leg. On the next downwind leg, lack of rudder control proved no large problem, as the skipper (Dennis Conner) could steer with the trim tab. But for the final upwind leg, it was necessary to try wrapping a line around the rudder post and leading this to a genoa winch. Steering by this winch device and the trim tab proved manageable but clumsy:

Freedom was forced to feather upwind and to make a major operation of each tack. Nevertheless, her crew performed these maneuvers with such skill that Conner, after winning the race, saw no need to mention the breakage. Instead, he dodged questions about why he had sailed the final leg the way he did, admitting only that his tactics had been 'unorthodox.' Thus developed a theory that the canny skipper was really holding Freedom back in an effort to conceal her real speed."

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