America's Cup Racing Yachts
Evolution of a Design - The Early Years
The early America's Cup races from 1870 through 1876 were sailed primarily in schooners. After
that  the cutter took over the scene from 1881 to 1887. For the years 1885, 1886, and 1887
respectively, Edward Burgess of Boston  designed
Puritan, Mayflower, and Volunteer, all
successful cup defenders. In 1893 a new era for the America's Cup and sailboat design began with
the era of the '90 footers' (LWL). These were the largest and most impressive of all the America's
Cup yachts. The 1893 defending sloop
Vigilant was 125-foot LOA and the first of five successful
Cup defenders designed by Nathaniel G. Herreshoff considered by many to be the father of
modern sailboat design. (His next four defenders were
Defender [1895], Columbia [1899 and
Reliance [1903], and Resolute [1920].) The era of the '90 footers' lasted until 1903 climaxing
with the race between
Reliance and Shamrock III.

The existing rule during this era rated only two of the three major speed-related parameters of a
sailboat, length and sail area. As either the length or the sail area increased, the rating increased.
Little else was considered. Displacement wasn't rated at all.  With no rule to regulate it,
displacement became very light, and construction often became somewhat flimsy to keep the boat
reasonably stiff despite the lack of weight. The yachts became too expensive, complicated and
potentially dangerous. Only one major constraint was imposed, the load waterline length of the
boat could not exceed 90 feet. The result was an evolution that produced an extreme scow-type
yacht. Length was measured only at the waterline, so the rule produced a boat with very long
overhangs. On
Reliance these reached  22 ft forward and 26 ft aft. These long overhanging ends
gave extra length on the water when heeled. Sailing close hauled, in seven or eight knots of breeze,
the effective waterline length of
Reliance would stretch out from 90 ft to nearly 130 ft, allowing the
boat to achieve much greater speed. The fin shaped keel came down very deep. The boat would
easily settle into a comfortable heel very easily taking advantage of  16,159 sq ft of canvas on a
single mast, approximately 2000 sq ft more than the challenger
Shamrock III.
Sail plans of a 90-footer racing sloop
Nathaniel G. Herreshoff's Reliance 1903
Nathaniel G. Herreshoff's Vigilent 1893
The next era was that of the Universal Rule and J-class from 1920 through 1937. The Universal
Rule had length and square-root of sail area in the numerator (speed-giving elements) while
cube-root of displacement in the denominator (a retarding quantity). The rule under which the J's
were built was a modified Universal Rule with a set rating of 76 feet. The Universal Rule was
based on ideas proposed by Nat Herreshoff allowing waterline length to be increased without sail
area being restricted, as it had been under the older International Rule. This was compensated by
a larger displacement and so draught was limited to 15 feet.  The rules for the J-class stipulated
that length overall had to exceed about 120ft; LWL had to be between 79 and 87 feet, and they
could displace up to about 160 tons. 1937 saw the building of the last two J's on both sides of the
Atlantic. Both
Ranger and Endeavour II took the waterline length to its extreme, measuring 87
feet LWL.
Ranger, the American boat, was designed jointly by W. Starling Burgess and Olin
Stephens. It was a design combination which produced the greatest J of the fleet, the 'super J' as
she was later known.