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 1901],
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.