Summary of yacht measurement rules up to 1933
British
Fourteenth Century
100
Often described as being for warships, but may have been used fiscally for commerce.
1694
94
L = "Tread of keel." B = Breadth inside of ceiling. D = depth of hold from under side of upper deck to planking below keelson.
1720
94
1773
94
Builder’s Old Measurement (B.O.M.). L taken along rabbet of keel, from forward perpendicular to after side of sternpost. B taken from outside of planking, excluding heavy wales.
1854
94
Royal London Yacht Club; Royal Mersey Yacht Club. A variant of the 1773 B.O.M. rule. Was often refered to as the "Thames Rule" – see Volante. Length measured on deck to after side of sternpost, and full breadth deducted.
1874
200
New Thames Yacht Club. D measured from upper side of planksheer to lower side of keel.
1882
1738
Yacht Racing Association (Y.R.A.) "1730 rule" (from the denominator.) The last of the pure "cubic" rules.
1886.
6000
Y.R.A. Length and sail area rule. Length measured on load waterline. While mathematically it is 3-dimensional, therefore cubic, it was somewhat incongruous to introduce canvas dimensions into tonnage.
1896
2
First linear rating rule. Girth rule, using G = Skin girth.
1901
2
The second linear rating rule, which continued the use of G, but introduced 'd' - the difference between skin and chain girths, thus taking hollow bilges and lesser displacement into the formula,
1906
2.5
Introduced F as the mean freeboard as a deduction. This may have been 'informally' introduced into the 1901 rule, with or without a change in the denominator.
1919.
2.5
Refined, and lessened, the penalty for heavier displacement.
1928
2.3
For the larger yachts only, removing considerations of displacement and beam.
1931.
The Universal Rule was adopted for the largest class. See also the 1903 American entry below.
1933
2.37
American
1792 : Similar to B.O.M.
1845 : New York Yacht Club. Displacement, by weighing or from model.
1848 : New York Yacht Club. Custom House tonnage.
1850
95
New York Yacht Club. D "true depth," under side of deck to ceiling.
1856 : New York Yacht Club. Sail area. Various clubs. Length over all or "mean length."
1859 : L x B. Length on waterline, extreme breadth.
1870 : Displacement.
1873 : "Cubic contents".
1882
4000
Seawanhaka Yacht Club. Length measured on waterline.
1883
2
Racing Length. Seawanhaka Corinthian Yacht Club.
1884
3
Racing Length. New York Yacht Club. More emphasis on Length, less on Sail Area.
1890
2
Racing Length. New York Yacht Club (Note: this is the "Seawanhaka Corinthian Yacht Club Rule" 0f 1883, adopted seven years later.)
1901
1.1
Racing Length. Seawanhaka Corinthian Yacht Club. L was an average breadth on waterline plane, with coefficient of midship section.
1903
5 x 3√D
Rating. New York Yacht Club. "Universal rule." D, displacement, constant in divisor later changed to 5.5.
1909
3√D
Note that numerator 0.18 reflects a divisor of 5.55, thus further discouraging lightweight construction.
