The 1934 Measurement Rule

The Cruising Club of America's formula for able ocean racing craft

This set of American measurement rules was finalized in 1933 for adoption in 1934 to establish linear ratings for the handicapping or "corrected times" for yacht racing in mixed fleets for the 1934 season. Perhaps, most notably, it introduced "normal and desirable" qualities that, without banning extremes, penalized divergences – point "B" rapidly became known as the "narrow beam penalty" that was not appreciated by a number of owners of British designs, and a few fairly recent American designs including Olin Stephen's Dorade. We have used "The Yachtsman's Yearbook 1934" edited by Alfred. F. Loomis as a reliable source.

THE special committee appointed by the Cruising Club of America to formulate a rule for the Bermuda and other ocean races recommended to the Board of Governors of that organization the following formula, which was approved by the Board and adopted.

In arriving at a rule, the objective was to get one that would prove equitable to the great fleet of existing boats, and, as far as possible, prevent new boats built especially to the rule from having an undue advantage. ‘To this end the committee had the help and the judgment of several naval architects, including Clinton H. Crane, John Alden, Olin Stephens, Philip Rhodes, B. K. Sharpe, and Gordon Munro.

In theory, the rule is based on what is considered the normal and desirable type of fast cruiser, and the various characteristics common to such yachts, such as the generally accepted beam ratio, displacement, draft, freeboard, etc., have been given their normal values. Any deviations from these values are not prohibited, but are taxed, if they are less than the normal, or are given a premium if in excess of normal. Thus, a yacht that complied exactly with the normal values would have zero values for beam, displacement, draft, freeboard, etc., while if her beam, displacement or freeboard were less than the norm, each would be taxed in the formula, and any deficiency in draft would receive a premium. Bow and stern overhangs have been brought under some control in the method of measuring, to prevent undesirable features. Here is the rule:

Rating = .6 √SA x Rig Allowance  + .4L  ± B  ± D  + P  + F  + A  + C

In this formula

SA = Sail Area — To be measured as by the N.A.Y.R.U. with the following changes:

In yachts of all ratings, if the spinnaker pole is longer than the base of the fore triangle, such excess shall be added to such base in computing the sail area of the fore triangle.

Area of the mizzen sail of a yawl, as measured, to be not less than 10% of the total sail area, as measured. That of a ketch to be not less than 18%.

In the event that the area of the mizzen is less than the percentages above mentioned, an additional amount of sail area shall be added in the formula so as to bring the area up to those percentages.

Mast Height Limits: To the highest point of measurement, as follows:

Sloops and cutters: 1.7 √SA + 5 ft.
Ketches and yawls: 1.7 √SA - Mizzen SA + 5 ft.
Schooners: 1.7 √SA - .85 Fore Triangle + 5 ft.

Any excess of height above these limits to be multiplied by 3 and added to the perpendicular P in computing the sail area. Any deficiency below these limits to be divided by 2 and subtracted from the perpendicular P in computing the sail area of jib-headed mainsails. [The "perpendicular P" is measured from the highest point where a halliard is "chock-a-block" to the deck for loose-footed sails and to the tack point for boomed sails.]

Rig Allowances:

Jib-headed sloops and cutters: 1.00
Gaff-headed sloops and cutters, jib-headed yawls and jib-headed staysail schooners: 0.97
Gaff-headed yawls and schooners with jib-headed main and gaff foresail: 0.95
Jib-headed ketches and gaff-headed schooners: 0.93
Gaff-headed Ketches: 0.90

L — The length of a W.L plane, 4% of the L.W.L. above the L.W.L., corrected for jogs, notches or hollows in the profile, and for a transom stern or its equivalent, as follows:

The points of intersection of this plane and the profile must extend beyond the L.W.L. endings.

Any local concave jog or notch (curved or angular) at the plane of measurement at either end shall be bridged by a straight line and LZ taken to the intersections of such lines with the established 4% W.L. plane:
Except that a concave bow profile, producing what is commonly known as a clipper bow, shall be permitted without bridging, provided that all the lines of such bow clearly indicate that it is a true clipper bow and not hollowed in profile for the purpose of unfairly reducing the L measurement.

B — If the maximum beam on the 4% W.L. plane be less than .23 L + 2 ft., the difference is to be multiplied by 2 and inserted in the formula as a plus quantity. If such beam be more than .23 L + 2 ft., the difference is to be divided by 2 and inserted in the formula as a minus quantity.

D — If the draft be greater than .14 L + 1.5 ft., the difference to be multiplied by 2 and inserted in the formula as a plus quantity. If the draft be less than .14 L + 1.5 ft., the difference, in the case of keel boats, to be divided by 2 and inserted in the formula as a minus quantity, and in the case of centerboard boats, such difference to be divided by 4 and inserted in the formula as a minus quantity.

P — If the displacement in cu. ft. be less than either 1.1 (.2 L.W.L. + 5)³ or (.18 L + 5)³, the difference between the cube root of the actual displacement and the cube root of the displacement arrived at as above (whichever is greater) shall be multiplied by 3 and added in the formula as a plus quantity. ^[1]

F — To be the average of the freeboard at the bow and stern endings of the L.W.L plus one-half the average of the rail height, including the rail cap, at these points. The average of rail heights not to exceed 8 inches for credit. If the freeboard, as measured above, be less than 0.06 L + 1 ft., the difference to be multiplied by 3 and inserted in the formula as a plus quantity.

A — If the horizontal distance between the forward end of L and the forward end of L.W.L. exceed 8% of the L.W.L. length (twice the height of L plane above L.W.L. plane), the excess is to be multiplied by 3 and entered in the formula as a plus quantity.

C — If the horizontal distance between the after end of L.W.L. and after end of L be less than one-half the beam on the 4% W.L., at the after end of the L.W.L., or outside to outside of planking at the after end of 4% plane, such difference to be entered in the formula as a plus quantity.

Scantling tables for boats built under this rule are in process of preparation. Until adopted, it is the intention to restrict entries in races under this rule to yachts having a ratio of ballast to displacement of not more than 46%.

Propeller allowances to be decided separately to suit the conditions of any particular race.

In connection with the application of this rule the Cruising Club should appoint a Special Committee. If from any peculiarity of form, construction or fittings, the committee decides that a yacht is not fairly rated by the rule, the committee shall award such certificate of rating as they may consider equitable.

Notes

[ Back ] Footnote 1: We have corrected an obvious typographical error in the second term for comparative displacement (.18 L + 5)³ which erroneously was written by Mr Loomis as (.18 L + .5²)³.