Note 170 — Chapter IV

Builders’ measurement, or O.M., is the measurement of a vessel according to the old law of 1773 (13 George III., Chap. LXXIV.) which prescribed as follows: “The length shall be taken on a straight line along the rabbet of the keel of the ship, from the back of the main stern-post to a perpendicular line from the fore part of the main-stem under the bowsprit, from which substracting three-fifths of the breadth, the remainder shall be esteemed the just length of the keel to find the tonnage; and the breadth shall be taken from the outside of the outside plank in the broadest place in the ship, be it either above or below the main wales, exclusive of all manner of doubling planks that may be wrought on the sides of the ship; then multiplying the length of the keel by the breadth so taken, and the product by half the breadth and dividing the whole by ninety-four, the quotient shall be deemed the true contents of the tonnage.”

Though another Act was passed in 1834 (Act 5th & 6th William IV. Chap. LVI.) which was again amended by the 6th & 7th Victoria, Chap. LXXXIV., and consolidated by 8th & 9th Victoria, Chap. LXXXIX., known as the “new measurement, or N.M.” the old law remained in use with all shipbuilders in their contracts until 1854, when the law (proposed and carried out by Moorsom) now in force, was passed. By this law, the internal cubic contents of a ship are ascertained, and the register tonnage (on which all fiscal dues are levied) ascertained by certain calculations which produce as nearly as possible the same results in the old measurement of all ships built since 1854 (see ante, vol. iii. note, p. 310), and thus the necessity is avoided of altering the rates charged upon shipping, for light, dock and other dues; under the present law, which is generally approved, an allowance is made for the space occupied by the engines in steam-vessels, so that the register tonnage on which all dues are levied is the gross admeasurement, less the space occupied by the propelling power. The mode of arriving at this, adopted by different nations, has of late been a question of much discussion with reference to the dues charged on vessels passing through the Suez Canal.