Appendix IV
RULES FOR TONNAGE MEASUREMENTS
THE English system of measuring the tonnage of vessels in the eighteenth century is given in Falconer’s Marine Dictionary, 1780, as follows:
“To determine the burden, or, in other words, the tonage, of a ship, it is usual to multiply the length of keel into the extreme breadth of the ship within board, taken along the midship beam, and multiplying the product by the depth in the hold from the plank joining to the keelson upwards to the main-deck, and divide the last product by 94; then will the quotient be the burden required, in tons.�
This rule continued in force till 1819, when it was changed by the Lords Commissioners of the Admiralty as follows:
“Multiply the length of the keel by the breadth of beam, and that product by half the breadth of beam, and divide the last product by 94, and the quotient will be the tonnage� (Marine Dictionary, William Burney, LL.D., 1830). Dr. Burney remarks: “It appears from the general construction of merchant ships, that more attention is paid to evade the tax on tonnage than to their sailing well with the wind in different directions; and if the real tonnage of ships were taken, an alteration would soon be made in the construction for the better.�
This form of the rule continued until 1842, when by Act of Parliament the following method was adopted:
“Divide the length of the upper deck between the after part of the stem and the fore part of the stern-post into six equal parts. Depths: at the foremost, the middle, and the aftermost of these points of division, measure in feet and decimal parts of a foot the depths from the under side of the upper deck to the ceiling at the limber strake. In the case of a break in the upper deck, the depths are to be measured from a line stretched in a continuation of the deck. Breadths: Divide each of those three depths into five equal parts, and measure the inside breadths at the following points—viz., at one fifth and at four fifths from the upper deck of the foremost and aftermost depths, and at two fifths and four fifths from the upper deck of the midship depth. Length: At half the midship depth, measure the length of the vessel from the after part of the stem to the fore part of the stem-post; then, to twice the midship depth add the foremost and the aftermost depths; add together the upper and lower breadths at the foremost division, three times the upper breadth, and the lower breadth, at the midship division and the upper and twice the lower breadth at the after division, for the sum of the breadths; then multiply the sum of the depths by the sum of the breadths, and this product by the length, and divide the final product by three thousand five hundred, which will give the number of tons for registerâ€� (Young’s Marine Dictionary, 1846).
In 1854 this rule was changed by the Merchant Shipping Act, which provided that the actual cubic contents of a vessel’s hull should be measured, a registered ton being reckoned as 100 cubic feet. This is known as the Moorsom system, and is still in use and likely to continue. It was adopted by the United States in 1865; Denmark, 1867; Austria, 1871; Germany, France, and Italy, 1873; Spain, 1874; and Sweden, 1875.