The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

¢ Practical Ideas for the Engineer Rules for Calculating Tonnage--How Present Methods Have Been Evolved--Influence of Rules on Ship Design BY LIEUT. COMMANDER CARL H. HERMANCE, U.S. N. R. F. \ HE term tonnage appears to ; have originated from the tun, cask of wine, the earliest sys- tem of measuring vessels being simply to count the number of casks or tuns of wine which could be carried and thus obtaining a measure of the internal capacity. In the reign of Henry V, A. D. 1422, the first act dealing with the measure- ment of vessels of which any record can be found, required "Keels that carry coals at New-castle to be measured and marked," but it is not known how the measurement and markings were at that time carried out. In the year 1679, an act of the British parliament extended the above regulation to the Wear, and prescribed that the Bowle Tub of Newcastle, containing 22% gallons Winchester measure, and "al- lowing 21 bowls of coal to be meas- ured by such Bowle Tub by _ heap measure,' in measuring these river craft. should always be used. The "keels" were marked by nails - upon the bulkheads at each end of the cargo space, or by driving nails into the stem and _ stern-post to _ indicate the corresponding load. draft. In the year 1694, another act of the British parliament was passed for the measurement of keels, and a _ weight was then fixed upon as a standard, in- 'stead of a measure. This act required "keels to be measured by putting into them dead-weights of iron or _ lead, allowing 53 hundredweights to every 'chaldron of coals, and a maximum load of 10 chaldrons or 26% tons." The load-line was then marked on the stem, stern and each side amidships. By an act passed in 1775, the fore- going regulations for the Tyne and Wear were extended to vessels loading coal at all other ports of Great Britain, but the ton of 20 hundredweight avoirdu- pois was then made the standard weight, instead of the chaldron weight. The foregoing remarks relate 'to river craft only, First Rule of Measurement The measurement of ships, as tinct from the rough estimates nage which are found in early records, appears to date from the first part of the seventeenth century, and the earliest Reprinted from the Proceedings of the U. 8. Naval institute. dis- of ton- rule which can be found is that given in Admiral Sir William Monson's tracts, published after his death in 1642. It is termed "A rule to know the burden of a ship: length of keel, 120=Teet; breadth in beam, 40 feet; depths in hold, 20 feet; 40X20X120--96,000 and 96;000--100=the burden, 960 _ tons." From a book entitled The Complete Shipwright, written by Bushnell in the seventeenth century, we learn that the shipwrights of London on the River Thames had a custom of calculating the tonnage of a vessel by the follow- ing rule: "They multiply the length of the keel into the breadth of the ship at the broadest place, taken from out- side to outside, and the product of that by half the breadth. This second prod- uct of the multiplication they divide by 94, or sometimes 100, and according to that division they are paid for so many tuns." Bushnell proposed to ascertain the true measure of a ship's ability to carry, by first marking the water line when ready' for sea without any cargo on board, afterward marking the lead- line, and then measuring the cubic con- tent of the body of the ship between these lines. This appears to he the earliest recorded suggestions of a method of. measuring, displacement between the light- and load-lines, but the manner in which it was proposed to estimate this displacement was a crude one. It will be observed that the rule quoted differed from Monson's by sub- stituting half of the breadth for the depth of the hold. This was a change much for the worse, but probably the half breadth was taken because the depth could not be measured when the vessel was laden, and for the ships built about the time the assumed pro- portion of the breadth to depth was a fairly correct average. The first tonnage rule embodied in the act of the parliament of England was that given in the act of 1694, which levied certain duties upon seagoing and coasting vessels, and is as~ follows: : Ex BxD Tonnage = melee 94 where . length L is length of the keel taken within board (so much as she treads the ground). B is the breadth within board by the midship beam, plank to plank. D is the depth of the hold from plank below keelson to the under part of the upper deck planks. Two years later the tonnage dues on shipping were repealed, and in that year (1696) the first act providing for the registry of shipping appears to have been passed. In 1720, a rule for the measurement of vessels, which was ultimately known as builders' tonnage, was first legalized in an act intended to prevent smuggling, by prohibiting small vessels of "30 tons burden and under from carrying spir- its.' This rule differed from that given in the act of 1694, in that half the breadth was substituted for the depth, thus making the rule the same as that previously referred to as the practice adopted by the Thames shipbuilders. Fostered Poor Ship Designs In 1773, a general rule for the meas- urement of all merchant vessels was made by Act 13 George III, and this, with some slight modifications, con- tinued in force till 1835, and had a most evil effect upon naval architecture. This rule is as follows: (L-- 368 X exe Tonnage B.-O:) M; == ------ ------ 94 where length L is taken on a straight line along the rabbet of the keel from the back of the -main sternpost: to a_ perpendicular line from the fore part of the main stem under the bowsprit. B is the breadth from outside to outside plank in th: broadest place in the ship, be it either above or below the main wales, exclusive of all man- ner of doubling planks that may be brought upon the sides of the ship. The principal difference between this- rule and that given in the act of 1720 is the manner of taking the which the latter act defined as "so much as treads on the ground"; and as this was probably uncertain in prac- tice, the new length for tonnage was obtained by deducting three-fifths the breadth from the length. Thirteen years later, the act of 1773 was supplemented by the law for measuring the length of a vessel when afloat. The length was to be _ taken on the load water line from the back of the stern-post to the front of the main stem, and subtracting from it 3 length, | a a a ad ail aie a al