SHIP TERMS

Waipa Post, Volume 49, Issue 3555, 8 December 1934, Page 4

SHIP TERMS

TONNAGE AS IT RELATES TO OCEAN VESSELS. 0 Commander J. G. Bissett, master R.M.S. Ascania, unveils some of the mysteries and explains some lof the technicalities of ship terms for the benefit of the landlubber, in the following article: — Those people about to make a sea voyage, who take the trouble to look up some details about the ship they are to sail in, may be struck by the disparity which exists between the figures indicating the size of the vessel, such as gross tonnage, register tonnage, displacement, and dead weight. For instance, the figures for the famous steamer Mauretania are as follows: Gross 30,696 tons Register 12,797 tons.. Displacement (loaded) 44,640 tons Let us briefly examine each of these terms and see what relation they bear one to another. Firstly, it should be clearly understood that the word 'ton' used in this respect does not mean a ton weight in the sense in which a landsman uses the term. It is, in fact, a tonnage unit, or ton measurement, and represents a space containing 100 cubic feet. GROSS TONNAGE. This expresses the total capacity of the ship in tonnage units, and consists of the sum of the following items: (1) Under deck tonnage: The cubical capacity of the space below the "tonnage'' deck, which in ships having less than three decks, is always the upper deck, and in all other merchant ships, the second continuous fort and aft deck from below. (2) Between deck tonnage: The cubical capacity of spaces between the tonnage deck and decks above it. (3) The cubical capacity of all permanently closed spaces on the upper deck, such as passenger and crew accommodation, storerooms, deck houses etc. REGISTER TONNAGE. This figure is supposed to represent the comparative freight earning capabilities of the vessel, and most of the charges borne by ships, such as dock and harbour dues, light dues, pilotage fees, etc., are levied upon it, therefore it is a figure of great importance to the shipowner from an economical point of view. It is obtained by making certain deductions from the gross tonnage, the principal ones being—propelling space, including engine and boiler rooms, the shaft tunnel, and any spaces above the upper deck used for auxiliary machinery. ACCOMMODATION. This includes living accommodation for all members of the crew, but not passenger quarters. Also storerooms, sail rooms, chart rooms, wheel houses and all such spaces used exclusively for the navigation of the vessel. All the above spaces must have the purpose for which they are allotted marked on a beam overhead such as "Certified to accommodate one seaman.'' "Certified as paint store.'' "Certified to accommodate the Master," etc. The following report of the International Tonnage Commission, held at Constantinople in 1873, may be quoted with interest: "It has been the traditional of all maritime countries to submit merchant vessels to a measurement, the result whereof, known under the general term of "Tonnage," serves as the basis of taxation to which a ship is, or can be made, liable everywhere and under any circumstances." The fixing of the tonnage is the duty of the governing authority of the country to which the ship belongs, and is of course compiled under strict, international rules. The official document upon AVhich the tonnage of a British ship is noted, is known as the "Certificate of Registry," and is issued after survey by the Board of Trade. DISPLACEMENT The first law of hydrostatics status that a body floating in a fluul displaces a volume of that fluid equal in weight to the floating body, therefore the displacement of a ship is its actual weight at any time. It may be expressed in cubic feet of water displaced, which is known as "volume of displacement," or this figure divided by 35 will give displacement in tons weight. (Sea water is 35 cubic feet to the ton.)

From the foregoing it will be readily understood that displacement varies with the condition of the ship, that is, whether she is light or loaded, or in other words, whether she has on board cargo, fuel, water ballast, or any other weight than her structure.

It would not be fitting to close this article on tonnage without mention of Samuel Plimsoll, whose unremittingefforts to render more secure the lives of sailormen, entitled him to a place of honour among those who do business upon the great waters, j Due to his forceful presentations ot the conditions then existing in the Mercantile Marine, a Royal Commission in 1875 decreed it necessary for every British ship, and every foreign ship trading to a British possession, to have painted on her sides a load-line mark beyond which she must not be loaded.

This mark, known as the Plimsoll Mark, will be found on each side of every vessel, about the middle of her length, and in the vicinity of her load-

ed water line. Its position is determined by experts after careful and abstruse calculations relative to the reserve buoyancy of the vessel. Most people who inspect ships when in port have noticed, or looked for, the Plimsoll .Mark. The modern Plimsoll Mark as required by the Merchant Shipping (Safety and Load Line ventions) Act ,1932, is indicated by a circle, with a parallel line through the centre, the ends of the line being marked L. and R. These letters stand for Lloyd's Register, under whose supervision the ship was measured. The line immediately above the disc is the main deck line. ■ The distance between this line and the centre of the disc is known as freeboard. "T.F." is the line to which a ship may be ldaded in the tropics in fresh water. "F'' (a little lower down on the hull) is the. height above the centre of the disc which may be added to any of the markings when the ship loads in fresh water! "T" is the load line in salt water for the tropics. "S" is the summer load line, and "W" is the winter load line. "WNA" is the load line for the winter in the North Atlantic. The boundaries of the zones and seasonal areas are distinctly laid down in the articles of the Convention. The disc is twelve inches in diameter (outside) and the horizontal discs one inch in thickness, the upper edges being always used in computation. Supposing a ship to be loading in salt water at a port where she is allowed to load to the line "T," and the scale shows the draught for this line to be 28ft, she may, if desired, load to 27ft forward and 29ft aft. This may be done intentionally to improve her steering qualities, or it may be unavoidable owing to the distribution of the cargo, but the figures mean a mean draught of 28ft, which is what the law demands.