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Show U. S.-British Methods Vary In Computing Ship Tonnage To understand news of shipbuilding or of ship losses in the war, the difference between gross and deadweight tonnage must be clearly understood, under-stood, according to the national council of American shipbuilders. If you say a yardstick is 36 inches long, and your neighbor says it is several inches shorter, you won't come out with the same answer when you both try to measure the number of yards in a room with your respective respec-tive yardsticks, the association explains. ex-plains. Those who calculate the tonnage of a ship in the two most widely used measures the gross tonnage used by the British and the deadweight dead-weight tonnage used in this country don't get the same answer, either. Using the British yardstick, a Liberty Lib-erty ship is rated at 7,100 gross tons. American measurement will rate at about 10,800 deadweight tons. All of which makes for confusion, to say the least. To understand what ship tonnages mean, you must first learn that neither nei-ther gross nor deadweight tons refers re-fers to the actual weight of a ship. They are attempts to measure its capacity to carry cargo. A ship's weight is far less important to her owner than the amount of revenue-producing revenue-producing cargo she will carry. In arriving at the deadweight of a ship you measure the volume of , S water it displaces, fully loaded with its crews and supplies, and subtract from that figure the combined weight of the ship's hull, machinery and all of its equipment. That gives the weight of the cargo in the ship, plus crew and supplies the deadweight tonnage, which is expressed in tons of 2,240 pounds. " Gross tons are really not tons at all. That is they are not measures of weight or mass, but of cubic content con-tent like a bushel of corn. It is easy to measure the cubic content of the hull and all enclosed deck structures of a ship. It is not so easy, however, to express cubic content in terms of the weight of cargo a ship will carry. A ship loaded full of hay weighs substantially less than the same ship filled with pig iron. Therefore, in estimating gross tons it is necessary to have some constant factor representing rep-resenting the weight and bulk of an average cargo that will be carried. More than nine decades ago, all maritime countries agreed that in translating the cubic content of a ship into tons of cargo capacity, they would figure that one ton of cargo would fill up 100 cubic feet in the ship. So by dividing the number of cubic feet by 100, they determine its capacity in gross tons. In reading news of shipbuilding programs or of shipping losses in the war, the difference between gross and deadweight tons must always be kept in mind. Remember that Lloyds of London invariably uses the gross ton measuring stick, while Americans prefer deadweight tons as a more exact yardstick of cargo capacity. |