Page 1 - Building A Big Ship

";]:'T'"",;,r, rno c""o,'ry.urnid has a vcrticol ilt1)TH'r'"il ,'"" ."*r,' ur zg0 rcot. " Building a Big Ship \ tr /HEN we want to convey an idea of the size of a vessel we fre- VV quently say she is of ,o many tons," as, for instance, the " great lineirs the Aquitania and the Olgmytic, the tonnage of which is over 50,000, as against the 30,000 odd of the Mauretania. It may be as well to see rvhat this term really means, for verv ferv people knov.. If you put your model sailing yacht into a small bath already quite full of water, what happens ? The boat, to make room for itself, " dis- places I' some of the water, and this flows over the side. Exactly the same principle applies to a big ship ; the vessel and its contents wcigh exactly as much as the volume of rvater,displaced as it floats; this is known as its " displacement tonnage." All warships are calculated on this basis, but in dealing with modern steamships a number of other considerations have to be allowed for. It would take too long to ex- plain in detail how the calculations are made, but they give what are known as the " gross tonnage " and the " net tonnage " of q ship. A gross ton is a hundred cubic feet of all those parts of a ship/rvhich are pe manently closed in. The net tonnage, generally speaking, is the space left after allowance has been made for engine-rooms, boiler- rooms, compartments for stores, and accommodation for passengers, \Y.B.S t37