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

524 ly termed and known as the Danube rule. Another rule, known as the German rule, is to measure the coal bunkers as well as the machinery space, and to allow the total space thus occupied provided it does not -exceed 30 per cent of the gross tonnage, except in _ tugs. In 1873, an international commission on tonnage met at Constantinople to deal with the subject of the Suez canal dues, and although they adopted the Moorsom system of measurement, they made more stringent regulations as to the measurement of deck erections and allowance for engine space. Double bottoms for water ballast, whether con- structed on the cellular or system, MacIntyre are exempted from measure- DRILLING RIVET HOLES ment in the same manner allowed by the English law. The. Suez canal rules for measure- ment of deck erections will not be discussed here as they. can easily be learned from those rules. The Danube commission accepted, in 1876, the Suez canal rules, so that the same certificate is now available for both. In vessels with fixed coal bunkers, the German rule may be used for ob- taining the allowance for propelling space, while vessels with shifting bunk- ers are measured by the Danube rules, and the maximum allowance for crew spaces, galley spaces, W. C.'s and navi- gation spaces is 5 percent of the gross tonnage. The Moorsom tonnage measurement has been adopted by most of the mari- time nations of the world, although the allowances for engine space differ in some cases, and the crew space deduc- tions for nearly all countries are lim- THE MARINE REVIEW ited to 5 per cent of the gross tonnage. Freight tonnage is simply a measure of cubical capacity, a freight ton being 40 cubic feet of space. This tonnage has no legal authority, but is largely used by merchants and shipowners as a measure of the capacity of vessels. Register tonnage is a measure of a vessel's internal capacity, a register ton being 100 cubic feet. of itternal space. Displacement is a measure of the weight of a vessel and her outfit and cargo, a ton of displacement being 20 hundredweight avoirdupois. The weight ofa floating body is equal to the weight of fluid displaced, and in order, therefore, to ascertain the weight of a vessel and her contents at any given draft, it is only necessary q IN HUGE BOILER HEAD to calculate the weight of the volume of fluid displaced. As the register tonnage is that upon which a vessel has to pay dock and other dues, while the deadweight carry- ing Capacity represents the earning power of an ordinary cargo vessel, it is obvious that from a shipowner's point of view the most profitable ves- sel is the one which can carry the greatest amount of cargo in relation to her register tonnage. The method of estimating the official tonnage known as the "builder's old measurement rule" in which the square of the breadth entered into the calcu- lations while the depth was neglected fostered the. building of dangerously narrow and deep ships with very full forms, so as to produce a large carry- ing power with a comparatively small official tonnage. The present tonnage laws aim at ascertaining accurately the internal Capacity of the vessel, and there is not September, 1920 now the same inducement to build such badly proportioned ships. The displacement of a vessel is calcuy- lated from the drawings, and _ the method of calculation is similar in prin- ciple to that adopted for the measure- ment of the internal capacity; but the naval architect is not fettered by any definite number of subdivisions as laid down in the tonnage laws. The area of each section is calcy- lated by means of Simpson's rules and the areas of these sections then treated as ordinates of a curve of sectional areas, the result being the volume in cubic feet. To this volume must be added the volume of any appendages, such-~ as keel, rudder, etc., so as to obtain the total volume displaced. Thirty-five cubic feet of salt water weigh 1 ton; if, therefore, the volume in cubic feet be divided by 35, the result will be the displacement in tons, It is usual in carrying out this calcu- lation to arrange the ordinates of the various sections and waterlines on a sheet in such a manner that the areas of each may be readily ascertained and at the same time to calculate the center of buoyancy, or the center of gravity of fluid displaced, and to construct curves of displacements and tons per inch immersion. The curve of displacement is con- structed by setting off the displacement -as calculated at different drafts (mean), or ordinates of -a curve on any con- venient scale, so that the displacement at any intermediate mean draft may be ascertained without the labor of separate calculations, by simply measur- ing with the same scale the length of the ordinate at any given draft. The curve of. displacement is usually as shown in Fig. 3, and is, of course, only to be used for obtaining the displace- ment at any mean draft of a vessel on a fairly even keel. The displacement at any exceptional trim would have to be calculated separately. Rolls Big Boiler Head The largest, single-piece boiler head ever made was recently rolled in the Coatesviile, Pa. mills of the Lukens steel Co. for -the. Bath Iron: Workg, Bath, Me. . The illustration shows the drilling of rivet holes for two of these boiler heads. These were flanged at the mills. The circular plates from which they were made were 199% inches in diameter before turning the flange. The material is 48-inch thick and the completed head weighs 8820 pounds. After turning the flange, the outside diameter was 183 inches. The boilers when completed are to be used in vessels now building at the Bath Iron Works. i a a ea ae ie ink Sl