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38 Bracketless System (Continued from Page 16) for vessels carrying petroleum in bulk. Stated briefly, the Isherwood sys- tem comprises a series of widely- spaced deep transverse frames and beams extending in the form of belts completely round the vessel. The transverse frames, which are riveted to the hull and decks, are slotted round their outer edges to admit the pas- sage of continuous longitudinal stiffen- ers, which are also riveted to the hull and decks. In the case of an oil tanker on the Isherwood system, the longitudinals at the sides, bot- tom and deck of the vessel, as well as MARINE REVIEW head brackets shown in Fig. 1 have caused a fair amount of _ trouble through leakage, and after consider- able investigation, Sir Joseph W. Ish- erwood, Bart., has introduced an im- provement to his system of framing which has for its primary object the elimination of bulkhead brackets, so obviating the danger of leakage at these points, while at the same time maintaining the continuity of longi- tudinal strength. This system is known as the “bracketless-system.” The bracketless-system, as applied to a tanker, is the conventional Isherwood system, but without any brackets what- ever to the longitudinals in the oil tanks. In discarding the brackets the strength of the structure is main- ih March, 1926 two primary functions to perform— first, each to connect its longitudinal to the bulkhead; and _ second, the brackets maintain the continuity of the longitudinals and bind the struc- ture along with the shell and deck plating into a homogeneous whole, the bulkheads forming points of compara- tive rigidity. The bulkheads and deep transverses in combination with the shell and deck plating carry the whole volume of the load, and the longitud- inals serve to transmit their individ- ual small loads to the transverses and bulkheads. Treating the longitudinal members as beams, the stress on each is at a ————————— A TIE ELE LE LD LES AID, SRE 54 || exces Te RE ROTO Rees eee A FIG. 2—BRACKETLESS SYSTEM—STIFFENING SIDE OF BULKHEAD the longitudinal stiffeners on the cen- ter line bulkhead, are all stopped at the transverse bulkheads and_ brack- eted thereto through the medium of the stiffeners on the transverse bulk- heads. The system, with its more scientific distribution of stresses, dis- pensing as it does with the large bulk- head brackets of the old transverse system, greatly minimized the leakage at the bulkheads. This result, how- ever, was achieved only at some ex- pense, which, on the other hand, was more than counterbalanced by the economies effected in other directions. Oil is a particularly searching liquid, and if there is any faulty workman- ship put into riveting, caulking and plate work, then oil will find that weakness very quickly. It has been found by experience that brackets tained by an ingenious distribution of scantlings and material. Fig. 1 is a perspective drawing of the established tanker, and shows at the left, the caulking side and at the right the stiffening side of the bulk- head. Fig. 2 is a similar drawing of the “bracketless” tanker, showing the stiffening side of the bulkhead; and Fig. 3 shows the caulking side of the bulkhead. In Fig. 1 will be observed the large number of brackets connecting the longitudinal members sides and bottom to the bulkheads, and also the brackets connecting the horizontal stiffeners of the middle line bulkhead to the transverse bulkheads. Figs. 2 and 3 show that all of the brackets have been eliminated. It will be appreciated that the bulk- of the deck, - maximum at the points of fixity (or fixity for all practicable purposes), and that is at the deep transverse frames and at the bulkheads. While under static conditions the stress on the longitudinals at the transverses and bulkheads might be the same, yet when the vessel is in a seaway it will be readily appreciated that the maxi- mum work of these members is per- formed at their connections to the bulkheads—the points of maximum rigidity—hence the trouble with bulk- head brackets. The claim of the bracketless-system is that it removes this maximum point of stress on the longitudinal member away from the bulkhead. This has been done by fit- ting the deep transverse frames in closer comparative proximity to the bulkheads than hitherto, that is, in-