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April, 1913 principal features of the design are shown on the drawings. The cargo is carried in two holds, the machinery is placed aft, and water-ballast is car- ried in deep tanks amidships and at both ends. In order to obtain. the maximum carrying capacity the ship is of the awning-deck type, the weight steel being thereby reduced to a minimum consistent with classification requirements. When oil is carried in cases, certain precautionary arrangements are some- times adopted, designed to minimize: danger to the vessel and her crew. In the case of the ship illustrated, for ex- ample, it will be seen (Fig. 2) that the hatchways in the awning deck are of small size, and have steel covers fitted gas-tight. A separate pump enclosed in a gas-tight pump-room is provided to deal with the bilges in the holds. As the vessel is intended to carry ben- zine, the cofferdams shown at each end of the cargo space are a desir- able safeguard, and experience has demonstrated the danger of omitting them when this cargo is carried. No accommodation is fitted directly on the awning deck, the crew are berthed forward, and the officers' quarters, etc., amidships are separated from the oil-deck by store-rooms. A very ef- ficient system of ventilation is fitted, - each hold being provided with four ventilator-pipes, 3 in. in diameter, ex- tending to within 6 in. of the bottom of the vessel and having a_ steam- ejector at the top. Carriage in Bulk As is well known, however, pe- troleum and other oils' are now almost entirely transported over-sea in tank-steamers of special design and construction. In such ships also the cargo is carried amidships; the- machinery is fitted aft, and completely protected by a poop. In a typical ship, 370: 4t.. by. 50: ft. 9m. by -29. ft. 114 in. to the upper deck, the oil is carried in a series of eight tanks, the longest of which are 27 ft. 1 in. in length. A pump-room is_ situated amidships, extending across the full width of the ship. The tanks are divided in the center by an oil-tight division which extends throughout the length of the oil-spaces, pump-room, and cofferdams. An expansion-trunk, equal in width, in this case, to one-half the width of the vessel, extends throughout the oil space from the after end of the forward cofferdam to the machinery casing to which the plating is scarphed. The 'tween deck spaces outside the expansion trunk are utilized as summer tanks. Cofferdams, or safety spaces, are fitted forward and aft, entirely isolating the oil 'point. THE MARINE REVIEW q (> | y YUM bf ht MOGUL. TY ' SS SS Jppemeined 3314.8. FIG, 3--ARRANGEMENT WITH EXPAN- SION TRUNK AT SIDE OF VESSEL spaces from the forward cargo hold and machinery space respectively. In reality the hold immediately abaft the fore peak, although described as a cargo hold, is rarely or never used for that purpose, and usually accom- modates stores. Water-ballast is car- ried in the peaks and in the double- bottom spaces under the engines and boilers. An increasingly large number of oil-steamers are now adapted to burn oil fuel, and storage space for this is provided here in bunkers extending to the poop-deck. This storage space is in some instances supplemented by a long tank constructed in the bottom of the forward hold. | In a discussion of the arrangements briefly noted above the question arises, What is the correct or advisable posi- tion for the machinery--amidships or at the after end? In the early days of tank-steamer construction this was a question often debated, and practice was about equally divided upon the Time, however, in this, as in more weighty matters, has brought about a general agreement on the merits of the question, and, with one or two exceptions, machinery is placed aft in the oil-ships now being built. Position of the Machinery Whatever may be the advantages of - this position from the shipowners' . point of view, it can be said to be a desirable arrangement from the stand- point of structural efficiency. It per- mits the strong construction character- istic of the oil-tanks to be extended uninterruptedly throughout the midship part of the ship. With the machinery amidships, the middle line bulkhead and sides of the expansion trunk 'are terminated at each end of the machin- ery space, and arrangements must be made for tapering off this discontin- 127 uity, which is always a matter of some difficulty. This difficulty is increased by the fact that the long bridge, which is usually fitted when machinery is placed amidships, itself stops in nearly the same place. When the machinery is placed aft the structural arrange- ment is uniform and amidships, and it is not necessary, therefore, as in the former case, to take any steps to ob- viate the decided discontinuity that ex- ists there. It may therefore be con- cluded that an arrangement which con- notes a 'substantial gain in carrying capacity and a reduction of first cost to the shipowner, and at the same time is not inferior structurally, is one the adoption of which is entirely justi- fled. Length of Tank Another point which emerges prom- inently from a discussion of the gen- eral arrangement of an oil-steamer is the length of the tanks in which the oils is to be carried. The saving ef- fected by having one or two trans- verse bulk-heads less in an oil-ship is a consideration that sometimes pre- sents itself with more force to the mind of the ship-builder than does the necessity for keeping the size of the tanks within reasonable limits. Such a necessity exists, however, and experi- ence with oil vessels built before 1909 conclusively proves that the adoption of long tanks, involving, as it does, an. increased mass of oil in each, results in heavy weather damage, sometimes of a widespread nature. A study of the "morbid anatomy" of oil ships: will "reveal" this®=<-The -author fas 'analyzed all cases of recorded sea damage in oil ships during the past thirteen years, more especially in rela- tion to the structural arrangements of © the vessels and the lengths of the tanks in each. The damage consists principally of started and sheared riv- ets, started caulking, and, to a lesser extent, of material deformed and frac- tured. In ships with long tanks, how- -ever--and by long tanks I mean those over 30 ft. in length--this latter ele- ment is more pronounced than in those having tanks of shorter lengths, and in many instances plates and angles in the longitudinal and trans- verse bulkheads have been deformed and fractured, revealing unmistakably the capacity for damage inherent in such large masses of oil when the ship is in a sea-way. Taking all these damage cases in the aggregate, it is found that for them the average length of tank is over 30:ft. Cases of re- curring damage are especially interest- ing, for in them the casual element can be neglected, and in these cases, excluding two small ships more than twenty-five years old, the average eee ie