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j + i ' t 3 1899.] MARINE: REVIEW. 23 surface occupied for the complete boiler plant must be as large as possible. The units should be large, the grates short and not too wide. The pas- sage of gases through the tubes should be sufficiently long to ensure economy. These gases should be well mixed before entering the spaces between the tubes for the same reason and to prevent smoke. The circu- lation of the water in the boiler must be free. Tubes should not be too long and the fire rooms must always be sufficiently wide to provide for free withdrawal. : The foregoing is what we want. We have most of the above desid- erata in several well-known types of boilers, and ultimately we shall dis- cover the value of each of the foregoing points, and then it will be possible to differentiate between the various types more perfectly than we now can. In the meantime, all that I have to say is that the use of water tube boilers has been definitely decided upon for our naval vessels, because water tube beilers give tactical advantages of great moment, and because, with care in the selection, manufacture, and management of water tube boilers, other disadvantages may be neutralized. SHIPS OF THE GREAT LAKES. MR W. I. BABCOOK, GENERAL MANAGER OF THE CHICAGO SHIP BUILDING CO., DESCRIBES FOR THE SOCIETY OF NAVAL ARCHITECTS AND MARINE ENGINEERS, THE SYSTEM USED IN THE CONSTRUCTION OF . THE HULLS OF LARGE BULK FREIGHT CARRIERS. While the systems used in the construction of the hulls of modern steel vessels are somewhat the same in all lake yards, it is the purpose of the following article to describe the practice of the Chicago Ship Building Co. only, and that as applied to the ordinary lake bulk freight vessel of large size. For a proper understanding of what follows, it is necessary first to describe the ship itself, inasmuch as the requirements of the service have developed a somewhat peculiar type of vessel. The great majority of modern steel lake vessels are designed to carry only iron ore, coal or grain in bulk, and no deck, therefore, is required or laid on the main-deck beams in the cargo holds. The movement of ore and grain is entirely from upper to lower lake ports, and of coal in the opposite direction. As, how- ever, there are a great many wooden vessels still in service which require up-cargoes, and coal cannot be unloaded rapidly, the freight rate on coal is seldom attractive, and the big steamers, especially those belonging to the great ore and steel companies, go back light, using water ballast alone when any is required. The season of navigation being limited by ice to about seven months in the year, despatch in port is of the utmost necessity, and as the cargoes are all spouted in, the ore and coal from elevated docks and the grain from elevators, and taken out by machinery! on the docks, hatches are many in number, and no hoisting machinery is carried on the ships them- selves. The connecting channels 'between the lakes being comparatively shallow, the vessels are built with a plate keel, very flat floor and full model to get as great capacity as possible on the limited draught available, and a large number of frames amidships are exactly alike, as many as one-half to two-thirds the total number. When coming light to a loading dock, they therefore float very high out of the water, and to obtain the necessary slope to the spouts the hatches are made as wide as possible athwartships, leaving only stringer enough for strength on each side. While it is true that the upper deck could be depressed by filling the water bottom, this would cause a loss of time in loading, as it is evident that the cargo can be run in much faster than the water could be pumped out, and is, there- fore, not allowable. The longest straight run in open water is across Lake Superior, some 400 miles, the total voyage being under 1,000 miles. Coal for fuel being available at various points in the connecting rivers, no great bunker capacity is required, and, the fuel hatches opening in all cases through the upper deck, a few minutes suffices to spout in the amount desired from elevated pockets.- At lower lake ports it is usual while the cargo is discharging to fuel from a lighter alongside provided with a hoist- ing derrick reaching into the fuel hatch. ' The danger of grounding in the narrow, tortuous, and in many places rocky channels connecting the lakes themselves being considerable, double bottoms are a necessity and are carried straight across on top to protect th bilge to the upper turn. To get sufficient water ballast, as well as to raise up an ore cargo and make the ship easier in a seaway, the tank is made deep, from 5 to 6 feet at the center line. Carrying the cargo at this height above the floors requires heavily stiffened and closely spaced girders or longitudinals, which are intercostalled between floors to further support them and the bottom plating against grounding strains. The use of chan- nel floors for the flat bottom is now universal, and results in a consider- able saving in first cost, as well as avoiding the continual shearing of frame tivets and cracking of frames through the rivet holes from grounding | when the bottom construction is the ordinary plate floor with frame and reverse bar. Ore and coal loading docks having the spouts uniformly 12 feet centers. all hatches are spaced 24 feet centers fore and aft, and the frame spacing is always 24 inches, no matter how large _the ship, the frames. being channels. Hatches are 8 feet fore and aft and channel, web frames or belts are spaced every 8 feet, making one belt at each hatch bean and one in the center between hatches, on which a main-deck beam is also placed. To avoid interruption of the loading spouts by machinery spaces, as well as to avoid the inconvenience of a shaft alley in the cargo hold, the machinery is placed aft, the engine going as near the stern-post as the shape of the ship will permit, and the boilers and bunkers being next forward, either in the hold or on a raised deck, with cargo space beneath. From all of the above considerations a type of vessel has been devel- oped, of which the steamer Mauna Loa* of the Minnesota Steamship Cox just completed in the Chicago yard, may be considered a fair example. The ship is 430 feet keel, 450 feet over all, 50 feet moulded beam, and 28% feet moulded depth, with a 5%4-foot water bottom. She is propelled by a quad- ..----------_--___-- *Mr. Babe , d by some twenty or more pla'es that fllus- ock's paper is accompanied by {the Minnesota company's steamer trate the system pursued in the construction o &una Loa, Saadtmanious apnea! ions of pneumatic tools are also shown, but thane or similar illustrations have been so often printed in the Marine Review, at there is no need of reproducing them. ruple-expansion, four-crank, jet condensing engine of some 2,500 H. P., taking steam at 250 pounds pressure from two Babcock & Wilcox marine water tube boilers. The light-load displacement is about 3,200 net tons, and on 18 feet 3 inches draught she carried 6,816 gross tons of iron ore. The water ballast capacity is 2,900 net tons. Speed loaded, 12 statute miles per hour, and light, 14 miles. The system used in the Chicago yard in constructing this ship and similar vessels is as follows: The general dimensions, midship section, and positions of hatches and bulkheads having been agreed upon, a model is prepared, and from it the length of the straight midship portion of the ship determined. At the same time, a butt plan of the keel, bottom plating, center keelson, rider, longitudinals, tank margin, and all fore and aft angles is prepared, and on the mould-loft floor a reproduction of the midship section drawing is made full size. From this the widths of the various bottom and bilge plates are measured exactly, the necessary allowances made on the outside plates for bevel shearing and the mill orders prepared at once. Wooden templets for the brackets at center keelson, bilges, tank top, and deck beams are made with the necessary allowance for flanged edges and sent direct to the plate mill, so that all these brackets come into the yard sheared to exact size. The lengths of the channels for floors and tank-top seam straps, and of the angles for the keelson and longitudinal stiffeners, 'bilge frames, etc., are taken directly from the floor and orders sent to mill. It will be understood, of course, that as there are a large number of dead flat frames--114 in this ship--this enables a large quantity of material, both plate and shapes, to: be ordered in duplicate pieces from the floor-very quickly from the mid- ship section only, and without waiting for the body plans to be completed. After the lines are faired and the 'body plans 'completed on the floor, the remainder of the ship is ordered in the usual manner. The laying down in the loft being completed, the next step is the making of the wooden moulds, For the straight part of the vessel amidships, below the tank top, it is evident that one mould only is required for the channel floors, with strip (narrow) moulds for top and bottom flanges, one for the ordinary bilge brackets, and one for the belt bilge brackets, from which all are punched. Also that one mould each suffices for the center vertical keelson and rider for all plates from the forward collision to the*engine bulkheads, the keel- son being of uniform depth, and one keel mould answers for all the keel plates until the floor line at either end leaves the dead-rise line within the half breadth of the keel plate. For this keel mould, as well as for all moulds for butted plates, strips of lignum-vite, adjustable for screws, are fitted into the ends, so that any variation in length from swelling ar shrinking of the pine from which the mould is made can be taken up and the exact length secured. When lapped butts are used this refinement is not required. One mould also answers for nearly all of the center vertical keelson brackets; two moulds for C. V. K. angles, one for each flange; one for the stiffeners of each longitudinal for all the flat of bottom; two for keel bars; two for top C. V. K. angles; two for channel seam straps under tank top; two each for top and bottom longitudinal angles; one for the high plate floors dividing the separate compartments of the water bottom. For the skin plating on the flat of bottom one mould suffices for all the plates in each -strake. Similarly, one mould answers for all the tank-top plates except where the water-tight floors would come at a seam, which is undesirable for water-tightness, and, therefore, avoided by putting in a narrow plate, and one mould for all the tank-top margin plates amidships. ---- In laying out all fore-and-aft members, both plates and angles, from these moulds certain allowances must 'be made, as follows: Where the turning space comes--that is, where the siding flange of frames and floors' changes from looking aft to looking forward--the distance between frame rivets, instead of being exactly 24 inches, is less by twice the distanve from heel of floor to center of rivet, and the mould must be moved up that amount. Where the water-tight plate floors come, the moulding side. of the frame is moved a distance equal to the thickness of the plate, as is also one center keelson stiffener, the rivet spacing is lessened for water-tight- ness, and extra holes put in on outside strakes of bottom plating for the wide liners. At the belt floors, the small bracket connecting the longitud- inal stiffener to the channel seam strap shifts the stiffener over by the thickness of the bracket and necessitates a liner of corresponding thickness between the stiffener and the floor. And wherever a butt comes in an ad- joining member, requiring different spacing of rivets, these must be al- lowed for. In all such cases, "space moulds" covering only the particular frame space in which the change is necessary, are applied after the re- mainder of the member has been laid out from the regular mould. It is evident, therefore, that a very large amount of material, both plate and shapes, sufficient to build almost the entire water bottom of the ship for the straight midship body, and a considerable part of the material for some distance forward and aft of same, can be gotten out rapidly, from a very small number of moulds, ready to go into place, before the keel is laid. eee The practice of the Chicago yard, as of all other lake yards, is tu build the ship on level stocks and !aunch sideways. The keel blocks are now set, one to each keel plate, by a surveyor's level, and the center line put in 'by a transit instrument, the keel plates are strung along them, the' butt straps and liners bolted up and four tack rivets driven by hand in each strap to avoid possibility of shifting. Then one keel bar is put up, the center vertical keelson plates and butt straps, the other keel bar, keelson top angles and _ stiffeners and all carefully bolted and reamed. A large amount of work is thus ready for the pneumatic yoke riveters, which are then started and the whole keelson riveted and caulked water-tight. In the meantime the various parts composing the floors have been punched, assembled on a long line of skids extending from the stationary steam riveter, tested by the mould, bolted carefully and reamed by pneumatic drill and riveted. It will be noticed that of all these pieces--namely, the channel floor, center keelson bracket, bilge bracket, bilge frame, longi- tudinal stiffeners and clips--only one piece, the bilge frame angle, has any curve to it. This angle is bent cold between two collars temporarily bolted to the upper roll of the ship yard bending rolls, the bilge being made an arc of a circle to facilitate this rolling as well as that of the bilge strakes of the hull plating. For more than half the length of the ship, therefore, there is no furnace or forge work in any part of the water bottom except the few angle collars required to make water-tight work at the tank