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Practical Ideas for the Engineer -- Raising Sunken Vessels--Watertight Bulkhead Doors--Condensor Tube Corrosion --Electric Propulsion of Vessels --Reinforcing Frame for Concrete Vessels S soon as peace is declared there A should be a great harvest of sunken vessels which can be raised to the surface. The improved meth- ods now available will permit of raising vessels from much greater depths than was formerly possible. Before the war the value of a ship and its cargo was on the average about $125 per ton. At present it is worth three times as much, If sunken vessels are only partially submerged, it is sufficient to close all openings in the hull and then pump out the vessel. If totally submerged, there are four processes: (1) To build a cofferdam over the vessel and pump out the water from it faster than wa- ter .enters--this method was employed for raising the Warkxure at Tahiti; (2) to build a tight cofferdam around the hull, then pump it out and repair the damage--this was the method used in raising the Marine and the Liperte, the latter of which was filled with pro- jectiles; (3) the water may be forced out of certain compaftments of the vessel by compressed air, but these compartments must first be rendered watertight; (4) the breach in the hull may be repaired temporarily by divers and then a cofferdam may be built over one of the hatchways and the water pumped out of the hull sufficiently to enable the vessel to be refloated--this was the method successfully adopted: in the raising of the Japanese cruiser Mrxasa--the work of the divers was done at depths of 40 to 65 feet of wa- ter. ---- Watertight Bulkhead | Doors In a paper recently presented before the Institute of Marine Engineers by Lieut. I. Toro, Chilean navy, he described a system of watertight doors, which are designed to provide ready means of communication from one compartment _to another. The door can be operated from either side. In this system a hole is cut in the bulkhead, giving entrance to a chamber of rectangular shape. The joint be- tween the chamber and bulkhead is made watertight. The chamber is large enough to enable two men to move about easily in its interior. Two openings are pro- vided, one on either side, each opening being fitted with a sliding door marked E in the accompanying illustration. The doors are operated by means of a rack and pinion gear which is actuat- ed by hydraulic power. The cylinder is shown at A. The piston rod is made integral with the rack B which in turn drives the pinions C and D communicat- ing the desired motion to the door through the rack E. The controlling PRESSURE ITO. OPEN,. PRESSURE TO OPEN ULKHEAD FROM r \FROM. ; mainy MAIN A _ TO EXHAUST 4 PRESSURE PRESSURE rr TO_ CLOSE; -- P, = P F F } B tt N 'N . (BES x pl x y (pees O}; ail | P ; (KO! Y it z HZ QE Y > x IiX5 OF ese SHUT} x x T v INSIDE CONTROLLING LEVER E E : COMPARTMENT ICOMPARTMENT NO.1 NO.2 RACK ON RACK DOOR os DOOR ELOOR WATERTIGHT BULKHEAD DOOR apparatus is simple, consisting of a lever T which operates the valve F. To pre- vent both doors being operated simultane- ously, locking bolts R are provided. Thus, one door always remains closed. The working system, by which men can go from one compartment to an- other, is as follows: The door at one side of the chamber is first opened by means of an outside controlling lever. This allows the man to gain admittance to the cell. The door is then closed by the inside controlling lever. When the door is properly closed, but not before, the opposite door can be operated. Under ordinary conditions, each door is controlled from its respective side. Under abnormal conditions, however, panic-stricken men might forget to shut the door of the safe compartment, thus preventing other people from escaping. To guard against this, an emergency arrangement is supplied which permits the controlling of the doors from op- 236 'tions open and shut. posite compartments. The lever § jp addition to being connected to the rock- ing lever that operates the locking bolt R is also connected to the arm Z which is pivoted on a shaft fitted in a water- tight and air-tight manner through the side of the chamber. To the outside end of this shaft is connected an arm which is fitted with a handle and an index which works between the posi- In this manner the 'possibility of leav- ing men locked in the compartment js eliminated. Condenser Tube Corrosion Longer life of condenser tubes is to be secured rather by selection of materials, and care in manufacture than by modification of operating condi- tions, according to H. L. H. Smith in the Electric Railway Journal. Apart from the corrosion of iron and _ steel and that of alloys: used in engineer- ing structures, the loss by corrosion of condenser tubes is one of the most serious troubles encountered in the application of alloys. A theory now favored concerning the cause of corrosion in condenser tubes is that it is due to local currents between neighboring parts of different microstructure. The rapid corrosion of muntz metal in, salt water may be attributed to the alpha and_ beta brasses acting as electrodes, with the salt solution as electrolyte. Admiralty metal is of a more homogeneous micro- structure and therefore less subject to corrosion, besides which the small per- centage of tin exerts a valuable but imperfectly understood protective influ- ence. There is a tendency to use alloys with more copper, up to 95 per cent, but pure copper is not likely to be used because, apart from its high cost, there: is risk of copper oxide being formed and entering into solution with molten copper during the manufacture of tubes. The cause of "season cracking" is considered to be electrolytic. Internal strains produce a difference of electrical potential between different parts of the apparently homogeneous metal, and moisture provides the electrolyte. With- out initial tensile stress "season crack- ing" does not occur. If initial tensile stress be existent there is sufficient lack of homogeneity on the surface to start Corrosion, and the intensified stress at