Note: If you use inches in your computation, youmust use them throughout; if you use feet, you must usethem throughout.What is the pressure on 1 square foot of the surfaceof a submarine if the submarine is 200 feet below thesurface? Using the formula:P= H x DP = 200 x 62.5 = 12,500 lb per sq ftEvery square foot of the sub’s surface that is atthat depth has a force of more than 6 tons pushing inon it. If the height of the hull is 20 feet and the areain question is between the sub’s top and bottom, youcan see that the pressure on the hull will be at least(200 – 10) x 62.5 = 11,875 pounds per square foot. Thegreatest pressure will be (200 + 10) x 62.5pounds per square foot. Obviously, the hullvery strong to withstand such pressures.USES OF HYDROSTATIC PRESSURE= 13,125has to beVarious shipboard operations depend on the use ofhydrostatic pressure. For example, in handling depthcharges, torpedoes, mines, and some types of aerialbombs, you’ll be dealing with devices that operate byhydrostatic pressure. In addition, you’ll deal withhydrostatic pressure in operations involving divers.Firing Depth ChargesHiding below the surface exposes the submarine togreat fluid pressure. However, it also gives the sub agreat advantage because it is hard to hit and, therefore,hard to kill. A depth charge must explode within 30 to50 feet of a submarine to cause damage. That means thedepth charge must not go off until it has had time to sinkto approximately the same level as the sub. Therefore,you use a firing mechanism that is set off by the pressureat the estimated depth of the submarine.Figure 10-1 shows a depth charge and its interiorcomponents. A depth charge is a sheet-metal containerfilled with a high explosive and a firing device. A tubepasses through its center from end to end. Fitted in oneend of this tube is the booster, a load of granular TNTthat sets off the main charge. It is also fitted with a safetyfork and an inlet valve cover. Upon launching, the safetyfork is knocked off, and the valve cover is removed toallow water to enter.When the depth charge gets about 12 to 15 feetbelow the surface, the water pressure is sufficient toextend a bellows in the booster extender. The bellowsFigure 10-1.-A depth charge.trips a release mechanism, and a spring pushes thebooster up against the centering flange. Notice that thedetonator fits into a pocket in the booster. Unless thedetonator is in this pocket, it cannot set off the boostercharge.Nothing further happens until the detonator fires. Asyou can see, the detonator fits into the end of the pistol,with the firing pin aimed at the detonator base. The pistolalso contains a bellows into which the water rushes asthe charge goes down. As the pressure increases, thebellows begins to expand against the depth spring. Youcan adjust this spring so that the bellows will have toexert a predetermined force to compress it.Figure 10-2 shows you the depth-setting dials of onetype of depth charge. Since the pressure on the bellowsdepends directly on the depth, you can select any depthon the dial at which you wish the charge to go off. Whenthe pressure in the bellows becomes sufficiently great,it releases the firing spring, which drives the firing pin10-2
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