Uses of Hydrostatic Pressure

Note: If you use inches in your computation, you must use them throughout; if you use feet, you must use them throughout. What is the pressure on 1 square foot of the surface of a submarine if the submarine is 200 feet below the surface? Using the formula: P= H x D P = 200 x 62.5 = 12,500 lb per sq ft Every square foot of the sub’s surface that is at that depth has a force of more than 6 tons pushing in on it. If the height of the hull is 20 feet and the area in question is between the sub’s top and bottom, you can see that the pressure on the hull will be at least (200 – 10) x 62.5 = 11,875 pounds per square foot. The greatest pressure will be (200 + 10) x 62.5 pounds per square foot. Obviously, the hull very strong to withstand such pressures. USES OF HYDROSTATIC PRESSURE = 13,125 has to be Various shipboard operations depend on the use of hydrostatic pressure. For example, in handling depth charges, torpedoes, mines, and some types of aerial bombs, you’ll be dealing with devices that operate by hydrostatic pressure. In addition, you’ll deal with hydrostatic pressure in operations involving divers. Firing Depth Charges Hiding below the surface exposes the submarine to great fluid pressure. However, it also gives the sub a great advantage because it is hard to hit and, therefore, hard to kill. A depth charge must explode within 30 to 50 feet of a submarine to cause damage. That means the depth charge must not go off until it has had time to sink to approximately the same level as the sub. Therefore, you use a firing mechanism that is set off by the pressure at the estimated depth of the submarine. Figure 10-1 shows a depth charge and its interior components. A depth charge is a sheet-metal container filled with a high explosive and a firing device. A tube passes through its center from end to end. Fitted in one end of this tube is the booster, a load of granular TNT that sets off the main charge. It is also fitted with a safety fork and an inlet valve cover. Upon launching, the safety fork is knocked off, and the valve cover is removed to allow water to enter. When the depth charge gets about 12 to 15 feet below the surface, the water pressure is sufficient to extend a bellows in the booster extender. The bellows Figure 10-1.-A depth charge. trips a release mechanism, and a spring pushes the booster up against the centering flange. Notice that the detonator fits into a pocket in the booster. Unless the detonator is in this pocket, it cannot set off the booster charge. Nothing further happens until the detonator fires. As you can see, the detonator fits into the end of the pistol, with the firing pin aimed at the detonator base. The pistol also contains a bellows into which the water rushes as the charge goes down. As the pressure increases, the bellows begins to expand against the depth spring. You can adjust this spring so that the bellows will have to exert a predetermined force to compress it. Figure 10-2 shows you the depth-setting dials of one type of depth charge. Since the pressure on the bellows depends directly on the depth, you can select any depth on the dial at which you wish the charge to go off. When the pressure in the bellows becomes sufficiently great, it releases the firing spring, which drives the firing pin 10-2