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The present chapter deals with the methods adopted in ships of the Royal Navy for clearing water out of the ship, which has entered through damage or has accumulated in the bilges under the ordinary conditions of working; and also the means for voluntarily admitting water into certain portions of the ship to preserve stability, or to keep the ship upright or on an even keel after damage, or to flood the magazines, etc., in case of fire.

By Drainage is meant the means of allowing water to pass from one compartment to another until it reaches a pump-suction by which it can be removed.

By Flooding is meant the deliberate admission of water into the ship through a sea-cock. This may be necessary to correct heel or trim after damage, or in the event of fire.

By Pumping is meant the general arrangements adopted to remove water from the ship by means of the fire and bilge pumps in the engine-rooms, or by the Downton pumps, worked by manual power.

Before dealing generally with the subject, it will be advisable to see how far the pumps fitted to a ship are able to deal with the inflow of water.

If A be the area of a hole in a ship's bottom in square feet, and d the distance of the centre of the hole below water, then the initial velocity of the water through the hole is given by 8Jd ft. per second, so that every second there would be SA^fd cubic ft. of water entering, or about HA^dtons per minute. If the hole is 16 ft. below the surface, about 50 tons will enter in a minute for every square foot of area.

The following is the specified capacity in tons per hour of the pumps available for dealing with such a leak in a recent large ship, viz.—

Four centrifugal pumps (used ordinarily for circulating"! water through the condenser drawing from the sea), J- 5600 tons
which can draw from the engine-room bilge J

Four fire and bilge pumps 400 tons

Four Downton, pumps 100 tons

6100 tons

That is about 102 tons per minute. But we have seen above that the water through 1 square ft. amounts to 56 tons a minute, so that a hole only 2 square ft. in area (19 in. diameter), 16 ft. below surface, is sufficient to overpower the whole pumping capacity of a large ship. Such a hole is small in comparison with what would result from a collision, and this illustrates the importance of efficient watertight subdivision, which has been dealt with in previous chapters. By this means the damaged compartments may be isolated, and a collision mat placed in position over the hole so that repairs of a temporary nature may be undertaken.

In recent ships the arrangements for pumping and drainage are considerably simpler than formerly adopted; it is proposed only to deal with the arrangements in a battle-ship of the Duncan class, as being typical of recent practice.

Main Drain.—Special arrangements are made for clearing the ship of large quantities of water for which the ordinary steam and hand pumps would be inadequate. For this purpose a main drain (Fig. 91) is worked above the inner bottom from the forward boilerroom, branching to either engine-room. This drain is 15 in. diameter in the middle boiler-room, and 20 in. x 15 in. in the after boiler-room. By means of this drain, water can be passed from either boiler-room into one or both engine-rooms. Sluice valves, with non-returns, are fitted as shown to control the flow of water to the engine-rooms; the non-return valves automatically prevent the passage of water from the engine-rooms or from one boiler-room to another. In each engine-room, suctions are taken down from the circulating pumps of the condensers, so that these pumps can be made to draw from the engine-room bilge if desired instead of from the sea. These circulating pumps work independently from the main engines, and their engines are placed as high in the engine-rooms as possible, in order that they may continue working even if the engine-room is flooded to a considerable depth. The sluice valves on the main drain are worked from below and also from the main deck.

In addition to the main drain, the forward compartments likely to have large quantities of water are drained into the forward


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boiler-room (Fig. 91). Similar drains are fitted aft, draining into the engine-rooms. At the forward end we notice that two pipes, 8 in. diameter, are used, and into these we have pipes leading from barbette, submerged torpedo-room, torpedo-tubes, chain lockers, etc. The forward and after drains, and also the main drain, each have connection to a sea valve for flushing purposes. The wing

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Fia. 93.—Pumping section.

compartments and inner coal-bunkers are drained on to the top of the inner bottom, as shown in Figs. 91 and 93.

When a flat requires draining, a valve, as Fig. 99, is fitted. Above the flat there is a strainer with screw-down valve, and below the flat a flap valve to act as non-return.

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