therefore, to flood a double-bottom compartment we have to open a number of valves (Fig. 95), viz. Kingston (K) valves A and 1, unlock and lift up valve 2, and also unlock and lift up the valve leading to the particular compartment. The book above-mentioned states from which Kingston each compartment is flooded.

The wing compartments are flooded direct from sea valves placed as shown in Fig. 91. It will be noticed that each pair of wings has a flooding valve. The trimming tanks forward and aft can also be flooded direct from the sea.

Special arrangements are made for flooding magazines direct from the sea. Usually one Kingston supplies a number of magazines, etc. Besides the valve at the Kingston a valve is placed at the magazine, both of these being locked valves, which must be deliberately released to allow flooding to take place. They can be worked from the main deck or at the valves as may be desired. For trial purposes the outer, valve would be first opened so that the connecting pipe would be filled. This valve is then closed and the magazine valve opened. The water which then enters can be caught in a bucket. Where a Kingston valve is used only for magazine flooding, it is only necessary to fit one locked valve close to the magazine in addition to the Kingston. Where a Kingston serves other purposes a valve must be fitted at the Kingston, so that it may be open without flooding the magazine floodingpipe (see Fig. 100). No means are provided for draining magazines.

Dry Dock Flood.-Fittings are also provided for flooding magazines when the ship is in dry dock. A pipe is taken, between the Kingston and the magazine (Fig. 100), to the upper deck, and fittings, to take hose connections, are placed on this pipe above the main and upper decks. In the event of fire, hoses could be taken from the dockyard and the magazines flooded. In recent ships the hoses from dockyard are arranged to connect on to the Kingston direct, by means of a fitting which can be secured to the Kingston opening when the ship is in dry dock.

Air Escapes. When flooding any closed compartment it is necessary to provide an escape for the air. Pipes are led from the crown of the compartment, as in Fig. 93, with plugs on the upper ends. These plugs, when unscrewed slightly, allow the air to escape, and when the compartment is full they can be readily screwed up again. Plugs are also provided on the manhole covers (Fig. 48).

The air escapes from the magazines are constructed with a

simple lift valve, as Fig. 101; the pipe is led well up above the crown of the magazine and bent round, with the end perforated. In ships in which the crown of the magazine is near the waterline, these air escape valves are provided with a spring to

LEATHER

MAGAZINE

NETTING

TOP

GRATING

cause them to lift easily under the

small pressure.

Fire Main (Figs. 102 and 103).— The fire main and its system of pipes is obviously a most important set of fittings in a war-ship. The fire main itself in a large ship is a copper pipe 5 in. diameter, running all fore and aft under the protective deck. It is connected in the engineroom with the fire and bilge pumps, stop valves being fitted to shut off the fore-and-after portions of the system as desired. The fire main system can be charged from the Downton pumps if required, but the connection is fitted with a non-return valve, so that the pressure in the fire main may not affect the Downton pumps. The fire main is not rigidly connected to the protective deck, but is either supported from bulkheads or from slings connected to the deck. Branches are taken from the fire main to each stokehold, to submerged torpedo-rooms, capstan engine-room, ammunition passages, etc., with connections at each place for attaching a couple of hoses.

FIG. 101.-Air escape to
magazine.

Rising mains are led at intervals to the upper deck, two of these are led up under protection inside the barbettes. Each rising main has a stop valve beneath the protective deck at its junction with the fire main, and these valves are placed in accessible positions so that they can be worked from below the deck if desired. They are also geared to work from above the deck. To most of the rising mains there is also a stop valve beneath the main deck, to shut off the pipe above that deck in the event of the pipe being damaged in action. Branches are taken from the rising mains for flushing w.c.'s, washing out ash-shoots, washing out barbette guns, etc. One-inch bib valves are placed on rising mains between middle and main decks, main and upper decks, and in ammunition passages for drawing off small quantities of water if desired.

CHAPTER X.

VENTILATION.

THE problem of the effective ventilation of a ship is a more difficult one than the ventilation of a building. In the case of a building, ventilation is assisted because the porous nature of the walls allows air to diffuse through, this diffusion being all the more effective as the difference of temperature within and without is greater. In the case of a ship, however, the conditions are quite different, and the impervious nature of the skin renders diffusion through impossible; ventilation must be obtained by the actual introduction of fresh air and the withdrawal of the foul air.

Ventilation can be either natural or artificial. By natural ventilation is meant supply and exhaust without the aid of fans. By artificial ventilation is meant that fans are used to draw pure air down to, or draw foul air away from, the space to be ventilated, or both. Natural ventilation is used for the ventilation of the 'tween deck spaces, and for the special cases of the coal-bunkers and spirit-room. Artificial ventilation is used for the other spaces below, as magazines, shell-rooms, store-rooms, etc.

For the 'tween decks cowls are used which can be turned to face the wind, the exhaust taking place through the hatchways, and in some cases through other cowls which can be turned away from the wind. The side-lights are also useful for ventilation purposes. For the spirit-room it is necessary to have an independent supply and exhaust, with cowls on the upper deck, as it is undesirable to have any connection between the spirit-room and any other system of ventilation which might communicate with a magazine.

Coal-bunker Ventilation.-The efficient ventilation of coalbunkers is of extreme importance, because of the gas that comes from the coal. This gas when mixed with air forms an explosive mixture, and if it is allowed to accumulate may cause serious