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only of small area are of 10 lb. (4 in.) only, with 3 in. × 23 in. angle stiffeners. For the sides of magazines with teak lining 3-in. zeds were formerly used as the stiffeners.

The principal fore and aft bulkheads in a large ship are(i.) Middle line engine-room bulkhead.

(ii.) Inner coal-bunker bulkhead.

(iii.) Outer coal-bunker or wing bulkhead.

(iv.) Upper coal-bunker bulkhead.

These are all shown in Figs. 52 and 53. We have noticed that in some cases (Fig. 23) the two latter bulkheads have been omitted to increase the coal capacity and to make the transport of coal more easy.

(i.) Engine-room bulkhead.-This bulkhead extends for the whole length of the engine-room, and is taken to the height of the main deck. In battle-ships this is only necessary in the ventilators, etc.; but in large cruisers, where the protective deck has to be lifted to the main deck (Fig. 52), the bulkhead is carried right up to this deck. The bulkhead is carried to this height in order to prevent water flowing over the top in case one engine-room was flooded. It is important that this bulkhead should be amply strong in view of the severe strains that would come upon it if one engine-room were flooded. On this account it is of 12 lb. (in.), and constructed and stiffened in a similar manner to the main transverse bulkheads.

(ii) Inner coal-bunker bulkhead.-This bulkhead is well supported by the divisional bulkheads in the coal bunkers, and is not so strongly stiffened as in the previous case. The plating is lap-butted, lap-jointed, single-riveted; the two lower strakes are 12 lb. (in.), and the remainder 10 lb. (in.). The stiffeners are 5-in. zeds at each beam, connected above and to the inner bottom by bracket plates. Angles 3 in. x 2 in. are worked

between.

(iii.) Wing bulkhead. This bulkhead when fitted forms a virtual continuation of the inner bottom, and is formed of 15-lb. (3 in.) plating, stiffened the same as the inner bulkhead.

(iv.) Upper coal-bunker bulkhead.-This bulkhead, only being from deck to deck and not likely to have to stand any great pressure of water, is of 10-lb. (4 in.) plating, stiffened by angles 3 in. × 21⁄2 in. worked 2 ft. apart.

The beams of the ship run continuously through the longitudinal bulkheads, and in order to make the upper portion

watertight, angle bars are smithed to fit in the space between the beams, as Fig. 57. The riveting is closely spaced and the whole carefully caulked.

The bulkheads underneath barbettes are specially stiffened to efficiently support the barbette, etc.

Numbering of Bulkheads.-Transverse bulkheads are distinguished by the number of the frame station at which they come. Longitudinal bulkheads are distinguished by the numbers of the frames at which each begins and ends. Thus, bulkhead 116 to 140 would be the bulkhead extending between frames 116 and 140. Formerly bulkheads were distinguished by letters, but it has been found more convenient to use numbering instead.

Water-testing.-All watertight flats and bulkheads, outer bottom, inner bottom, and decks are tested for watertightness under water pressure. Wherever practicable, the compartments

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are actually filled with water, the head of water applied being about 5 ft. above the load waterline. Where this is not possible, the watertightness is tested by means of a hose. Usually one of the boiler-rooms and one of the engine-rooms are filled with water to a height of 5 ft. above the load waterline, in order to test the strength of the bulkheads, as well as the watertightness.

A large number of holes are necessary in a bulkhead for the purpose of connecting fittings, etc., to the bulkhead. It is important to note that if any such fittings are removed for any purpose, the holes left behind should be properly filled up again by a tap rivet. Otherwise the watertightness of the bulkhead is destroyed. The glands on bulkheads, where voice-pipes, electric wires, etc., pass through, should be periodically examined to see that the screws for attachment have not worked out.

An Admiralty circular has recently been issued, directing that

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one compartment is to be flooded in each ship at least once a year, to test the watertightness of the bulkheads, doors, etc. (see S. 32111/1903, January 29, 1904).

Watertight Doors.-The transverse and longitudinal bulkheads being watertight, it is necessary that openings in them should be capable of being made watertight. These openings are made as few in number as possible, but still a number of

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the most important bulkheads have to be pierced by doors, which must be open for passage through, even supposing the ship to be in action. Such bulkheads are

(a) The divisional bulkheads between the engine and boiler

rooms.

(b) The coal-bunker bulkheads.

(c) The bulkheads at the ends of ammunition passages.

Watertight doors are of three kinds, viz. hinged, vertical sliding, and horizontal sliding.

Hinged Doors.-This type of door is the most common in H.M. ships, being fitted to the less important bulkheads below water, and to nearly all the watertight bulkheads above water. (In a few cases above water, a hinged door would be inconvenient, and a sliding door is fitted, as in the upper-coal bunkers.) No provision is made for closing these hinged doors from above, they must be closed at the door itself.

The opening made in the bulkhead is stiffened round by an angle bar frame (Fig. 58). The door is formed by a piece of plate of the same thickness as the bulkhead; this also has a stiffening bar round the edge. In "Mechan's" patent door this stiffening is obtained by embossing the edge to the shape shown, giving us a lighter door. India-rubber is worked all round the edge of the door as shown, which engages with the stiffening bar on the bulkhead. The door is forced home to the rubber by means of handles, each of which presses against a wedge-shaped piece of metal on the door. Spring clips are placed to keep the handles away from the door when not in use. The hinges are made with an elongated hole for the pin, so that a certain amount of play is allowed to force the door home. The handles pass through a metal collar on the bulkhead, and watertightness is obtained by a leather washer. The india-rubber on the door, when perished, can be readily removed by means of the securing strips, which

screw into the door. This india-rubber must never be painted or greased. It should be chalked to prevent sticking. The leather washers on the door clips should be periodically examined. No tread over the sill should be allowed, which will prevent the door from closing.

Vertical Sliding Doors.-These doors are fitted to bulkheads where it is necessary to close from above, and where sufficient head room is possible above the opening to take the door when open. They are of two kinds-(1) ordinary, and (2) quick closing. These latter are fitted on the bulkheads between the engine and boiler-rooms. Quickclosing doors were formerly fitted with balance weights, to render the closing easy and quick. Now, however, a coarse thread of large diameter is used on the spindle. For ordinary doors a

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FIG. 59.

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