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

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.

F

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

FIG. 59.

smaller thread of less pitch is used. Otherwise the construction of the doors is substantially the same (Fig. 60).

6

A cast-steel frame, shaped as shown in Figs. 59 and 60, is bolted to the bulkhead. The sides are formed, with a taper of in. to a foot, to correspond with the frame on the door. The door is formed of a steel plate, with a steel casting to stiffen it, shaped as shown. The section of the door shows very clearly the construction, and how the door jams in between the bulkhead casting and the check plate. The top edge of the casting is provided with a metal nut, with a thread to correspond with that on the spindle. This spindle extends from the top of the opening to the main deck, the thread, of course, extending only sufficient to open the door. The door can be closed by a set of gearing from below, as well as from above, and, when necessary for purposes of escape, it can be worked from either side of the bulkhead.

The doors between engine and boiler-rooms, and to coalbunkers, have their sills kept well above the inner bottom.

Horizontal Sliding Doors.-Doors of this type (Fig. 62) are fitted to important bulkheads below water (and to a few above

FIG. 61.

water), to which vertical doors cannot be fitted because of the lack of

sufficient head room. The opening in the bulkhead is bounded by a steel casting, shaped as Fig. 61. This casting is secured to the bulkheads by bolts. At the bottom and top there is a groove, having a taper of in. to a foot, in which the door slides, and in which the door jams when closed. The door is formed by a steel plate, well stiffened by a steel casting, shaped as shown. The weight of the door is taken by two wheels. The inside edge of the door has a gunmetal strip all round, which engages with the bulkhead casting. The leading edge of the door jams into a number of clips on the edge of the frame, and the following edge of the door has some back pieces, which jam against the back of the bulkhead frame. The door has two horizontal steel racks, and into these two gunmetal pinions engage, these being rotated by a vertical spindle. This spindle extends to the main deck, so that the door can be worked from above if desired.

The door can also be closed at the door by a spanner, working on a nut on the spindle.

A disadvantage with horizontal doors is the existence of the bottom groove. The dirt from the traffic soon fills up the groove,

FIG. 62.-Horizontal sliding watertight door.

and this gets hard and prevents the door from closing. To obviate this a sill plate is fitted over the sill. When the spindle for closing is first turned, it turns the sill plate up out of the way, to allow the door to slide along and shut. When the door is again opened, the sill plate automatically drops over the groove again.

The vertical spindles for closing watertight doors are always so arranged that a right-hand motion closes the door. The deck