ENGINES.

BOILERS.

BOILERS

BOILERS

FORECASTLE

SECTION.

CHAPTER VI.

WATERTIGHT BULKHEADS, DOORS, ETC.

THERE are four main methods of watertight subdivision, viz. by means of

(i.) A watertight inner bottom with watertight vertical keel, longitudinals, and frames;

(ii.) Watertight decks and flats;

(iii.) Transverse bulkheads; and
(iv.) Longitudinal bulkheads.

We have already dealt with the first two of these. The valuable feature of a double bottom has to be dispensed with in small vessels on account of the space thus occupied. In all ships, however, we get watertight subdivision from the last three of the above (see Figs. 52 and 54).

We now deal with the bulkheads. These are not only useful, in dividing the ship into a number of watertight compartments, but they form a most valuable addition to the ship's structural strength.

Transverse Bulkheads.-These are watertight partitions which go transversely across the ship. Fig. 52 shows the large number of such bulkheads fitted in a large cruiser; Fig. 54 is for a small cruiser. The one nearest the stem, extending to the upper deck, is the collision bulkhead, and many instances have occurred, especially in merchant vessels, in which, after collision, this bulkhead has remained intact and saved the ship from possible foundering. On account of its importance it is well stiffened, and in recent ships no openings of any kind are allowed in it. Any access required to the forward side must be by means of scuttles through the decks, and if the forward space does require draining, it must be pumped out by means of a hose.

In some recent battle-ships an additional bulkhead is fitted 3 ft. abaft the collision bulkhead. This is termed the "cofferdam"

bulkhead, and the 3 ft. space thus formed is intended to be packed, like an ordinary cofferdam, before ramming, to limit the flow of water aft, supposing the collision bulkhead to be damaged (see Fig. 67).

A governing feature in the construction of any bulkhead is the area and depth of unsupported plating likely to be exposed to water pressure. The transverse bulkheads forward and aft of the machinery spaces are well supported by the decks and flats, and so do not require any extensive stiffening, as the unsupported area is not great. Such bulkheads are usually formed of 10-lb. (4 in.) plating, stiffened with angles 3 in. x 21 in., worked vertically, the spacing varying from 2 to 2 ft. The plating is lap jointed at edges and butts, and single riveted. Bulkheads forming the sides of magazines in which teak lining is fitted are stiffened by

zed bars 3 in. deep. In the most recent ships, however, this is not necessary, because of the omission of the lining to magazines.

The collision bulkhead is formed of 15-lb. (3 in.) plating, stiffened by 5-in. zeds and 3 in. × 2 in. angles spaced alternately 2 ft. apart. Above the protective deck the angles only are fitted.

The transverse bulkheads forming the divisions between the engine and boiler-rooms are specially constructed and stiffened because of the very large area and depth of unsupported plating. (In one case 46 ft. wide and 25 ft. deep.) The plating is 15 lb. (3 in.), worked flush jointed, the horizontal joints being covered with a tee bar 4 in. × 5 in. forming the edge strip. The vertical joints are covered with single-riveted butt-straps on the opposite side to the tee bars. The main stiffening is worked vertical, and is formed of 5-in. zeds every 4 ft., with 3 in. × 2 in. angles between. At intervals of about 8 or 12 ft. the zeds are replaced by I bars 12 in. x 6 in. x 6 in., worked on both sides of the bulkhead, the tee bars being cut and connected to them (Fig. 55).

Both the zed and I bars are well supported at the head and heel by bracket plates. This extensive stiffening has been found necessary to enable the bulkheads to withstand the great pressure that would exist supposing one of the adjacent compartments filled with water. It is the practice in each ship while building to actually fill a boiler-room with water to a height of 5 ft. above the load waterline, in order to test the strength of the bulkhead. The safety or control of a ship might very conceivably depend on one of these main bulkheads remaining intact if an engine-room or boiler-room were flooded.

The bulkheads forming the fore end of the fore boiler-room and the after end of the engine-room do not need this extensive stiffening, because of the support received from the decks and platforms. In these cases the 12-in. I stiffeners are not fitted.

The transverse bulkheads in way of the inner bottom are bounded thereby, and the watertightness is continued to the outer bottom by means of the watertight frames already considered.

Between the main transverse bulkheads, divisional bulkheads are fitted in the side upper and lower bunkers, as seen in Fig. 52. Beneath the watertight flat in the upper bunkers of battle-ships, shown in Figs. 12 and 13, a further set of bulkheads is fitted between the above, thus giving most minute subdivision to the side in the neighbourhood of the waterline.

The fore-and-aft longitudinals, vertical keel, etc., are worked continuously through all the transverse bulkheads in order to

BULKHEAD
PLATING

-OUTER

Воттом

maintain continuity of the longitudinal strength. Where the longitudinal takes the form of a zed and angle, as at the ends of a ship, the watertightness is secured by working angle collars round, as shown in Fig. 56.

It will be noticed in Figs. 52 and 54 that a number of the bulkheads are carried right up to the upper deck. This is important in view of the sinkage, heel, and change of trim that might ensue after damage. The bulkheads being carried well above water, there is more likelihood of confining the water on one side.

FIG. 56.

Longitudinal Bulkheads.-There are a number of small longitudinal bulkheads forming the boundaries of magazines, etc. These assist in maintaining the watertight subdivision, but being

only of small area are of 10 lb. (4 in.) only, with 3 in. x 24 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. (6 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 33 in. x 23 in. worked 2 ft. apart.

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