Imágenes de páginas
PDF
EPUB

cruiser shown in Fig. 28 is generally 123 lbs.

6

(16 in.). In way of the engine-room, however, it is 17 lbs. (1 in.), to stiffen the ship in way of the fast-running machinery. The flat keel and sheer strake, next the upper deck, are both 20 lbs. (3 in.). These are both reduced to 17 lbs. beyond the half length.

Plating of Sloop.-The bottom plating of the sloop shown in Fig. 30 is generally of 10 lbs. (4 in.), with flat keel and sheer strake of 15 lbs. (3 in.).

Plating of Destroyer.-For this type of vessel high tensile steel is used for the outer bottom plating in the more recent ships. The flat keel in Fig. 32 is 36 in. x 10 lbs. (in.), sheer strake 30 in. × 8 lbs., the remainder of the plating being 61 lbs.

[ocr errors]
[graphic]
[blocks in formation]

FIG. 53.--Watertight subdivision, first-class cruiser.

[blocks in formation]

FIG. 54.-Watertight subdivision, third class cruiser.

HOLD

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 "

[ocr errors]

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. (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

[ocr errors][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small]

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. (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. (in.), worked flush jointed, the horizontal joints being covered with a tee bar 4 in. x 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 34 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

« AnteriorContinuar »