Imágenes de páginas
PDF
EPUB

is placed near the waterline, so that coal could be retained above, if desired, to obtain the protection which the coal affords.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][merged small]

Armour Scuttles and Gratings.-In protective decks there are many openings for access, etc., which it would be necessary to

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

have closed in action to preserve the protection. These openings are usually closed by hinged covers having the same thickness as

[graphic]
[merged small][ocr errors]

FIG. 138.-Armour, etc., H.M. S. Duke of Edinburgh.

is placed near the waterline, so that coal could be retained above, if desired, to obtain the protection which the coal affords.

[graphic][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][merged small]

Armour Scuttles and Gratings.-In protective decks there are many openings for access, etc., which it would be necessary to

[merged small][ocr errors][merged small][graphic][subsumed][subsumed]

the deck. In coal-bunkers, where access is not possible, the holes are frequently covered by a sliding scuttle. A sliding scuttle is shown in Fig. 139. The plate works like a vertical sliding door, except that the grooves are parallel and not tapered. The wedges W jam under the clips C when the scuttle is closed. The gearing is worked from a convenient position outside the bunker, and the scuttle and gearing is covered in, so that it can be opened when the bunker above is full of coal. The usual scuttle in the protective deck is hinged, as Fig. 140. In such a scuttle, however, fitted in a coal-bunker, access must be provided by a trunk so that the clips may be got at to secure the cover. Scuttles of a

[graphic][subsumed][subsumed][subsumed][subsumed][ocr errors][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][merged small]

similar nature are fitted to the torpedo hatches, etc. Scuttles which are provided for escape are fitted with a balance weight so that they may lift easily.

There are, however, a number of openings in these decks which must be open even when the ship is in action. Such are the funnel and ventilator openings, and in these are fitted armour gratings. Fig. 141 shows a specimen set of gratings in a ventilating shaft. The space is divided into a number of rectangular spaces by girders, and into each of these spaces one or more gratings is fitted, resting on angles as shown in the sketch.

For a 2-in. deck the gratings are 7 in. deep, in. thick, and the clear space between the bars is 2 in. The machinery and boilers down below are thus protected in some measure. Most of these gratings are prevented from lifting as shown, but some have to be hinged for access below, and these are fitted with balance weights to make the lifting easy.

Splinter nettings are provided below the armour bars over the engine-room, so as to protect the machinery from débris that might get through the armour gratings. The netting is about 12 in. below the gratings.

Cofferdams.-Around all openings in the middle deck which are necessarily open in action a dwarf bulkhead is carried some feet above the L.W.L. A similar bulkhead is run close to the upper coal-bunker bulkhead (see Figs. 12 and 22). The space thus formed, about 12 in., is termed a cofferdam, and into these cofferdams canvas, oakum, or other such material can be jammed down. to act as a leak stopper, and so limit the flow of water across the deck, supposing the sides and bulkheads pierced. This is the primary function of these cofferdams, but in many ships they are made rather wider, about 18 in., in order to allow bags and hammocks to be stowed.

Armour Backing and Supports.-In the early days of armour protection with plates of wrought iron, the wood backing was very thick, the object being to provide a support which should be somewhat elastic. This thick backing was continued to the Admiral class, in which the 18-in. armour had 15-in. backing behind. With modern plates, however, it has been found that the best results have been obtained with a perfectly rigid support, and for land fortifications granite has been used. This is manifestly impossible for ships on account of weight, but a massive system of framing is always provided behind armour, with a small thickness of teak backing, about 4 in., to form a bed for the back of the armour. In all cases the skin plating behind armour is in two thicknesses. Figs. 142 and 143 show the framing behind the 18-in. armour of the Royal Sovereign. The 4-in. steel above is supported by 6-in. zed bars. In Majestic the 9-in. armour has 15-in. plate frames worked every 24 in., with horizontal stiffening girders as Fig. 18. In Cressy the 6-in. armour is supported by 10-in. zed bars worked every 24 in., with a horizontal girder as shown in Fig. 144. The battery armour fitted in the latest ships is backed and supported by framing. Barbettes, although

« AnteriorContinuar »