well fitted to withstand blows by their shape, are supported inside the double thickness of plating by closely spaced vertical girders. Behind armour, where men are likely to be employed in action, the inside of the framing is covered in with 10-lb. plating (see to break and the heads to fly off, so that this lining forms some protection to men inside. This plating itself should be secured by screw rivets to the framing (see K, Fig. 9). FIG. 146. Armour Bolts. With wroughtiron armour, the bolts for securing the armour to the ship's structure were carried right through with a large Iconical head flush with the surface of the armour. With hardfaced armour, however, the surface must not be pierced for bolts because the surface would then be liable to crack badly from hole to hole when struck. Armour bolts are now screwed into the back of the plate (Fig. 145), and about one bolt to every 7 square ft. is allowed. Fig. 146 shows the holes in a specimen plate; it is important to have good security in order to keep fragments together, even if the plate is badly cracked. Experiments have shown that the pieces are still very efficient, provided they are held up to the backing. In order to diminish the liability of bolts breaking under the impact of projectiles, the shank of the bolt is made slightly less in diameter than at the bottom of the thread. The bolt will then stretch at this weakest part rather than break under the thread. A sleeve is fitted to provide sufficient length for this weakest is placed near the waterline, so that coal could be retained above, if desired, to obtain the protection which the coal affords. Armour Scuttles and Gratings.-In protective decks there are many openings for access, etc., which it would be necessary to FOR RAISING C FIG. 110. have closed in action to preserve the protection. These openings are usually closed by hinged covers having the same thickness as portion; also, to provide some elasticity to take the shock, the nut securing the bolt to the ship is fitted with an elastic washer of india-rubber. This is placed inside a "cup washer" to keep the rubber washer in place. In some places, as barbettes, it is not possible to get sufficient room for an ordinary armour bolt; in such places, the bolt, as in Fig. 147, has to be used. 4 |