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 a small thickness of teak backing is fitted, of minimum thickness, 2 in., to form a bed for the back of the armour. Formerly the skin plating behind armour was in two thicknesses, but the present practice is to work this plating 1 Omitted in recent ships (see Fig. 13).

FIG. 143.

FIG. 144.--Support to 6-in. armour.

3

in one thickness of in. or å in. 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 UPPER DECK. 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 framing behind armour in recent ships is formed of two 10 in. by 3 in. angle bars worked back to back and connected by a single riveted lap, shown in Fig. 18A. The battery armour is backed and supported by MAIN DECK. framing. Barbettes, although

well fitted to withstand blows

by their shape, are supported
inside the double thickness of
plating by closely spaced ver-
tical girders.

No backing is now employed
behind the armour plating of
barbettes, and in order to further
diminish the diameter of the
MIDDLE DECK. barbette the framing and plating
is stopped some distance from
the top (see Fig. 144A). The
reduction of diameter thus ob-
tained has resulted in a con-

PLAN AT C.D. siderable economy in the weight
of armour. Adjacent plates in
the
tier are connected
together by a butt-strap at the
upper part and also by keys.

FIG. 144A. Sup-
port to barbette

armour,

upper

OF 19 LBS. EACH.

TWO THICKNESSES

Behind armour, where men are likely to be employed in action, the inside of the framing is covered in with 10-1b. plating (see main deck in Fig. 13). When armour is struck, rivets are likely 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).

Armour Bolts.-With wrought-iron armour, the bolts for securing the armour to the ship's structure were carried right

through with a large conical head flush with the surface of the armour. With hard-faced 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.

FIG. 116.

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 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. When no backing is fitted to barbettes the bolt is fitted as shown in Fig. 147A.