row of rivets, to get a good connection and to allow the edge to be caulked. The edge riveting of the outer flat keel is double riveted with 1-in. rivets. The remainder of the riveting is in. diameter, as shown. The butt-straps are double riveted, and for the outside strakes extend from the longitudinals to the edge of the inside strakes. For the inside strake the strap extends the whole width of the plate.

The ordinary frames are connected to the outer bottom by -in. rivets spaced 7 to 8 diameters. For the watertight frames it is necessary to have the rivets closely spaced, viz. 4 to 5 diameters. This close riveting cuts away a lot of material from the outer bottom plating in one transverse section of the ship, and causes this section to be a distinct line of weakness. In order to compensate for this, a wide liner called a bulkhead liner is fitted to each outside strake instead of the ordinary liner. This wide liner forms a sort of strap over the weak place, and in this way the strength at the watertight frame can be brought up to an equality with that at an ordinary frame. In the case of the second strake from the keel in Fig. 46, it will be noticed that the watertight frame comes next to a butt-strap, and the strap is made wide enough to act as a bulkhead liner and butt-strap combined.

Fig. 46A shows a form of bulkhead liner adopted in some ships to economize weight. The outside strake is only pierced at every other rivet, so that the reduction of strength is not so great at the section, and the liner can be smaller than would otherwise be necessary.

The side plating above the protective deck is recessed back from the side of the ship to make room for the armour and backing (see Fig. 18). This plating is in two thicknesses, each of 20 lbs. (in.), for 9-in. armour. No butt-straps or edge strips are necessary for this plating, as each thickness acts as security to the edges and butts of the other thickness. Above the armour the plating is 20 lbs. (in.) to the upper deck, except where an armoured battery is worked between the main and upper decks, as Fig. 13, in which case the double thickness of plating is carried right up.

The side plating is doubled in way of any protective plating to form a flush surface. Thicker or doubling plates are also worked in way of the stem and sternpost, in way of hawse-pipes, and where necessary to take the chafe of anchors and cables, and

in other places where special local strength is required, as in wake of torpedo-tubes. Covering plates are worked at the lower and upper edges of the side armour, as Figs. 18 and 34, connected to the armour by tap rivets. The edges of these plates are caulked so as to make the joint at the armour watertight.

In some battle-ships and cruisers the topside above the upper deck is worked to the boat deck, forming a closed-in superstructure (see Fig. 22). This plating is not intended to take any structural strains, and the sides are severed by the gangway ports. The

plating of the boat deck is also severed, and a sliding joint is made as shown in Fig. 5.

Inner Bottom.-The inner bottom of a battle-ship is generally 15 lbs. (in.), with the middle line strake 20 lbs. (in.). This plating extends to the fourth longitudinal, and the inner skin is continued to the protective deck by means of the wing bulkhead, which is 15 lbs. It is most important that convenient access should be provided to all the watertight compartments of the double bottom, in order that the condition of the plating, etc., may be periodically examined. The best arrangement would be to have the two manholes at opposite corners of the compartment, so that the space might be well ventilated before entering. Owing, however, to the obstructions caused by the boiler bearers, etc., this

is not generally possible; an actual arrangement adopted in one ship is shown in Fig. 49. The manholes should be on raised coamings, with a hinged cover, secured by a number of butterfly nuts as shown in Fig. 48. In some cases a hinged cover cannot be obtained, owing to some obstruction, and in these cases the cover is connected to the coaming by a chain. A plug is fitted to the manhole cover to enable the compartment to be sounded when necessary. This plug is hollow, as shown in Fig. 48, with a small vent-hole at the side. When the plug is slightly unscrewed, this hole allows the air to escape when flooding, and will also show when the compartment is full. The plug can then readily be screwed up tight. It is very necessary that the air should be allowed to escape so that the tank may be completely filled. At

other places, as on watertight flats or bulkheads, where occasional access through is necessary for inspection, the edge of the hole is stiffened by a strip, and a portable plate is secured by studs as shown in Fig. 50.

We have already noticed that although the inner bottom proper ends about one-sixth the length from each end, yet a virtual inner bottom is obtained well to the ends by the watertight flats, etc.

These double bottom spaces are carefully tested for watertightness by filling with water, the pipe conveying the water giving a head of about 5 ft. above the L.W.L. If the test is not satisfactory, the defects have to be made good and the compartment retested.

Outer and Inner Bottom Plating of a First Class Cruiser,

This plating is arranged on the same principles as for a battle-ship, the thickness generally being somewhat less. Special attention, however, is paid to the structure at the keel and at the upper deck. Fig. 3 shows the structure at the keel of a cruiser whose ratio of length to depth is 124. This is shown in comparison with the structure at the keel of a battle-ship of greater displacement whose ratio of length to depth is only 9.4. It will be noticed that the

FIG. 51.-Sheer strake of cruiser.

vertical keel is deeper, and the outer flat keel is 45 lbs. (nearly 1 in.), as against 30 lbs. (in.) in the battle-ship. The middle strake of the inner bottom is 25 lbs. as against 20 lbs. in the battleship. Fig. 51 shows the sheer strake of this cruiser, i.e. the plate of side next the upper deck. It is of 25-lb. high tensile steel, and the butt-strap is 30 lbs., quadruple riveted.

The inner bottom plating of a large cruiser presents no special features, and the remarks made above apply in this case also. It has already been noticed that the wing bulkhead has been dispensed with in recent ships to give a greater coal capacity. Figs. 52 and 53 show the whole of the watertight subdivision of a large cruiser, in which it will be noticed that an inner skin is obtained well towards the ends by means of the flats, etc., to the magazines and store-rooms.

Plating of a Second Class Cruiser.-The outer bottom plating of the cruiser shown in Fig. 25 is generally 17 lbs. (in.). The flat keel is 25 lbs. (3 in.), and the sheer strake 25 lbs. The inner bottom is 12 lbs. (in.).

Plating of a Third Class Cruiser.-The bottom plating of the

STRINGER

SHEER

STRAKE