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that the bolts may be placed zigzag, as in Fig. 42B, and not in one continuous line, as would be necessary with an angle bulb beam. When thus laid direct on the beam the bolts of the butt of deck plank would be too close if taken through the flange of the beam, and at each butt, therefore, a short piece of plate, having the width of the plank, is fitted to take the bolts (Figs. 42B and 43).

Planking is fastened to the steel deck or the beams by means The of galvanized iron bolts with round heads, as Fig. 44. heads are let in well below the surface of the deck, and the cavity is filled in with a wood plug called a dowel, well steeped in white lead. A hempen grummet is placed under the head, and the nut underneath has a plate washer and grummet (Fig. 43). All this is necessary to make the hole in the deck properly tight. It will be noticed that the neck of the bolt is square to prevent the bolt turning when the nut is being screwed up.

The edges and butts of deck planking are caulked to make

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the deck watertight. The edges and butts are left with a slight opening at the surface, as Fig. 43, and into this oakum is forced, filling the opening right down to the bottom of the seam. The top is then payed with pitch. When carefully done this caulking should make the deck properly tight.

Corticine. In the living spaces of the ship other than those mentioned above, no wood decks are fitted, but corticine, a thick linoleum, is laid direct on the surface of the steel deck. The steel deck has to be laid flush for this purpose, with edge strips on the under side worked between the beams. The upper deck of torpedoboat destroyers is also laid with corticine.

The corticine is secured to the deck by means of a solution of orange shellac and methylated spirit, and when secured the edges are stopped with putty. Round scuttles and exposed edges the corticine is secured in addition to the deck by galvanized iron strips screwed into the plating. For thin decks, as in destroyers,

these strips are secured to the plating by bolts with a nut below having a washer and grummet. Where heavy wear takes place on a steel deck covered with corticine, as at the foot of ladders, the corticine is covered with plates of ribbed iron.

Watertight Hatches. The hatches to ordinary flats and decks are fitted with a raised coaming and a steel cover with an indiarubber joint. This indiarubber should be periodically examined, and where perished should be renewed, as a defective cover may destroy the watertightness of a complete deck. Scuttles and armour gratings to thick decks are dealt with in Chapter XIII.

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CHAPTER V.

PLATING OF THE OUTER AND INNER BOTTOMS.

Outer Bottom Plating.-The weight of this plating forms a good proportion of the total weight of the hull structure. It is a most important portion of the structure, because it not only contributes largely to the structural strength, but it keeps the ship watertight. One advantage of forming this plating of mild steel has already been referred to, viz. the advantage of the ductility of steel as compared with iron. Steel ships have frequently grounded without making water, under circumstances in which an iron ship would have been in a serious condition owing to the rupture of the plating.

Shift of Butts.-An important point in connection with the longitudinal structure of any ship is the arrangement of a good

24. FEET

FIG. 45.-Shift of butts.

shift of butts. A butt must be a place of relative weakness, and the butts of the various portions of the fore-and-aft structure are arranged well clear of each other. Thus, for the outer bottom plating, it is laid down that butts are not to be closer together in

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the same frame space than two passing strakes. With plates as

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now worked, 20 ft. in length and over, there is no difficulty in considerably exceeding this condition.

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Thus, in Fig. 45, 24-ft.
plates are worked and
five passing strakes are
obtained. The same
principle has to be borne

in mind when arranging
the butts of the vertical
keel and longitudinals,
inner bottom, etc., so as

to avoid any weakness
of the structure in any
one frame space (see
Fig. 46).

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lbs. (in.) at the ends. The fore-and-aft rows of plating, called strakes, are riveted to one another by double riveted laps. The plating is worked on the raised and sunken system as shown in Fig. 47. At every frame in way of each outside strake a filling piece or liner is necessary to get good riveting between the frame and the plate. These liners are often lightened, as shown, by oval holes between the rivets. At the middle line an additional outside plate, 30 lbs. (-in.), is worked, called the outer flat keel, the inner plate being the inner flat keel (see Fig. 3).

Riveting in Outer Bottom.-Fig. 46 shows in some detail the arrangement of the riveting, etc., in the outer bottom plating near the middle line. The lower angles of the vertical keel are connected to the flat keels by 1-in. rivets, and as the vertical keel has to be watertight, these rivets on one side are closely spaced, viz. 4 to 5 diameters. On the other side a wider spacing, viz. 8 diameters, is all that is necessary. Close spacing is necessary for the watertight longitudinal, No. 2, and wide spacing for the non-watertight longitudinal, No. 1. The butt-straps of the inner and outer flat keel are treble riveted with 1-in. rivets, and extend from the keel angles to the edges of the plate concerned. The edge of the inner keel is connected to the outer keel by a single

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