446

mSHOLLS'S  SEAMANSHIP  AND  NAUTICAL  KNOWLEDGE

single riveted butt straps, also double and treble riveted butts as shown
in Figures 28 and 29.

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	╗ХХ"ХА>Х
 Х   Х   Х   o
	o    o    o


	0     л     O     O
	

0     0
	+     *     Х     0
	000

Fig.  29ЧTreble Riveted Butt.

The ends of angle bars are joined by means of a  "bosom" piece, or
short piece of angle bar fitting closely into the angles and of sufficient

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x* - - J* - Х /' T - -r- л Ч -^

Figt 30. Ч A Bosom Piece.

length to take at least three rivets in each row on each side of the joint
as shown in Figure 30.
SHELL PLATING.
The system of shell plating now almost universally adopted
is the "raised and sunken" strake system (Figure 31), the outer plates
being sometimes "joggled" as in Figure 32. A "strake" of plating is
a line of plates.
Raised and Sunken Plating. Ч In Figure 31, A is the frame, B is the
sunk strake of shell plating resting solid against the frame, C is the
raised strake each edge of which overlaps and rests on the edges of the
adjacent sunk strakes. The overlap at E is called the plate "landing,"
and D is called the "sight" edge of the raised strake; the sight edge of
the sunk strake would be seen from the inside of the ship. 2? indicates
the position of a narrow parallel "liner" or packing' piece of the same
breadth as the flange of the frame; it is inserted to form a solid foundation
for the raised strake to rest against. The landings of shell plating are
always "chain" riveted, that is, the rivets are exactly opposite to each
other as distinguished from "zig-zag" riveting. (See Figures 26 and 27.)