438 NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

vessel. The gar board strakes are next in thickness to the sheer strake,
the thickness of the others being varied slightly. The extreme thickness
of the various strakes is maintained for half the midship length of the
ship and thinned off towards the ends. In shipyard practice the
strakes of plating are lettered A, B, C, etc., from the keel upwards and
the plates in each strake are numbered from aft forward; thus
shell plate C 12 is the third strake up from the keel and the twelfth
plate from the stern.

Mclntyre Tank.—Figure 19 represents the formation of a "Mc-
lntyre" tank. It is really a superstructure placed on top of a ship's
ordinary floors when water ballast is earned for only a portion of the
length of the ship. The Mclntyre system was the forerunner of the
cellular double bottom method of providing water ballast space.

A is a centre plate keelson with a^ indicating the stiffening and
connecting double angles at its upper and lower edges, and Og the
lug piece to get- an extra rivet connection to the floor.

Fig. 19.—A Mclntyre Tank.

. B is an intercostal centre plate fitted between the floors. It is
connected''to the floor plate by means of a short vertical angle 6, and
its lower edge is riveted to the "flat" plate keel by means of the short
fore-and-aft intercostal angle 52.
C, C, C and 0 are longitudinal plates standing vertically on top of
the floors and connected to the reversed frame by the continuous
fore-and-aft angles Cg, % and lug piece <?4. The top edge of the plate
is stiffened with a continuous angle bar c^ to which the tank top plating
E is riveted. F indicates the floor plate.
Watertight connection at the bilge is obtained as follows:—The
flame is cut at d, D indicates the "margin" plate. It extends fore and
aft the whole length of the tank; its upper edge is flanged at £> and
riveted to the tank top plating, its lower edge is riveted to fehe bilge
*strafce by means of a continuous fore-and-aft angle d.