BULKHEADS

457

Pillars are fitted in the deep tank between the centre line division and
the ship's side to prevent the deck from buckling under the stresses
which may be set up by the swishing of the water in a slack tank when
the ship is in a seaway. Sometimes specially deep tank girders are
substituted for pillars in order to get a clearer space for cargo. The
girders are connected to the deck beams and when they are deep enough
they serve as wash plates in lieu of the centre line division. Deep tanks
are fitted with watertight hatches, one on each side of the centre division,
the steel plate cover of the hatches being clamped and screwed down

ft

DOUBLE BOTTOM.
Fig. 45.

CELLULAR DOUBLE BOTTOM.

Fig. 46.

DEEP TANKS 'AND
CELLULAR DOUBLE BOTTOM.
Fig. 47.—Note the Small Watertight Hatches in 'Tween Decks.
tight on their coamings with screw bolts and made effectively watertight
by packing. See also page 603.
Various water ballast arrangements are shown in the foregoing
illustrations, the hatched lines indicating water.
HATCHWAYS.
Cargo Hatches in ships engaged solely in carrying cargo are made as
large as possible to facilitate rapidity in loading and discharging. These
large openings in the deck necessitate severing many of the beams,
thus reducing very considerably the transverse strength. Beanos are