430

NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

frames, stringers, deeper floors, etc., to enable the shell plating to resist
its tendency to flexibility when sub]ected to panting stresses

The concentration of heavy weight along the middle line of the
hold introduces a collapsing stress which tends to draw the two sides
of the ship together. This fact was made noticeable when sailing ships
loaded heavy cargoes such as nitrate in Chile, copper ore in Australia,
etc. The lower layers of such cargoes were usually stowed out to the
bilges and gradually narrowed m towards the middle line, leaving a
space between the cargo and the ship's sides as in Figure 9. The

Fig. 9.—Collapsing.

rigging invariably slackened when the vessel was loaded and had to be
tightened up by taking a turn or two of the box screws of each shroud
and backstay. The fact was usually noted in the chief officer's log
book as a reminder that the rigging had to be slackened back again
before the cargo was discharged, thus allowing the hull freedom to
resume its original shape.

Fig. 10 —Dry Dock Stresses.
The opposite effect is created .when a ship is in dry dock. The
weight of tixe hull on the keel blocks pushes the bottom of the vessel