Page 68 - Introduction to Naval Architecture

FLOTATION AND STABILITY 55

free surface effects. If the ship does not return to its original position
when the inclining weights are restored it is an indication that a weight
has moved in the ship, or that fluid has moved from one tank to
another, possibly through a leaking valve. The number of people on
board must be kept to a minimum, and those present must go to
defined positions when readings are taken. The pendulum bobs are
damped by immersion in a trough of water.
The draughts must be measured accurately at stem and stern, and
must be read at amidships if the ship is suspected of hogging or
sagging. The density of water is taken by hydrometer at several positions
around the ship and at several depths to give a good average figure. If
the ship should have a large trim at the time of inclining it might not
be adequate to use the hydrostatics to give the displacement and the
longitudinal and vertical positions of B. In this case detailed calcula-
tions should be carried out to find these quantities for the inclining
waterline.
The Merchant Shipping Acts require every new passenger ship to
be inclined upon completion and the elements of its stability
determined,

Stability when docking or grounding
When a ship is partially supported by the ground, or dock blocks, its
stability will be different from that when floating freely. The example of
a ship docking is used here. The principles are the same in each case
although when grounding the point of contact may not be on the
centreline and the ship will heel as well as change trim.

Figure 4,19 Docking