Page 86 - Introduction to Naval Architecture

FLOTATION AND STABILITY 73

(1) The areas under the GZ curve shall not be less than 0.055 m rad
up to 30°; not less than 0.09m rad up to 40° or up to the
downflooding angle and not less than 0.03 m rad between these
two angles.
(2) GZ must be greater than 0.20m at 30°.
(3) Maximum GZ must occur at an angle greater than 30°.
(4) Metacentric height must be at least 0.15m.

Loading conditions
Possible loading conditions of a ship are calculated and information is
supplied to the master. It is usually in the form of a profile of the ship
indicating the positions of all loads on board, a statement of the end
draughts, the trim of the ship and the metacentric height. Stability
information in the form of curves of statical stability is often supplied.
The usual loading conditions covered are:

(1) the lightship;
(2) fully loaded departure condition with homogeneous cargo;
(3) folly loaded arrival condition with homogeneous cargo;
(4) ballast condition;
(5) other likely service conditions.

A trim and stability booklet is prepared for the ship showing all these
conditions of loading. Nowadays the supply of much of this data is
compulsory and, indeed, is one of the conditions for the assignment of
a freeboard.
Other data supplied include hydrostatics, cross curves of stability and
plans showing the position, capacity and position of centroids for all
spaces on board. These are to help the master deal with non-standard
conditions.

FLOODING AND DAMAGED STABILITY

So far only the stability of an intact ship has been considered. In the
event of collision, grounding or just springing a leak, water can enter
the ship. If unrestricted, this flooding would eventually cause the ship
to founder, that is sink bodily, or capsize, that is turn over. To reduce
the probability of this, the hull is divided into a series of watertight
compartments by means of bulkheads. In action, warships are expected
to take punishment from the enemy so damage stability is clearly an
important consideration in their design. However, damage is a
possibility for any ship.