Figure 5-1. Initial Metacenter with Line
of Action Buoyancy Angled Away From 0
RIGHTING ARM. When the ship is upright, the water line is WL and the forces will act as shown in FIGURE 5-1.
When the ship is inclined, however, the water line becomes W1 L1, which changes the shape of the underwater body.
As a result, the center of buoyancy moves from B to a new position B1, and the weight and buoyancy no longer act in the
same vertical line. Examination of the figure will show that a righting arm or restoring moment is now present, which
tends to rotate the ship toward its original position. The distance GZ is the righting arm.
The ship in FIGURE 5-2 develops positive righting arms from e to C, that is, from 0 degrees to 71 degrees.
This series of angles through which the ship has positive righting arm is called the range of stability. It indicates the
extreme angle to which the ship can roll.
Figure 5-2. Stability Curve Indicating Maximum GZ