Hydrostatic calculations and ship stability form the foundation of ship safety. During your deck or engine oral exams, surveyors will expect you to draw and explain stability indicators instantly.
The Righting Lever (GZ) Curve
A GZ curve plots the righting lever (GZ) against the angle of heel. Key points to master include:
- Initial GM: Indicated by the slope of the curve at 0 degrees heel.
- Maximum GZ: The point of maximum righting energy.
- Range of Stability: The range of angles through which the ship has positive stability.
- Angle of Vanishing Stability (AVS): The angle where righting energy drops to zero.
Correcting for Free Surface Effect (FSE)
When liquid shifts in partially filled tanks, the virtual center of gravity rises (G moves to G1), reducing the GM. Always calculate and apply Free Surface Correction (FSC) to obtain the fluid GM before confirming stability safety.
