Ship Stability (GM) Calculator
Calculate the final Metacentric Height (GM) after loading or discharging weights.
Initial Conditions
Loading / Discharging Operations
Operation 1
Final Condition Input
Enter the final KM value from the ship's hydrostatic tables for the new final displacement of ... Tonnes.
**Note:** This calculator provides a stability estimation. KG refers to the Vertical Center of Gravity from the keel. KM is the height of the Metacenter above the keel. The final KM value must be accurately obtained from the vessel's official hydrostatic tables based on the final displacement. This tool does not account for Free Surface Moments (FSM). Always consult the ship's approved loading computer and stability booklet for official calculations.
About Ship Stability (GM) Calculator
Understanding Metacentric Height (GM)
Metacentric Height (GM) is a measurement of the initial static stability of a floating body. It is calculated as the distance between the center of gravity (G) and the metacenter (M). A positive GM means the vessel is stable and will naturally return to an upright position when heeled.
Critical Stability Formulas
1. Metacentric Height:
GM = KM - KG
2. Final Vertical Center (KG):
Final KG = (Initial Moment + Added/Removed Moments) / Final Displacement
3. Moment Calculation:
Moment = Weight (Tonnes) × KG (m)
Interpreting GM Results
- Stiff Ship (High GM): Large GM causes a vessel to return to upright very quickly, resulting in short, jerky rolling periods. This can be stressful for the crew and cargo lashings.
- Tender Ship (Low GM): Small GM causes a slow, sluggish rolling period. While more comfortable, if GM becomes zero or negative, the ship loses its "righting lever" and may capsize.
- Minimum Standards: Most international regulations (IMO IS Code) require a minimum GM of 0.15m for cargo ships at all times.
Safety Disclaimer
Actual ship stability is also affected by the "Free Surface Effect" of liquids in partially filled tanks. This calculator assumes a "Solid KG." For a true safety assessment, always apply the Free Surface Correction (FSC) to your final KG before determining the fluid GM.