Stability (GM) Calculator
Estimate metacentric height and initial stability
Stability Results
Metacentric Height (GM)
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Stability Assessment
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BM (Metacentric Radius)
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KB (Keel to Buoyancy)
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KG (Keel to Gravity)
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KM (Keel to Metacenter)
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Righting Moment at 1 deg
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Roll Period (estimated)
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GM Guidelines
| GM Range | Stability | Motion |
|---|---|---|
| < 0 | Unstable! | Will capsize |
| 0 - 1 ft | Tender | Slow, comfortable roll |
| 1 - 2 ft | Moderate | Balanced motion |
| 2 - 3 ft | Stiff | Quick, snappy roll |
| > 3 ft | Very Stiff | Can be uncomfortable |
Understanding Stability
Stability Terms
GM: Distance between center of gravity (G) and metacenter (M). Positive GM = stable.
BM: Metacentric radius - depends on hull shape.
Formula: GM = KB + BM - KG = KM - KG
Factors Affecting GM
Lower center of gravity increases GM (more stable)
Wider beam increases BM (stiffer)
Free surface effect (liquids) reduces effective GM