Sailboat Stability Calculator

The sailboat stability calculator evaluates key seaworthiness metrics including the Capsize Screening Formula (CSF) and Brewer's Motion Comfort Ratio (MCR). Input your vessel's dimensions to evaluate its suitability for bluewater passage making versus coastal cruising.

Imperial (Feet / Lbs) Metric (Meters / Kg)

Understanding Sailboat Stability Ratios

Naval architects utilize screening formulas to evaluate a sailboat's ocean-going safety and motion comfort characteristics without needing complex towing tank tests or hydrodynamic simulations.

1. Capsize Screening Formula (CSF)

Developed by the Ocean Racing Council (ORC) following the tragic 1979 Fastnet Race, CSF measures a vessel's vulnerability to capsize from breaking waves:

CSF = Beam / (Displacement in cu ft)1/3

  • Less than 2.0: Ocean Capable. Lower values indicate better ultimate stability and resistance to capsize in heavy offshore seas.
  • Greater than 2.0: Coastal / Light Displacement. Typically disqualified from major offshore ocean races due to higher capsize risk.

2. Motion Comfort Ratio (MCR)

Created by yacht designer Ted Brewer, MCR predicts how gentle or harsh a boat's motion will feel in heavy seas:

MCR = Displacement / [ 0.65 × (0.7 × LWL + 0.3 × LOA) × Beam4/3 ]

  • Under 20: Lightweight coastal racers / day sailors (quick, snappy motion).
  • 20 – 30: Modern coastal cruisers.
  • 30 – 40: Moderate offshore bluewater cruisers.
  • Over 40: Heavy displacement, traditional ocean passage makers (very gentle roll).
Source: onlysuperyachts.com/calculators/sailboat-stability-calculator/