Sailboat Capsize Screen Factor Calculator
Calculate the offshore capsize screening factor for any monohull sailboat from beam and displacement.
Boats under 2.0 are considered offshore-capable by ORC standards.
The Capsize Screening Formula (CSF) is a simple measure of a monohull sailboat tendency to capsize in breaking seas.
It was developed after the disastrous 1979 Fastnet Race, in which 15 sailors died and 24 boats were lost or abandoned, largely due to repeated capsizing in breaking waves.
The formula:
CSF = beam_meters / displacement_cubic_meters^(1/3)
Where displacement is calculated from the mass: displacement_cubic_meters = displacement_kg / 1025 (seawater density)
A boat with a wide beam relative to its displacement has a high CSF — it is relatively easy to knock down and slow to self-right.
A heavy, narrow-beamed offshore cruiser has a low CSF — harder to capsize, quicker to recover.
The ORC (Offshore Racing Congress) standard:
- CSF below 2.0: Suitable for offshore ocean racing and bluewater cruising
- CSF 2.0 to 2.5: Coastal passages in moderate conditions; not recommended for offshore in severe weather
- CSF above 2.5: Racing or coastal use; capsize risk significant in breaking seas
Most production coastal cruisers fall in the 2.2-2.4 range — fine for the types of conditions they are designed for, but not appropriate for passages through potential storm zones.
Classic bluewater cruisers (Cape Dory, Hallberg-Rassy, Westsail) typically score 1.6-1.8.
Many modern wide-beam cruisers and racers score 2.4-2.8.
The CSF is a useful screening tool, not a complete stability analysis.
It does not account for ballast ratio, center of gravity height, sail area, or the full stability curve.
A low CSF is necessary but not sufficient for offshore safety — stability curve analysis (capsize angle, range of positive stability) provides a more complete picture.