Capsize Screening Formula (CSF)
What is Capsize Screening Formula (CSF)?
The Capsize Screening Formula is an attempt to validate if a given yacht is suitable to participate in an ocean race.
Such validation became obvious after the Fastnet race in England in 1979 was hit by a storm that shredded the race fleet.
Of 303 yachts, 85 finished, 75 capsized, and five sank. 15 yachtsmen died.
*) The Rating Limit is not the length of the yacht but is closely correlated to the length. The smallest yacht in the race were 28 ft.
On this background the Cruising Club of America came up with the Capsize Screening Formula below.
| Class | Rating Limits* | Started | Finished | Retired | Crew lost | ||
|---|---|---|---|---|---|---|---|
| 0 | 42.1 | - | 70 | 14 | 13 | 1 | - |
| I | 33 | - | 42 | 66 | 36 | 19 | - |
| II | 29 | - | 32.9 | 53 | 23 | 30 | - |
| III | 26.6 | - | 28.9 | 64 | 6 | 62 | 6 |
| IV | 23 | - | 25.4 | 68 | 6 | 44 | 6 |
| V | 21 | - | 22.9 | 68 | 1 | 48 | 3 |
| Total | 303 | 85 | 194 | 15 | |||
On this background the Cruising Club of America came up with the Capsize Screening Formula below.
How to calculate the Capsize Screening value?
Capsize Screening Formula (CSF)
| Abrev. | Unit | Description |
|---|---|---|
| Beam | ft | Greatest beam measured |
| Displacement | lbs | Displacement of the boat in pounds |
| 64 | n/a | Conversion factor: The weight of 1 cubic feet of sea water is 64 lbs |
The capsize screening value should be less than or equal to 2 for ocean passages. Values greater than 2 are for coastal cruising use only.
Note: the Capsize Screening Formula is disputed by many, and the Cruising Club of America themself characterizes the formula as "rough".
| Boat | CSF value | Evaluation* |
|---|---|---|
| Malö 45 | 1.70 | yes |
| Contessa 32 | 1.76 | yes |
| Swan 46 | 1.85 | yes |
| UFO 34 | 2.01 | no |
| First 27 | 2.20 | no |
Other capsize indicators
There are some better indicators of a vessel’s likelihood of capsize.
Angle of Vanishing Stability
STIX: The EU developed its own stability index called STIX[2], a series of formulas which considered a wide range of factors and provides a reasonable sense of how a boat might perform in extreme conditions. Unfortunately meaningful results require a lot more information than most folks have access to for any specific design.
Angle of Vanishing Stability
STIX: The EU developed its own stability index called STIX[2], a series of formulas which considered a wide range of factors and provides a reasonable sense of how a boat might perform in extreme conditions. Unfortunately meaningful results require a lot more information than most folks have access to for any specific design.
References
[Ref 1]: 1979 FASTNET RACE INQUIRY REPORT by Sir Hugh Forbes, Sir Maurice Laing, Lieutenant-Colonel James Myatt. Printedby T. H. Brickell & Son Ltd,TheBlackmorePress, Shaftesbury, Dorset.
[Ref 2]: ISO 12217-2 Small craft — Stability and buoyancy assessment and categorization
[Ref 2]: ISO 12217-2 Small craft — Stability and buoyancy assessment and categorization