Capsize screening formula
Encyclopedia
The capsize screening formula (CSF) is a somewhat controversial figure. It is defined for sailboats as:
CSF = Beam
/ (Displacement
/64.2)1/3
It came into being after the 1979 Fastnet race
in England where a storm shredded the race fleet. The Cruising Club of America
(CCA) put together a technical committee that analyzed race boat data. They came up with this formula to compare boats based on readily available data. The CCA characterizes the formula as "rough".
A lower value is supposed to indicate a sailboat
is less likely to capsize
. A value of 2 is taken as a cutoff for acceptable to certain race committees. However this is an arbitrary cutoff based on the performance of boats in the 1979 Fastnet race
. The CSF does not consider the hull
shape or ballast
location.
Any two sailboats will have the same CSF value if their displacement and beam are the same. As an example, one could have a light hull with 50% ballast
in a bulb at the bottom of an eight foot fin keel
, the other could have a heavy hull
with 20% ballast in a 2 foot (0.6096 m) full-length keel
. The stability characteristics of the two sailboats will be drastically different despite the identical CSF value.
CSF = Beam
Beam (nautical)
The beam of a ship is its width at the widest point. Generally speaking, the wider the beam of a ship , the more initial stability it has, at expense of reserve stability in the event of a capsize, where more energy is required to right the vessel from its inverted position...
/ (Displacement
Displacement (fluid)
In fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, as in the illustration, and from this the volume of the immersed object can be deduced .An object that sinks...
/64.2)1/3
It came into being after the 1979 Fastnet race
1979 Fastnet race
The 1979 Fastnet race was the twenty-eighth Fastnet race, a yachting race competition held since 1925, generally every two years. In 1979, it was the climax of the five-race Admiral's Cup competition, as it had been since 1957....
in England where a storm shredded the race fleet. The Cruising Club of America
Cruising Club of America
-History:It was launched in the winter of 1921-1922 by a handful of experienced offshore sailors interested in cruising and the development of the cruising type of yacht....
(CCA) put together a technical committee that analyzed race boat data. They came up with this formula to compare boats based on readily available data. The CCA characterizes the formula as "rough".
A lower value is supposed to indicate a sailboat
Sailboat
A sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in the size are not strictly defined and what constitutes a sailing ship, sailboat, or a...
is less likely to capsize
Capsize
Capsizing is an act of tipping over a boat or ship to disable it. The act of reversing a capsized vessel is called righting.If a capsized vessel has sufficient flotation to prevent sinking, it may recover on its own if the stability is such that it is not stable inverted...
. A value of 2 is taken as a cutoff for acceptable to certain race committees. However this is an arbitrary cutoff based on the performance of boats in the 1979 Fastnet race
1979 Fastnet race
The 1979 Fastnet race was the twenty-eighth Fastnet race, a yachting race competition held since 1925, generally every two years. In 1979, it was the climax of the five-race Admiral's Cup competition, as it had been since 1957....
. The CSF does not consider the hull
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
shape or ballast
Sailing ballast
Ballast is used in sailboats to provide moment to resist the lateral forces on the sail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. If a sailing vessel should need to voyage without cargo then ballast of...
location.
Any two sailboats will have the same CSF value if their displacement and beam are the same. As an example, one could have a light hull with 50% ballast
Sailing ballast
Ballast is used in sailboats to provide moment to resist the lateral forces on the sail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. If a sailing vessel should need to voyage without cargo then ballast of...
in a bulb at the bottom of an eight foot fin keel
Keel
In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...
, the other could have a heavy hull
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
with 20% ballast in a 2 foot (0.6096 m) full-length keel
Keel
In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...
. The stability characteristics of the two sailboats will be drastically different despite the identical CSF value.