STIX
What is STIX?
STIX is the acronym for STability IndeX. STIX is a way of expressing a boat's dynamic stability with a single value.
The higher the STIX value, the more stable the boat when under way.
Monohull sailing yachts between 6 and 24 meters manufactured in EU since 19xx must have STIX value and all manufacturers have had to offer STIX information.
How to calculate STIX?
Calculating STIX values is slightly more complex than calculating the AVS.
STIX = (7 + 2.25LBS) x F0.5
where F = FDS x FIR x FKR x FDL x FBD x FWM x FDF
and LBS = (2 x LWL + LH)/3
The base value is calculated using the length LBS, where the longer the boat the higher the base value will be. This base value is then multiplied with 7 factors, each having an impact on the stability of the boat. A factor will increase the boats overall dynamic stability.
Dynamic stability factor (FDS)
This factor represents the inherent righting energy (relative to its length) to be overcome before a stability incident occurs.
FDS shall never be taken as less than 0.5 or greater than 1.5.
Inversion recovery factor (FIR)
This factor represents the ability to recover unaided after an inversion.
FIR shall never be taken as less than 0.4 or greater than 1.5.
Knockdown recovery factor (FKR)
This factor represents the ability of a boat to spill water out of the sails and hence recover after being knocked down.
FKR shall never be taken as less than 0,5 or greater than 1,5.
Displacement-length factor (FDL)
This factor accounts for the favourable effect of heavier displacement on a given length increasing the resistance to capsize.
FDL shall never be taken as less than 0,75 or greater than 1,25.
Beam-displacement factor (FBD)
This factor accounts for the increased vulnerability to capsize in beam seas of boats with appreciable topside flare, and increased beam in relation to displacement.
FBD shall never be taken as less than 0,75 or greater than 1,25.
Wind moment factor (FWM)
For boats where either φD or φDH is less than 90°, this factor represents the risk of downflooding due to a gust of wind heeling an unreefed boat.
FWM shall never be taken as less than 0,5 or greater than 1,0.
Downflooding factor (FDF)
This factor represents the risk of downflooding in a knockdown.
FDF shall never be taken as less than 0,5 or more than 1,25.
STIX = (7 + 2.25LBS) x F0.5
where F = FDS x FIR x FKR x FDL x FBD x FWM x FDF
and LBS = (2 x LWL + LH)/3
The base value is calculated using the length LBS, where the longer the boat the higher the base value will be. This base value is then multiplied with 7 factors, each having an impact on the stability of the boat. A factor will increase the boats overall dynamic stability.
Dynamic stability factor (FDS)
This factor represents the inherent righting energy (relative to its length) to be overcome before a stability incident occurs.
FDS shall never be taken as less than 0.5 or greater than 1.5.
Inversion recovery factor (FIR)
This factor represents the ability to recover unaided after an inversion.
FIR shall never be taken as less than 0.4 or greater than 1.5.
Knockdown recovery factor (FKR)
This factor represents the ability of a boat to spill water out of the sails and hence recover after being knocked down.
FKR shall never be taken as less than 0,5 or greater than 1,5.
Displacement-length factor (FDL)
This factor accounts for the favourable effect of heavier displacement on a given length increasing the resistance to capsize.
FDL shall never be taken as less than 0,75 or greater than 1,25.
Beam-displacement factor (FBD)
This factor accounts for the increased vulnerability to capsize in beam seas of boats with appreciable topside flare, and increased beam in relation to displacement.
FBD shall never be taken as less than 0,75 or greater than 1,25.
Wind moment factor (FWM)
For boats where either φD or φDH is less than 90°, this factor represents the risk of downflooding due to a gust of wind heeling an unreefed boat.
FWM shall never be taken as less than 0,5 or greater than 1,0.
Downflooding factor (FDF)
This factor represents the risk of downflooding in a knockdown.
FDF shall never be taken as less than 0,5 or more than 1,25.