QUESTION:
When running a Limiting KG calculation I get a message for one data point "Convergence error".
ANSWER:
Limiting KG analysis calculates the maximum KG at which the selected criteria pass. Analysis process:
1. Calculate GZ curve for a specific Vertical Centre of Gravity (VCG) - see if criteria pass.
2. Continue iterating until the highest VCG (to within around 1mm) where all the criteria pass.
Assumption: The criteria are more likely to pass if the VCG is lowered, and more likely to fail if VCG is raised. This is not always the case. For example: angle of max GZ is relatively insensitive to VCG for many vessels; and angle of downflooding may not change or may change in the opposite way.
Convergence errors can occur when:
1. Unable to calculate GZ curve - e.g., displacement too large; or VCG so high that trim balance cannot be found (longitudinal stability more critical than transverse).
2. Unable to find a VCG where all criteria pass - e.g., downflooding point is immersed at zero heel.
3. Unable to evaluate criteria - e.g., GZ angle range not sufficient: roll-back angle for weather criterion.
To fix the error you can try: