Product(s):	MAXSURF Stability
Version(s):	23.06.00.137
Area:	Limiting KG

Problem

When running a Limiting KG calculation I get a message for one data point "Convergence error". 

Solution

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.

• If they pass - increase the VCG
• If they do not pass - lower VCG

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: 

• Increase acceptable analysis convergence tolerance: Edit | Preferences menu
• Run fixed trim: Analysis | Trim

See Also

Crash Occurs During Analysis