Chromosomes (solutions) are rated by the fitness function to determine which solutions should survive to the next generation. The fitness function uses three different criteria to rate the solutions. The default settings include all three criteria. Uncheck a criteria if you do not want to include it in the optimization. Keep in mind that at least one criteria has to be selected.
Stability
If this criteria is checked, solutions with a low free surface effect will be rated high. Solutions will mainly have full and empty tanks.
Trim
The desired trim will be taken into account is this criteria is checked.
Hull stresses
This criteria tries to find the optimal balance between the buoyancy forces and the weight of the ship.