In the Edit | Preferences dialog of Hydromax, calculation tolerances can be set. This defines the tolerances that Hydromax uses to determine when to finish iteration during

§   Large Angle Stability

§   Equilibrium analysis

§   Specified conditions

§   KN calculations

§   Floodable Length

§   Longitudinal Strength

Ideal tolerances can range between 0.00001% and 0.1%  (1 gram in 10 tonnes of displacement). Acceptable tolerances can range from 0.001% to 1.0%. Acceptable tolerances should always be greater than Ideal tolerances.

Hydromax will attempt to solve most analysis to within the ideal tolerance. If this is not achieved within a certain number of iterations, but the acceptable error has been achieved, Hydromax will continue. If convergence to within the acceptable error has not been achieved, Hydromax will display a warning.

One of the most common causes of non-convergence is if the specified displacement exceeds the volume of the completely submerged vessel and it sinks. Also convergence may be poor if the trim angle approaches ±90°. If Hydromax thinks that it is likely that the model has sunk (waterplane area is zero at the current condition) the following dialog will be displayed. The specified displacement and the actual displacement at the current iteration are provided for information.

Note

This warning is not displayed during batch analysis, instead the warning is written in the batch file.

If there is a convergence problem, which appears not to be due to sinking, then the following dialog will be displayed.

This problem can sometimes occur if the specified displacement is extremely small and the vessel has a large flat bottom, producing a highly non-linear waterplane area vs. draft plot. Other causes of non-convergence can be non-linear moment to trim vs. trim angle curve or moment to heel vs. heel angle curve.

Note:

There are occasions when convergence will not necessarily occur within the maximum allowable number of iterations. If Hydromax fails to converge it will give you a warning, but will allow you the option of continuing the search. If you choose to continue, Hydromax will search for the equilibrium position indefinitely. If the search is unsuccessful after a reasonable period of time, you can interrupt Hydromax by pausing the analysis.

The analysis will also fail to converge if the trim becomes excessive. All analyses other than Floodable Length will fail if the trim exceeds +/-45º; in the case of the Floodable Length analysis, this limit is increased to +/-89º.