The margin line is used in a number of the criteria. Hydromax automatically calculates the position of the margin line 76mm below the deck edge when the hull is first read in. If necessary, the points on the margin line may be edited manually in the Margin Line Points window (the deck edge is automatically updated so that it is kept 76mm above the margin line).

It is only necessary to modify the height value of the margin line points. Once this has been done for all the points that need to be changed, selecting Snap Margin Line to Hull in the Analysis menu will project all of the points horizontally onto the hull surface, ensuring that the margin line follows the hull shape precisely. Asymmetric margin lines and deck edges are not supported.

Points may be added or deleted as required using the procedure described in Adding Key Points and Deleting Key Points on page 61.