Hull-form Definition and Hydrodynamic Calculations

As with any 2-D seakeeping program, firstly, the hydrodynamic coefficients need to be determined from the hull offsets. However, unlike many other packages, Hydro allows you to automatically generate the hull offsets at any stations by making simple planar cuts through the mainhull compartment. Up to 50 sections may be generated (which is ample).

With the hull offsets then being cut at the local draught, the underwater section is automatically generated. So, you simply have to decide at which stations these 2D cuts are to be produced, and again, defaults are provided.

Hydro can analyze the hullform by using one of two theoretical methods - either Lewis Sections, or the Frank Close Fit method, References 36. All further calculations will be based on these hydrodynamic calculations.

All information required above can be entered on a single tab sheet (see Seakeeping Dialog - Hydrodynamics Tab).

Having generated the hull offsets at a selected a loading condition (or using the default loading condition), it is possible to view the hullform graphically. The following information may be displayed for each 2D section

• Hull offsets

• Lewis interpretation of the section.

• The Frank Close points

Example of a Hullform Output

You can also plot a graph showing how valid the current hullform is within the constraints that Lewis applies. This graph plots B/2T vs. S/BT for each section, with the valid Lewis area bound by two lines. Any sections outside these lines can be seen by viewing the key at the side of the graph. The following image shows a typical Lewis validation graph.

You should use this diagram to determine which of the two available methods of calculating the Hydrodynamic Coefficients is most appropriate to their vessel.

Also, for each section the added mass and damping coefficients are tabulated.