PIAS contains two distinct hull form definition modules. The first and most prominent one is Fairway, for hull surface design and production fairing. That module is discussed in a dedicated page. Another module is Hulldef, with which a user can define an existing hull shape, i.e. a hullform originating from another source. To this end, Hulldef has three facilities:

• Typing over frame or ordinate coordinate tables.
• Digitizing frames, either by a digitizing tablet, or from a picture on screen.
• Importing frame positions and shapes from a number of file formats.

The basic modelling entity of Hulldef is a transverse cross section — a frame, or ordinate. For each cross section an arbitrary number of breadth-height coordinates is defined. Hulldef constructs a curve through these points, except on points of a chine, which are explicitly marked as such, where the frame shape has a knuckle point. Although this definition is simple – actually it constituted a wireframe model, not a surface — this is sufficient for all of PIAS’ computations. With the advantage of a blazingly short amount of man hours for the definition work (depending on the number of sections typically some ½ to 4 hours).

Although the main purpose of Hulldef is the definition of this wireframe hull model, some additional features are available:

• Generation of parametric cylindrical shapes, also with standardized tank end shapes as custom for cargo gas tanks.
• Defining deck line, as well as different types of openings.
• Defining windage area (wind contour) and wind pressures.
• Export the defined hull shapes and particulars to a printed report and to clear sketches. This Hulldef output can for example serve in a stability booklet.