This action, available from [Solids]→[Increase/Decrease Parallel Section] or the keys <Alt><O><P>, allows to quickly change the length of the parallel mid-section of a solid. It works by moving all points forward of the given [Aft position of parallel section] to satisfy the given [Length between perpendiculars]. This transformation is also available from the Fairway main menu, see Increase/decrease parallel midbody.

Lengthening a hull by adding a parallel section.

Attention: Because this transformation shifts frames to new positions, you may want to apply [Systemize polycurve names] to update the names of frames according to their new position.