Recently, it was shown how to make a multipurpose broadband HF antenna system out of existing naval superstructures such as the funnel or a big mast. The idea was discussed by means of canonical structures, e.g., a cylindrical body of circular or square cross-section, placed onto an infinite ground plane. This paper investigates the critical aspects concerning the extension of naval structural antenna concept to real ship platforms with the aim to define a general design methodology for impedance matching and radiation pattern control. The method is described,with reference to a realistic, frigate model, whose big mast is transformed into a broadband HF antenna system able to perform communications by both sea-wave and sky-wave links. It is demonstrated that, even in a real environment, the multiport strategy permits to increase the system efficiency and to moderately shape the radiation pattern in order to overcome the shadowing effect due to other large objects.