Pengaruh karakteristik, pengetahuan dan sikap terhadap persepsi berisiko tertular Infeksi Menular Seksual (IMS) pada pelaut di Pelabuhan Penyeberangan Merak-Bakauheni 2012 = The effect of characteristic knowledge and attitude towards risk perception of infected Sexually Transmitted Infections (STIS) within seaman in the harbor of Merak-Bakauheni 2012