To go to Boipeba Island from Salvador by car, go to the São Joaquim Maritime Terminal in Salvador and take the ferry to Bom Despacho on Itaparica Island. It costs R$ 50.60 for a normal car (64,.70 for a large car) from Monday to Friday and R$ 71.70 on weekends and holidays (91.40 for large cars). The crossing to Itaparica takes approximately 1h and it can get quite crowded, so you might want to book your spot in advance.