Chikubushima can be reached from Nagahama Port, Hikone Port, or Imazu Port (Takashima). I always use Nagahama Port (photo) to visit Chikubushima. Nagahama boat schedule
Boat cruise company Biwako Kisen (琵琶湖汽船) operates round trip boats from Nagahama daily. Schedule varies depending on the season (fewer boats in winter). No reservations necessary.