After you buy a foot passenger ticket to Cortes at the Campbell River ferry booth, walk to lane 7 where the Cortes line is and try to find a ride.
Connecting ferries from CR to Cortes are: 8:30, 10:30, 12:30, 2:30, 4:30 and the 6:15

On Tuesday the 10:30 and connecting 11:05 is a dangerous cargo sailing; no passengers.