at praça xv, bus 354 stops underground, in a tunnel not far from the terminal hidroviário da praça xv & estação das barcas, the boat terminal.

there is a boat that leaves praça xv every 30 minutes and reaches praia de charitas in 15 minutes.  

from charitas, the bus line 33 goes along the shore stops at praia da várzea / salinas, praia do cáis, and praia de jurujuba (final stop).