it takes between 10 and 20 minutes to cross the bay, and the fare varies depending on the boat and the route.  

the ferry to charitas is the boat that arrives closest to the area in niterói where there are the most hills - and on this link is the schedule from praça xv.

going by car  is fairly complicated,  and navigating through niterói's streets can be quite difficult, even with a gps.

the car ride includes crossing the longest bridge in brazil, the ponte rio - niterói which just like the name implies, connects the two cities.