Praia Grande is the most accessible beach close to the centre of Angra dos Reis, reachable by local bus along the coast road. It is a long urban beach with calm water, backed by a strip of snack bars and kiosks. On weekends it fills with families from the town; on weekdays it is calm enough.
This is the practical option if you need a beach without organising a boat trip — handy for an afternoon, though not a substitute for the island beaches further out.