If you are coming from Florianópolis, must take a bus to Curitiba at the Catarinense office (departing each 2 h, average) at the main bus station, downtown, and exit at Itapema city bus station (+/- 70 km from Florianópolis) and take the Praiana bus to Bombinhas (better exit at the bombinhas beach bus stop - ask the driver). The last bus usually get out about 10 pm. If you are coming from Curitiba, do the same, inverse sense to Florianópolis.
There are regular daily bus lines between the state capitals Curitiba and Florianopolis and Camboriu.. There you will need to take a local bus - Praiana Line - to Bombinhas.
The best and easiest way is to drive to Bombinhas. Coming from Curitiba or Florianopolis, you will take the road BR-101 and take the exit on the km 243 to Porlo Belo/Bombinhas. After 10-15km you are already able to view the beaches.