Port Douglas is a small touristy town in the north of Cairns. The town is popular among working holiday makers, because there are many resort where you might want to look for a job.
The local Yachting Club organizes each Wednesday free sail tours. If you would like to participate go there and talk to the people to have a chance that they take you out there. In our experience it is easier for “normal” travelers and not backpacker, but definitely worth a try. Street View image shows the parking area right before the Yachting Club – maybe you can also consider it to camp there for free.
Port Douglas QLD, Australia-16.483611145.465278