A Coxswain qualification will qualify you to skipper a vessel up to 12 metres in length up to 15 miles offshore. Depending on your seatime you may be restricted to sheltered waters.

You require approx 1800 hrs or 12 months seatime to be eligible for a Coxswain's Certificate of Competency. This time may be reduced if you completed a ROPES book or all tasks in your Record of Service book.
The Coxswains certificate builds on topics learnt in the General purpose Hand.
If you have recently completed a GPH then you will gain recognition for the common units. In Coxswain's you will learn; basic navigation, engineering,  legislation, Collision Regulations, vessel handling, basic stability, radio communication, refueling, environmental considerations.

Coxswains typically work driving water taxis, skippering yachts, work boats, diving vessels Fisheries vessels. Many people that volunteer for rescue associations also hold a Coxswain's Certificate.  Some Coxswains continue to work as deckhands on larger vessels and gain seatime towards a master five.
To enrol in the Coxswain course click HERE
To gain the Coxswain Certificate of Competency see additional information from NSW Maritime HERE 

Other requirements

Please note that there are other requirements from the State or Commonwealth Maritime Authority that you must satisfy in order for you to gain a GPH, Skipper, or Engineering qualification. These relate to seatime, age, medical, eyesight and hearing. Before commencing a maritime career it is a good idea to check that you will be able to meet these requirements. Check with the Maritime Authority in charge of certification in your State or with AMSA for Commonwealth qualifications. See NSW Maritime requirements
Colour blindness
You can check colour vision here and also here