There are lots of ways to get to McKell St, Mort Bay Park, by public transport - so many in fact that it is impossible to do more than give you the general idea (refer to the google map in the Venue page) - so here goes:
BY FERRY - this is the scenic way to travel! The closest ferry wharf is Balmain (Thames St) about 250m from the venue or East Balmain wharf (about 1.2km) or Birchgrove (Louisa Rd - about 1.5km). All these are on the same route "Balmain and Woolich". Other stops include Greenwich, North Sydney and Circular Quay. See Sydney ferries website for timetable details which vary between Fridays and weekends: http://www.sydneyferries.info/timetables.htm
BY BUS - There are lots of buses but the 441 is recommended as the most direct if coming from the city and drops you about a 2 minute walk from McKell St - check the State transit website for timetables, maps and other details http://www.sydneybuses.info/timetable/ but here is a quick summary:
433 - City to Darling St Balmain via Central, Glebe & Lilyfield;alight Darling St near Church St (Bus stop No 204140)
434 - City to Balmain East Wharf via Central, Glebe & Lilyfield;alight Darling St near Church St (Bus stop No 204140)
432 - City to Birchgrove, Grove St, via Central, Glebe and Lilyfield; alight Rowntree St near Cameron St
441 - MOST DIRECT - City to Birchgrove, Grove St via Ultimo and Anzac Bridge; alight Rowntree St near Cameron St
442 - City to Balmain East Wharf via Ultimo and Anzac Bridge; alight Darling St near Church St (Bus stop No 204140)
445 - Canterbury Station, Broughton St to Balamin Easst Wharf via Lewisham, Leichhardt and Rozelle; alight Darling St near Church St (Bus stop no 204140)