Jeff, you may need to consider clearance for the Brooklyn Marina (link above). It is located between the road bridge and rail bridge, so you need to go under the rail bridge. From Bluechart:
"HAWKESBURY RAILWAY BRIDGE
The two largest spans have a horizontal clearance of 128m; the nearest to the South Bank is recommended for navigation. The four centre spans have a horizontal clearance of 98m and the maximum vertical clearance overall is 11.4m."
Another one nearby is Hawkesbury River marina - right at the train station, and on the bluewater side of both bridges. I note they have showers, and very convenient to transport, but trains are noisy.
http://www.bia.org.au/member/HR-Marina/
However, you may find the areas around Avalon, Newport and Bayview more appealing. A search for marinas on Yellow Pages turns up quite a few. Sorry I am not familiar with their services and facilities.