+1 for Pinta, and for Refuge Bay - pretty much take your pick - yes, they are mostly private/club moorings, but at this time of year its mostly empty- particularly mid-week (flying any club pennant will fool many

). I like to go deep up into America Bay near to the waterfall. Moorings to starboard will get the morning sun earlier.
If you go here:
www.nsw.gov.au/driving-boating-and-transport/using-waterways-boating-and-transport-information/navigation-and-communication/boating-maps?utm_source=seabreeze.com.au#toc-hawkesbury-riverbroken-bay-mapsand download the '
9a-cowan-narrabeen' map(PDF, so you can keep it offline), you'll see all the public moorings in the whole system. Have a look at Smiths Creek if you can - very nice