Hardys Bay (Brisbane waters0

The sand bar at the entrance to Brisbane Water and the end of Ocean Beach is known as ''The Box'' by surfers and indeed it is not a place you want to be in a yacht in a heavy southerly swell. In those conditions the Ettalong to Palm Beach ferry stops running.
But if the swell is from the east or north east, there won't be any surf. However, don't stray out of the channel and keep to the side of the rocks ( starboard side going in ) and keep your depth sounder on.
Half Tide Rocks at the actual entrance of the harbour means you have to do a big dog leg and the tidal stream can be quite strong at this point so prepare to swept wide ways as you navigate this acute bend in the channel.
The remainder of the passage to Hardy's Bay is less stressful but don't take your eye off that depth sounder. There's plenty of water for your draft but you don't need to stray too far before there isn't. The channel is will marked but there are a lot of sand shoals in the first part of the channel that are constantly changing.
I definitely don't want to put you off but I would recommend that for your first trip, you choose a day that isn't too windy and on rising tide just in case you do go aground.
And forget it in a southerly swell unless it's only small.
It's a nice place and well worth a visit.

I'll also add to Stonny's info, that if possible try and time going around Half Tide Rocks for after the ferry goes around it.

We took our catamaran up there a while ago and were coming in with an incoming tide when the ferry appeared going out. You are beam on to some of the current when approaching the turn and there's not enough width for the ferry and my cat there. It's a bit unnerving pointing the bows towards the shallows to account for the tide pushing you into the ferry's path!

Luckily we just pulled up the centreboards and made a run for the shallows to get out of the way...