If the weather is good, a chart plotter will make it easier but there are channel markers the whole way. No issues if you have the right day but even if low wind watch the swell when you get outside. And take plenty of fuel. Probably look for any day where it's not forecast for 15knots or more. A howling south Easter in the arvo might be the biggest risk.

 Yeah pretty easy. A cranking easterly heading home is the thing that would deter me as I've done it before and it took us nearly 3 hours to get back to shark bay from shelter bay in a 6.7mtr boat. Your normal easterly morning and then seabreeze arvo would be ok to go. 

 Across the main channel from the outer Denham marker to the channel across the prongs, the sea will really kick up if it is running tide opposite to wind, ie, southerly and a run-in tide. or even a fresh s'easter. Tide running out, not much problem as the tide and wind are running the same direction. Across the shallow flats either side of the main channel, no problems. Maybe a bit of the same issue heading down to the channel thruogh the flats as you get towards South Passage.

I took a 50ft semi-displacement boat back into Denham once after we had been right up the prongs sheltering from a strong SSE up against Cloughs newest causeway. We made a break for it one morning when we though it had abated a bit--this is the first private boat single engined to ever do an east-west crossing of the great Australian Bight, so it was no slouch in a sea. After stuff started breaking loose and crashing down in the galley from the steep beam sea whipped up, I had to lay the course off the the s/east to quarter into it, until the sea calmed as I neared the other side, and I turned and headed up to the Denham leads with a following sea. This was tide running in, wind from the south, less than 20 kots.

 Wow.. Thanks guys. I'm heading back up there in late March 17 for two weeks. I'll take your advice and look for the more favourable <15 kn winds. I followed all the markers to the ocean, but didn't see any markers at the final entrance to the open sea. That's the bit I wasn't game to cross. Thanks for replying. 

 Closer to the left on your way out, you will see a long surf break coming out on your starboard side running out from the southern end of DHI.

good amount of safe deep water to go through, not a bar to cross or anything mate