The John Robb is the most remote of Adelaide's metro-listed wrecks, lying 12-15 km offshore near the outer shipping channel in 18-20 m. She was built at Port Adelaide in 1879 and sank during a storm around 1910. Today she is nearly completely broken up, and only the bow section, pointing west, remains clearly recognisable among a scatter of debris.

Every local source stresses how hard she is to find. There are no landmarks at this distance offshore, so an accurate GPS position is essential, and the Dive Shack calls the site extremely difficult to locate. Strong tidal currents are also noted, so the dive must be timed for slack water.

Visibility is typically better than inshore because of the distance from the coast, but the Marine Life Network notes it can be fair to poor and is quickly affected by careless finning. Marine life is variable. The Marine Life Network lists old wives, bullseyes, spider crabs, nudibranchs and cowfish, and notes juvenile fish in spring.

The wreckage offers the only hard structure on a wide area of sandy seabed, so it tends to hold fish on good days. The John Robb is a dive for experienced divers with their own well-equipped boat, a good GPS mark and a calm, settled day. It is less about spectacular scenery than about the satisfaction of finding and exploring a genuinely historic, rarely visited wreck far out in the gulf.

It is protected as an historic shipwreck: look, photograph and leave everything in place.

Boat access only. Launch at the North Haven boat ramp (Lady Gowrie Drive, North Haven; multi-lane ramp inside the marina, large trailer park, toilets), about 25 minutes north-west of the Adelaide CBD. Exit the marina and run about 15 km west into the gulf (30-40 minutes) to the GPS mark.

There are no public moorings. The wreck lies close to the Port Adelaide shipping approaches, so keep a lookout for large vessels, anchor clear of the channel and never leave the boat unattended – local shops stress that surface support is essential here.

These northern gulf sites are open to wind from most directions and need a calm day: easterlies are best, while westerlies, south-westerlies and the summer sea breeze (usually from late morning) build a steep chop. Tidal currents are the key issue – both the Dive Shack and the Marine Life Network describe strong tidal currents, so plan the dive for slack water, ideally on a neap 'dodge tide' when the water barely moves. Visibility is variable: it can be good on calm, clear days but is often fair to poor, especially after westerly blows, after rain (Torrens and Port River outflow) and when divers stir the bottom.

Watch for shipping movements in and out of Outer Harbor. Being well offshore, the John Robb needs a settled forecast for the whole day.

Use an accurate GPS mark and drop a shot on the bow section, which points west. Descend at slack water, explore the bow and the scattered debris nearby at 18-20 m, and ascend on the shot with the boat following.

Protected historic shipwreck: no disturbance or removal.

No regular charter – private boats and occasional club dives from North Haven only.