The Zanoni is one of the most complete sailing-ship wrecks in Australian waters and among the most important historic dives in South Australia. She was a 338-ton composite barque, 139 feet (42 m) long, built at Liverpool in 1865 by W.H. Potter & Co for Thomas Royden & Son and intended for the East India trade.

On 11 February 1867, loaded with bark and 4,025 bags of wheat and bound for Port Adelaide, she was struck by a sudden, violent, short-lived squall while crossing Gulf St Vincent and capsized and sank within minutes. Remarkably, all sixteen people on board – the master, Captain Summers, 13 crew and two stevedores – were rescued. The wreck lay forgotten until it was located by divers in the early 1980s, and it was declared a historic shipwreck on 12 May 1983 with a 550 m radius Protected Zone.

Because she sank quickly in open water onto a soft seabed rather than breaking up on a reef, the hull is remarkably intact. She lies on her side in about 18 m, and divers can trace her lines from the bowsprit to the stern, with masts, sternpost, rudder and parts of the superstructure still in place. Composite construction – iron frames with timber planking – makes the Zanoni a rare surviving example of a transitional shipbuilding technique.

The surrounding seabed is barren sand and silt, so the wreck acts as an oasis. Sponges colonise the hull, and snapper, leatherjackets, old wives, yellowtail and bullseyes congregate around it, with blue swimmer crabs on the sand. Diving the Zanoni is a privilege rather than a routine outing.

Every visit requires a permit, and to reduce pressure on the wreck an alternative site – the Ardrossan Barge – was scuttled nearby in 1984 for fishing and general diving. Divers visiting the Zanoni should be comfortable in open water at 18 m, have good buoyancy to avoid contact with fragile timbers, and treat the site as a museum.

The wreck lies in open water about 10 nautical miles (18-19 km) south-east of Ardrossan and 5 miles west-north-west of the Long Spit buoy. Private boats launch at Ardrossan (about 40-50 minutes in calm conditions); from Adelaide, charter and private boats run from North Haven/Outer Harbor, roughly an hour across the gulf. A permit from the Department for Environment and Water (Heritage South Australia) is required before any vessel enters the 550 m Protected Zone or anyone dives; permit holders are given the mooring position and conditions.

Anchoring on the wreck is prohibited – use the mooring.

Mid-gulf, the Zanoni is exposed to wind from every direction and there is nothing to hide behind, so it is only dived on flat days – winds under about 10-12 knots and no significant wind-chop. South-westerly and southerly fronts raise a short, steep sea in the gulf quickly, and afternoon south-easterly sea breezes in summer can make the return crossing rough, so morning dives are preferred. Tidal current is usually mild but can run on big spring tides; aim for neap tides or the turn.

Visibility depends on recent weather: after several calm days it can exceed 15 m, but a blow stirs the fine seabed and it may take days to clear.

Descend the mooring to the hull, orient on the exposed side of the ship, and swim a slow circuit around the wreck at 16-18 m – bow and bowsprit, along the deck line past the fallen masts, stern post and rudder – without touching. Return to the mooring line and ascend with a safety stop at 5 m. Penetration is not permitted.

Recreational depth (18 m) but no natural reference other than the mooring; carry an SMB. Fragile composite timbers – no penetration, gloves discouraged to avoid touching.

No regular commercial trips; dived by permit-holding clubs and private groups (SDFSA-affiliated clubs, Adelaide shops organising permit dives from North Haven or Ardrossan) a few times a year.