Chinamans Hat is a small, distinctively shaped islet off the Innes coast west of Stenhouse Bay, and it offers one of the more interesting reef dives in the park for divers with boat access. A visible reef encircles the island, and both The Dive Shack and visitor information describe numerous swim-throughs, chimneys, caves, ledges and crevices down to about 15 m. The limestone reef has been eroded by the Southern Ocean into a maze of gutters and holes.

Kelp and brown algae cover the tops, while the walls and cave roofs carry sponges, ascidians and the occasional gorgonian. Fish life is abundant: sweep, old wives, magpie perch, zebrafish, western blue groper, harlequin fish and schools of trevally, with blue devils in the holes and occasional crayfish. The Dive Shack also mentions dolphins visiting.

Shore access is possible but hard work. The Marine Life Society describes a long walk from the car park to the beach followed by a taxing snorkel to the reef, which makes it a site for the fit and determined on flat days. By boat from Marion Bay it becomes a straightforward and very enjoyable dive.

Being open to the south-west, it is swell-dependent and best on northerly days. The combination of structure and fish makes Chinamans Hat a good choice for divers who have done the Stenhouse Bay jetty and want to explore the wilder reef of Innes without committing to the long run out to Althorpe Island. A torch is useful in the caves, and on a good day the island's lee side also makes a pleasant snorkel for the boat crew between dives.

From Adelaide drive about 300 km (3.5 hours) via Port Wakefield, Minlaton and Warooka to Marion Bay; Dhilba Guuranda-Innes National Park begins just west of the township (vehicle entry fee, pay online or at the Stenhouse Bay visitor centre). By boat, launch at Marion Bay and run west past Stenhouse Bay to the island (15-20 minutes). By land, follow the park road to the Chinamans Hat/ West Cape area turn-off, walk the track from the car park down to the beach and snorkel out to the reef – the Marine Life Society describes this as a long walk followed by a taxing snorkel, so it is only for fit divers in flat conditions.

The southern tip of Yorke Peninsula faces the open Southern Ocean and Investigator Strait, so south-westerly and southerly swell is the controlling factor: most exposed sites need swell under about 1.5 m and are best after several days of northerly or north-easterly winds, which blow offshore along this coast. Winter cold fronts bring big south-westerly swell and strong winds and can close the area for days. Summer afternoon south-easterly sea breezes make boat runs rough, so launch early.

Visibility is typically 10-20 m in settled conditions but drops sharply with swell-driven surge. The Marine Life Society advises Chinamans Hat is best during a northerly wind with low swell.

Anchor on the sheltered side, descend to the reef at 8-10 m and circle the island, exploring the swim-throughs, chimneys and caves on the seaward side at 12-15 m, then shallow up along the reef for the safety stop.

No resident operator; visited by Adelaide shop and club trips with boats and private boats from Marion Bay. Visitor information recommends it for experienced divers only.