The Thornliebank is the shallowest identified wreck in the Rottnest ships' graveyard and therefore the most accessible to technical divers. According to WreckSploration she was a 1,492-ton, three-masted iron barque built in Glasgow in 1886 by Joseph Russell for Andrew Weir and Co., measuring 244.5 by 37.6 feet, and was sold to Australian owners soon after launching. On 6 August 1891 she caught fire at anchor in Cockburn Sound; after two days of firefighting her twisted beams and plates made repair uneconomic, and she became a coal hulk in Fremantle harbour. A second fire on 18 April 1928 ended her working life, and the 42-year-old hull was towed out and scuttled off Rottnest. The WA Museum graveyard précis lists her scuttling in 1928.

WreckSploration and the Maritime Discovery Group located the wreck (Graveyard Site 44) on 13 October 2024 and modelled it in November 2024. She lies in about 46 m, oriented north-south with the bow to the south. The hull is about 69 m long with a counter stern and straight stem, and two masts - the main and mizzen - still stand, matching photographs taken at her scuttling. Collapsed plating and structure amidships may be remains of coal-handling gear or boiler bases.

This is a serious open-ocean decompression dive on a rarely seen nineteenth-century sailing-ship hull, suitable only for trained technical divers with their own support. Divers visiting should record and share observations with the research teams rather than disturb anything on the hull, and should expect to fund and run the whole operation themselves.

The graveyard lies well offshore to the south-west and west of Rottnest, roughly 30-40 km from Fremantle. There are no moorings or public marks; teams run from Fremantle or Woodman Point in capable private or club boats (UWA Underwater Club, WreckSploration) with accurate GPS positions and sounders, drop a shot line onto the wreck and dive with surface support. Allow 1-1.5 hours each way.

This is not a commercial charter destination.

Fully exposed open-ocean site; needs low swell and light winds, normally summer or autumn mornings before the sea breeze. Currents on the surface and at depth vary; plan for a drifting decompression. General pattern at Rottnest: summer brings calm morning easterlies followed by a strong south-westerly sea breeze from late morning, so dive early; winter brings north-westerly fronts and large swell, with clear, calm spells between them.

Check the Bureau of Meteorology coastal forecast for swell height and period before committing.

Shot the hull, descend to the deck at about 40-44 m, tour from the counter stern forward past the standing main and mizzen masts towards the bow (south), then ascend the shot for staged decompression. Agree a turn pressure before descending (half gas, or a third where current is likely), carry a DSMB, and make a 3-minute safety stop at 5 m.

Nitrox/trimix bottom gas and deco gases recommended (46 m); rebreathers suited; drift deco under DSMB with chase boat. Positions from WreckSploration.

No commercial operator; located and surveyed by WreckSploration and the Maritime Discovery Group (October-November 2024); private technical teams only. Nearest dive services: Perth Scuba, Bucket List Diver and Dolphin Scuba (Perth/Fremantle) run Rottnest boat trips; there are no dive shops or air fills on the island.