This site is a small puzzle on the sand off Salmon Bay. It was found by a member of the public and inspected by the WA Museum in 2002. The remains consist of a boiler, a propeller and shaft, and two other unidentified pieces of iron, with very little other wreckage. The Museum's working theory, reported by divingwawrecks, is that the machinery may have been a surplus power plant due to be dumped at sea in the ships' graveyard further west, but that it was jettisoned or scuttled short of its destination.

At 26 m, it is one of the deepest wreck-related dives at Rottnest outside the graveyard. There is not much to explore, so the dive is short, but the machinery stands out on the seabed and attracts fish, and visibility on the south side of the island is often very good. Expect buffalo bream, western king wrasse, bullseyes around the boiler, and possibly larger fish such as samson fish or dhufish moving through.

It suits Advanced divers with their own boat who enjoy mysteries and want a deeper dive on the south coast, perhaps combined with a shallower reef such as Jack's Patch or Parker Point on the second tank. Treat it as a heritage site even though its identity is unknown. Plan the dive on nitrox to extend the short no-decompression time, and carry a DSMB because the shot can drift in current. A torch helps pick out the stamped fittings and details on the boiler that might one day help identify it.

Charter boats from Fremantle (Perth Scuba's Blue Destiny, Bucket List Diver, Dolphin Scuba) run across Gage Roads and round the east end of Rottnest to the south coast in roughly 50-70 minutes. Private boats launch at Fremantle Fishing Boat Harbour, Woodman Point or Hillarys; run along the south coast to off Salmon Bay (about 22-24 km from Fremantle) and locate the site by GPS and sounder. Drop a shot line; no moorings.

Open to southerly and south-westerly swell; divingwawrecks gives a limit of under 1.5 m. Best on calm summer mornings with north-easterly or easterly winds before the sea breeze. Visibility on the south side is often 10-25 m.

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.

Descend the shot to the boiler at 26 m, examine the shaft and propeller and the two unidentified pieces, then ascend the shot with a safety stop; bottom time is limited by no-deco limits on air, so nitrox helps. 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.

No regular operator - private boats and dive clubs. 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.