Chinaman's Hat is an octagonal structure serving as a shipping channel marker and haul-out for local brown fur seals, in the South Channel of Port Phillip in the Australian state of Victoria. It is in the Mornington Peninsula Shire, 3 km (1.9 mi) east-south-east of Pope's Eye. Along with the latter it served as a navigation beacon at the Heads of the bay.
The term Chinaman's Hat is the local name once associated with the site of a former military structure, Station M, but now transferred to a new seal platform erected by Victoria's Park Authority in 2002.
The postwar structure was built to replace a dilapidated military installation erected on a dolphin as part of the Port Phillip bay defence system shortly before 1942. This earlier structure is often said to have supported an optical mount, or 'magic eye which transmitted two piezo electronic beams across the Rip to a large mirror, and then to two reflectors, respectively Station P, and Station S, at the heads of Point Lonsdale. Any break in transmission in such a system was designed to set off an alarm to signal the possible presence of enemy vessels. The mechanism apparently did not function as expected, and the equipment was removed two years later, in 1944. Some doubts, however, have been expressed regarding the existence of this interception system: the site certainly was equipped in wartime with underwater indicator loops to detect submarines.
After it was abandoned, the dilapidated remains were used as a perch for both recreational fishing and as an anchorage. It rested on a circular concrete caisson base, roughly 7 m (23 ft) in diameter, raised on a sandy shoal some 6 m (20 ft) below the waterline.Parks Victoria was granted a permit in early 2002 to demolish the old structure after arguing that it posed a risk for small craft navigation and was devoid of heritage value. In the face of public protests, the Authority went ahead and built, at a cost of A$210,000, an expensive alternative platform which was quickly disparaged by critics at the time as a veritable "Taj Mahal for seals". This new structure for the seal colony was grounded on a rectangular base and lies not far from the Mud Islands bird sanctuary. However, the seals refused to budge from their traditional, run-down landmark, and it was only after the authorities proceeded to demolish the old haul-out that they settled on the new platform. It is this new structure which now carries the name Chinaman's Hat.The present structure is one of four haul outs or resting sites in the bay, and is occupied by a bachelor community of the Australian fur seals. It is a popular destination for scuba divers and snorkelers. Visitors to the site are warned to keep their distance, since the seals can at times behave aggressively towards people who approach too close.