Chinamans Hat is the seal stop of Port Phillip. The name belonged to a Second World War defence structure, Station M, an octagonal concrete platform on piles beside the South Channel that after the war became a haul-out for Australian fur seals. By 2002 the old structure was collapsing and Parks Victoria demolished it as a navigation hazard, replacing it with a purpose-built seal platform that critics at the time called a 'Taj Maul for seals'. The seals moved straight in, and the new Chinamans Hat is now the most-visited wildlife site in the bay.

Australian fur seals are the largest fur seal in Australian waters; the bulls can exceed 300 kg. They haul out here between fishing trips – the Scuba Doctor listing notes that 'the seals need to haul out of the water and have a deep sleep every few weeks after days of fishing' – and, unusually among seals, they are sociable, sparring and lying over each other on the platform and swimming in loose groups around it. In the water the younger animals are curious and will come within arm's length of a snorkeller who stays still; the rules, which are enforced, are that swimmers keep 5 m from seals and vessels 30 m from the haul-out, with no touching or feeding. Cormorants roost on the structure and dolphins pass through the channel.

Underwater the site is plain: sand and shell at 2–12 m around concrete piles that have grown a coat of mussels, sponges and kelp, with leatherjackets, wrasse and rays around the bases. It is not dived for the reef. It is snorkelled, mostly from the licensed dolphin- and seal-swim boats out of Sorrento and Queenscliff, and included as a surface-interval stop by dive charters returning from the Heads. For a diver visiting the Heads it is the easiest close encounter with fur seals in Victoria, and it is one of the few Heads sites suitable for children and non-divers.

Boat access only, 10–12 minutes from Portsea Pier or Sorrento, 20 from Queenscliff. The platform is a navigation structure beside the South Channel and landing is prohibited; vessels must stay 30 m or more from the haul-out and swimmers 5 m from the seals, with licensed tour operators permitted closer under their conditions. Private boats from Sorrento ramp can visit but must keep clear of the channel and the dolphin-swim vessels.

Tide reference: WillyWeather 'South Channel Pile Light'.

No slack-water restriction is published and the site is snorkelled on most tides, but the South Channel current runs hard past the piles on springs and swimmers should enter up-current of the structure and keep the boat close. Sheltered from southerlies and westerlies by the Nepean peninsula; a strong northerly makes it choppy and reduces visibility, which is 5–12 m on the sand. Year-round; seals are present in numbers in all seasons, with most in autumn and winter after the breeding season; water 12–19 °C so a 5–7 mm suit is needed even for snorkelling.

Snorkel or scuba from the boat 20–30 m up-current of the platform, hold position off the piles at 2–6 m and let the seals come to you; do not approach within 5 m or swim under the platform. Scuba divers can drop to the sand at 10–12 m around the pile bases for rays and small fish, then ascend in the lee of the structure for pick-up.

Primarily a snorkel site: Moonraker Dolphin Swims (Sorrento), Polperro Dolphin Swims (Sorrento), Sea All Dolphin Swims (Queenscliff) and Bayplay (Portsea) visit daily in season; Dive Victoria Group and Bayplay include it as a snorkel stop on dive charters; scuba here is occasional.