Port Phillip Heads — the Rip — is the narrow ocean entrance between Point Nepean and Point Lonsdale where Bass Strait pours into Port Phillip Bay. It's the most famous drift dive in Victoria, with depths around 14 m on the reef shelves and stronger water dropping deeper into the channel. Marine life is thick: crayfish, blue devils, weedy seadragons, big snapper and pelagic schools rolling through on the tide. You only dive the Rip on slack water — roughly 30 minutes either side of high or low — and only with skippers who know the timing. Conditions are best in light north-quadrant winds with swell under a metre. South or south-west swell shuts it down fast. This page gives you the live 7-day wind, swell and tide forecast, with NOW marked so you can plan your slack water window. Advanced divers only — current and boat traffic make it serious water.
How far you can see underwater — measured in metres. 10m+ is great, 5–10m is workable, under 3m is murk. Driven by wind, swell, and recent rain.
Long-period waves rolling in from the open ocean. Direction matters more than height — a S swell hits Portsea hard, but an E swell rolls past. Period over 12 s = real ocean punch.
Offshore (N or NE) flattens the surface and clears the water. Onshore (SE through SW) chops it up and stirs sand. Calm or light offshore is the magic combo.
This site faces the open ocean. The exposure caption above shows which directions slam in. Anything from the opposite side gets blocked — that's the safest window.
Slack water — the 30 minutes either side of high or low — is calmest and clearest. Mid-tide brings the most flow. Plan to be down at slack, up before the run picks up.
Bass Strait sits 14–16 °C autumn–winter, 17–19 °C summer. Below 16° a 7 mm hooded keeps you warm for 60 min+. Drysuit if you're going long.