The SS Coramba is a 1907 steamer that sank in a 1934 storm and now lies in 66 m of Bass Strait water off the south coast of Phillip Island — a deep wreck with serious history. She sits intact and upright with the structure encrusted in 90 years of sponge growth, gorgonians and ascidians, surrounded by big bullseye schools, blue devils, banjo sharks and pelagic fish moving through. At 66 m she's strictly a technical dive — mixed-gas, full deco, twin sets, real tech training. Boat-only access via charter operators running tech trips out of the bay. Conditions need to be properly settled: light north-east winds, swell under 1 m, tide near slack so the run out and shot line stay calm. Use the live 7-day forecast on this page to plan. Technical divers only — 66 m, full deco, gas planning, no recreational version of this dive.
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.