The Empress of the Sea was one of the great American clippers. Built at Boston in 1853 by Donald McKay – builder of the Flying Cloud and the Lightning – she was a three-masted wooden ship of 2,200 tons and 73 m (240 ft), with a female figurehead and a mahogany saloon, and after a career on the American routes she joined James Baines' Black Ball Line carrying emigrants and cargo between Liverpool and Melbourne. On 19 December 1861 she left Hobsons Bay with 12 passengers, 45 crew, cargo and £80,000 in gold. Off the Heads fire broke out in the forward hold; the captain ran her into Nepean Bay and beached her, where she rolled onto her starboard side and burned – 'the port side was burnt to the copper'. Everyone was saved and the gold recovered. A court of inquiry found the fire had been deliberately lit.

The Scuba Doctor listing describes a site 150 m long and 50 m wide in 3–7 m with the bow to the south-west. Two mounds of bluestone ballast flank it. Between them lie the keel, hull frames, planking and copper sheathing, three large iron tanks amidships, and toward the bow a chain mound, another tank, an anchor marking the stem and several iron buckets. An information plinth installed by the Maritime Archaeology Unit stands on the starboard side near the tanks. The timbers carry kelp and sponges, the ballast mounds shelter crayfish, wrasse and leatherjackets, and rays and cuttlefish use the sand between.

As a dive it is shallow, sheltered and easy – an Open Water site in the calm of Nepean Bay – and as an archaeological site it is one of the most important in Victoria, the largest of the McKay clippers surviving anywhere and a protected historic shipwreck. Nothing may be disturbed, and the ballast and frames should not be touched. It is dived at slack or on the flood, when any drift sets along the shore toward Portsea.

Boat access only – Point Nepean is a national park and the listing notes that shore diving is prohibited from the point. Charters from Portsea Pier (Dive Victoria Group, Bayplay) are 5–10 minutes west along the shore; Red Boats from Queenscliff about 15 minutes across the entrance. Private boats launch at Sorrento Boat Ramp (Point Nepean Road, all-tide, trailer parking) and run 15 minutes west past Portsea.

Nepean Bay is shallow and the boat anchors on sand outside the reef line or holds off; a dive flag is required and the pilot boats and ferry pass close to the bay. The site is marked underwater by an information plinth placed by the Maritime Archaeology Unit on the starboard side near the iron tanks; boats anchor on sand clear of the ballast mounds.

Nepean Bay is 'sheltered from all winds except northerlies' (Scuba Doctor) and is the standard fallback when the Heads are unworkable, but the tide still runs through it: the Parks Victoria guide advises diving these reefs on the ebb, when the outgoing tide leaves the bay in relatively still water and any drift sets back toward Portsea rather than out through the entrance. Slack water at Port Phillip Heads does not coincide with high or low water: it falls roughly three hours after high or low water at Point Lonsdale, and the usable window is typically 20–40 minutes. Use the Ports Victoria / Port of Melbourne slack-water predictions for The Heads (also republished by charter operators and WillyWeather 'Rip Bank') rather than a standard tide table.

A northerly over about 15 knots puts a chop on the bay and cuts visibility; swell has little effect. Diveable year-round; clearest in autumn. Water 12–13 °C in winter, 17–19 °C in late summer.

Scuba Doctor lists it for slack water or the flood, unlike the rest of the bay – the flood sets divers along the shore toward Portsea rather than out of the bay.

Anchor on sand and descend onto the plinth at 5 m. Work forward along the keel past the three iron tanks to the chain mound, anchor and iron buckets at the bow (south-west), then back along the opposite side over the frames, planking and copper sheathing to the two bluestone ballast mounds; a full circuit of the 150 m site takes 30–40 minutes at 3–7 m.

Dive Victoria Group and Bayplay (Portsea) – occasional, often combined with a Nepean Bay dive or a wreck-specialty course; Red Boats – on request; Maritime Archaeology Association of Victoria monitoring dives.