Ranelagh Beach is the private-feeling cove below the Ranelagh estate at Mount Eliza, distinguished by its row of colourful beach shacks and reached by a track from the end of Earimil Drive. The Scuba Doctor lists it as a 0–6 m shore dive with points of interest at both ends of the beach and access to Cahills Reef, which is marked by a beacon offshore. It is a close cousin of the two Daveys Bay sites 1.9 km to the north-east: shallow, sheltered on the right wind, and built around low sandstone reef with small ledges and boulder piles at the points and a beacon-marked reef out from the beach.

The reef and points hold the small-fish community of the eastern bay – southern hulafish, bullseyes, magpie perch, old wives, leatherjackets and moonlighters – and the rocks hide decorator crabs, hermit crabs, small octopus and abalone, while the sand between reef and beach carries seagrass patches where fiddler rays, stingarees and flathead settle. Cuttlefish visit in winter and squid at dusk. Cahills Reef is the deepest and most rewarding part of the site but it is an open-water swim through a stretch of coast busy with jet skis and boats in summer, which is why the source's only explicit warning is about traffic and a flag.

Ranelagh has no facilities and limited residential parking, and it is too shallow to interest experienced divers looking for depth; what it offers is a quiet, scenic beginner and snorkel site on the Mount Eliza cliff coast with a definite objective in the beacon reef. It suits new divers, families snorkelling from the shacks, and Frankston-area divers who want a natural reef within fifteen minutes of home.

From the Nepean Highway or Mount Eliza village take Earimil Drive west through the Ranelagh estate to the small car park at its end above the beach. A track leads down to the row of beach shacks on the sand – a walk of about 100 m with a moderate climb back. Enter from the beach and swim toward either rocky point, or out to the beacon that marks Cahills Reef offshore.

Exit back onto the beach. Parking is limited and residential; be considerate on summer weekends.

Ranelagh Beach faces west-north-west and takes westerly and north-westerly chop straight in, which stirs the sand and makes the shallows opaque; it is partly protected from southerlies by the Mount Eliza headlands. Dive on easterly through light southerly winds and near high tide for depth over the inner rocks and the reef. No current.

Run-off after rain clouds the cove for a day or two. Jet skis and boats run close along this shore in summer – the source warns specifically about them – so a towed flag is essential.

Enter from the beach, surface-swim toward the beacon towing a flag, descend on Cahills Reef in 4–6 m and circle it, then return toward one of the rocky points and follow it back to the beach in 2–3 m. Alternatively work one point out and back if the beacon swim is too long for the conditions.

No regular operator – local snorkellers and independent divers; occasionally Frankston dive shops for introductory dives.