Manly Bommie is the outer extension of the Shelly Beach reef system, a stand-alone block of sandstone that Diveplanit describes as a 'shallow, squat bommie 50 m offshore' with a rectangular plateau of rock on top. It sits just outside the sheltered water of Cabbage Tree Bay on the ocean face of the Shelly headland, still inside the aquatic reserve boundary, and it rewards divers who have done the beach dive many times and want the reserve's more dramatic side. The plateau is 6–8 m deep and carpeted with kelp; its edges fall as short walls and stacked ledges to a sand floor at 12–14 m, and the shaded faces carry the sponges, sea tulips and bryozoans that the inner bay largely lacks.

Because it is exposed to open-ocean water, fish life here is bigger and denser than on the beach: schools of yellowtail and sweep over the top, kingfish passing in summer, blue groper, red morwong and old wives under the ledges, and wobbegongs, Port Jackson sharks in winter and the occasional eastern blue devilfish in the undercuts. Weedy sea dragons, which have largely disappeared from the inner bay since the March 2022 swells, are still occasionally found in the kelp around the bommie. Giant cuttlefish and octopus use the cracks.

The difficulty is entirely logistical. From shore it is a long surface swim over shallow reef and around a headland that breaks in any swell, and the exit is back at Shelly Beach; from a boat it is a five-minute drop from Manly Cove and the easiest dive of the day. Vizzbud's description of an offshore pinnacle to 28 m appears to refer to a different feature and should be disregarded.

The bommie suits confident Open Water divers with a guide or local knowledge, and it is a good option when North Head is too rough for the outer sites but the bay is calm.

From Manly Wharf follow Marine Parade around Fairy Bower to Shelly Beach (10 minutes on foot; two-level paid car park at Bower Street, $7–8/hour, full by 8 am on weekends). Enter at the northern end of Shelly Beach, follow the reef out around the Shelly headland (the ocean side of the aquatic reserve) and the bommie is about 50 m off the point – a 250–300 m surface swim each way that is only sensible in flat seas. Boat operators from Manly drop divers directly on it in 5–10 minutes.

Exit back at Shelly Beach; there is no exit on the headland rocks.

On the exposed outer corner of Cabbage Tree Bay, the bommie takes any swell from the north-east, east or south and is washed by surge even when Shelly Beach itself is calm. Attempt it from shore only with swell under about 0.8 m and no strong sea breeze, on the top half of the tide to shorten the swim over the shallow reef. Visibility mirrors the bay: 10–15 m on winter westerlies, 3–5 m after north-easterlies or rain.

Summer weekends bring heavy swimmer, snorkeller and boat traffic across the swim route.

Swim out on the surface along the Shelly headland reef and descend at the bommie. Circle the base at 12–14 m anticlockwise, looking under the overhangs for wobbegongs, PJ sharks and blue devilfish, then rise onto the plateau at 6–8 m to finish. Return underwater along the headland reef toward Shelly Beach as your safety stop, keeping the reef on your left.

Dive Centre Manly guides experienced divers to the bommie from Shelly Beach in calm weather and includes it on boat dives; Pro Dive Manly and Sydney Dive Charters occasionally use it as a shallow second dive. Otherwise independent divers and freedivers.