Old Man's Shoulder is the eastern neighbour of Old Man's Hat, a couple of hundred metres closer to the Heads along the inner cliff of North Head, and it is a boulder dive rather than a wall dive. Here the bottom rises from 27 m to less than 10 m in a very short distance, but instead of a continuous face the reef is made of huge boulders and larger rocky sections tumbled from the cliff, with overhangs and cracks formed where they meet, one or two small swim-throughs, and sandy patches between the rock piles. The wall top is about 13 m, the deeper sections 24–25 m, and sand at 26–27 m.

The mobile life is the strength of the site. Weedy sea dragons are frequently encountered on the sandy fringes, wobbegongs lie in the cracks and between the boulders, and huge bull rays cruise the sand, one measured at two metres across. Black-reef and six-spined leatherjackets, kingfish, cuttlefish, squid and yellowtail are all regular, and hundreds of one-spot pullers and ladder-finned pomfrets shelter among the boulders.

The fixed growth is thinner than at the Hat but the deeper faces still carry sponges and sea tulips. Because it is inside the Heads on the harbour side it shares the Hat's great virtue of being diveable in a north-easter, and its slightly greater depth makes it a natural Advanced or Deep-training site for the Manly operators. Currents are usually mild and visibility averages 10–15 m, reaching 25 m on winter westerlies; the surface can look dirty while the bottom is clear.

The site lies within the North Harbour Aquatic Reserve. It suits Advanced divers who like boulder scenery and rays, and it is often dived as the deeper first dive before the shallower sponge gardens to the west.

Boat only. Dive Centre Manly loads at Manly Cove beach beside the wharf; Pro Dive Manly and Sydney Dive Charters load at the Little Manly boat ramp (end of Stuart Street, Manly – free parking, set-up benches, toilets at the reserve); Sydney Dive Charters also picks up at Rose Bay public wharf. From Manly the run is 10–15 minutes across North Harbour to the inside of North Head, 20–25 minutes from Rose Bay.

Private boats launch at Little Manly, Roseville Bridge (Middle Harbour, 30 minutes) or Rose Bay. Boats anchor on the reef in 15–20 m or run in toward the cliff and drop the anchor when the bottom appears; there are no moorings, and many abandoned anchors litter the reef. For Old Man's Shoulder run in toward the cliff about 200 m east of the Hat until the sounder rises abruptly from 27 m to under 10 m and anchor in the deeper section (33°49.31'S 151°17.39'E WGS84).

The inner face of North Head is the most sheltered ocean-quality diving in Sydney. It faces west-south-west into the harbour, so it is protected from the north-east sea breeze and from northerly and easterly swell, and is at its best when a strong north-easter is blowing and every ocean site is rough. It is exposed to southerly swell rolling through the Heads: a big southerly (over 2 m) sends surge along the cliff and dirties the water, though the deeper sponge gardens are usually still diveable.

Tidal current runs along the wall, east on the flood and west on the ebb, strong enough to plan a drift; slack water is easiest for novices. Visibility is 10–15 m on average, 25 m on winter westerlies, and drops after heavy rain when the harbour flushes brown. Ferry, shipping and small-boat traffic through the Heads is constant – ascend on the anchor line or a DSMB close to the cliff.

Anchor in 24–25 m. Head south past the wall for about ten minutes at 24–27 m along the boulders and sand patches, on the tide (east on the flood, west on the ebb), then come back shallower at 15–18 m through the overhangs and cracks between the boulders, and finish with a safety stop at 5–6 m among the shallow boulders above the wall.

Dive Centre Manly – double boat dives most weekends and some weekdays from Manly Cove (10–15 minutes); Pro Dive Manly – weekend double boat dives from Little Manly; Sydney Dive Charters – guided double dives Thursdays and Sundays from Little Manly ramp and Rose Bay wharf; Frog Dive, Abyss and Dive 2000 on club/charter days. North Head is the default Sydney boat dive when ocean sites are blown out.