Advanced Bommie is, as the name implies, a site for experienced divers. Scuba IQ describes two huge towers surging up from the seabed at 40 m, separated by a deep gutter, and calls it one of the sharkiest spots they know. It is one of the deepest and most dramatic dives on the Agincourt complex.

The two towers stand side by side on the seafloor, their walls covered in hard corals, sea fans and soft corals. The gutter between them is deep and narrow, creating a channel that funnels water and plankton, and it is here that the sharks congregate – grey reef sharks and whitetips circling the base of the towers and cruising through the gap. Schooling fish crowd the upper parts of the towers, drawing trevally and other predators.

The depth is the defining feature. With the seabed at 40 m, divers must carefully plan their maximum depth and bottom time. Most divers stay in the 20–30 m range, descending to the gutter only briefly before working back up the towers.

Good buoyancy control is essential, and divers should be comfortable with deep diving – hence the site's name and its restriction to advanced-certified divers. Visibility is often excellent, which helps with the sense of scale: looking up from the gutter at the towers with sharks overhead is a memorable sight. Current can run between the towers, particularly on stronger tides.

Advanced Bommie is ideal for divers who want a deep, shark-focused dive on the outer reef and have the certification and experience to do it safely. Nitrox can extend bottom time at moderate depths, but watch your maximum operating depth. For many divers visiting Port Douglas, this is the dive that delivers the most sharks.

Agincourt day boats leave Crystalbrook Superyacht Marina (formerly the Reef Marina) on Wharf Street, Port Douglas, between about 8:00 and 8:30 am. Park in the marina car park or the free all-day street parking around Wharf and Dixie streets; Quicksilver, Poseidon and Calypso also run coach pick-ups from Port Douglas, Palm Cove and northern Cairns beaches. The run to the Agincourt ribbon reefs on the edge of the continental shelf is about 65–70 km north-east and takes roughly 75–90 minutes on the large catamarans (Silversonic is the fastest), longer on small-group boats such as Scuba IQ/Blue Dive.

You gear up on board and giant-stride from the dive deck at a permanent mooring; the skipper picks the sites on the day to suit wind and tide, so a named site is never guaranteed. Boats are back at the marina around 4:30 pm.

Agincourt is an outer ribbon reef on the shelf edge, so it is fully exposed to the south-east trade winds that blow from about April to September. Moorings on the protected western (back-reef) side remain diveable in 15–20 knots, but anything over 25 knots or a 2.5 m+ sea makes the crossing rough and operators may cancel or switch to more sheltered moorings. Calm spells in October–December give the glassiest days and 30 m+ visibility.

The wet season (December–April) brings northerlies, afternoon storms, cyclone risk and occasional reduced visibility after big rain events, although the outer reef is far less affected by run-off than inshore reefs. Marine stingers are present November–May. Tidal currents run along the reef edges and through the gaps between the Agincourt reefs; spring tides strengthen them, so exposed corners are usually dived on the neaps or near slack water.

Descend directly to the gutter between the towers at no more than 30 m (advanced divers), spend a short time watching for sharks, then work up and around one tower and across to the other. Ascend the tower sides gradually and do the safety stop on the top of the shallower tower.

Deep recreational dive; plan maximum 30 m; if using nitrox, EANx32 MOD ≈ 34 m, EANx28 ≈ 40 m (ppO2 1.4). Short bottom time at depth.

Scuba IQ / Blue Dive – small-group Agincourt day trips (max ~20 guests) several days a week; the site names are Scuba IQ's own and may not be used by the larger Quicksilver/Poseidon boats.