The Ham Luong, registration DK 06, was a 15 m steel Vietnamese refugee boat that arrived in Darwin in 1977. Like the other refugee craft that were impounded after their passengers were processed, she sat unused for several years before being prepared for scuttling. Between 1976 and 1981 more than 50 boats carrying Vietnamese refugees reached Australia's northern coast, most of them arriving in Darwin Harbour. Several of the steel boats were later cleaned and scuttled west of Cullen Bay together with a redundant construction barge to create a fishing and diving reef, and the site was extended in later years with a confiscated illegal fishing boat. The group sits in 20-25 m within a few hundred metres, and some operators have linked the wrecks with rope so that more than one can be visited on a dive. She was sunk close to the John Holland Barge and the Song Saigon (DSAC gives 1983; marinelife.org.au 1985).

The Ham Luong sits upright on the bottom in 21-25 m. She is small and simple, but four decades on the seabed have turned her into a compact reef, and the fish life is dense for the size of the structure: gropers, surgeonfish, black jewfish, coral trout, batfish, parrotfish and trevally are all recorded here, along with the golden snapper, cod and tuskfish that NT Fisheries lists for the complex. Interior spaces silt up very quickly, so it is a wreck to look at from outside. Because she can be seen in a single lap, the Ham Luong is usually dived in combination with the Song Saigon and the barge, and on a good neap it is possible to take in all three. It suits Advanced divers or Open Water divers with a guide who are comfortable at 25 m in limited visibility.

Boat only. The refugee-boat complex lies in the outer harbour a short run west of Cullen Bay - typically 10-15 minutes from Cullen Bay Marina or the Cullen Bay public ramp (off Marina Boulevard, trailer parking on site). NT Fisheries publishes the positions of each wreck for anglers, so expect fishing boats on the marks on neap weekends.

Drop a shot beside, not into, the structure, and plan to be on site before high-water slack; the complex is exposed to the full tidal flow once the tide turns.

Tide is everything in Darwin Harbour: the spring range is 7-8 m and tidal streams run hard through the harbour, so diving is generally only possible on neap tides (range under about 3-4 m), timed to the slack at high water when clearer ocean water sits over the site. Spring tides bring strong currents and silt-laden water with near-zero visibility. The dry season (May-October) gives the most consistent conditions; the south-east trade winds can chop up exposed water in the afternoon, so mornings are best.

In the wet season (November-April) run-off from the rivers and creeks drops visibility, afternoon storms build quickly, and the harbour is in cyclone season; box jellyfish are present October-May.

Descend on the NT Fisheries mark to the upright hull, circle it at 22-24 m and look over the deck. The boat is small enough to see in one lap, so use the remaining time to follow any connecting rope to the Song Saigon or the barge. Return to the shot for the ascent.

Darwin Dive Centre and Dive Darwin include the Vietnamese refugee boats and artificial-reef wrecks in their neap-tide harbour charters; Darwin Sub Aqua Club dives them regularly on club days. No fixed daily schedule - trips follow the neap cycle.