A chart showing the location of Great Detached Reef (bottom right) and Thursday Island (top left)	Great Detached Reef - Da Phat is located only a little bit to left of the mark (6MP)

Great Detached Reef is a reversed C shaped reef made up of a number of separate sections. It is located a little off what is the main outside section of the Great Barrier Reef, although here that reef is merely a series of small bommies or reefs. Great Detached Reef is 11.5 nm from north to south and 8.8 nm east to west. The west (open) side of the reef has a series of bommies and small reefs along a large part of its length.

There are only a couple of boats that travel to this area, one being Kalinda which routinely does full boat charters there in November and December. Another boat does some trips there and one more might go there once or twice a year.

Kelly and I travelled here in November 2016 on Kalinda with fellow members of St George Scuba Club when we chartered the whole boat. We flew into Horn Island (next to Thursday) and started our trip from there.

Da Phat is a bommie located on the western side of the Great Detached Reef lagoon. This side is mostly open but along this side there are a series of small reefs and bommies that runs from almost north to south. Its location is approximately GPS S11º 43' 33.0" E143º 57' 38.4". It is about half a nautical mile from another brilliant site, 6MP. The depth on the top of the bommie is about 13 metres and from here it slopes drops steeply to 40 metres and then to 200 metres.

The site was discovered by Dave Stewart, owner and skipper of Kalinda. He was motoring in towards 6MP when his sounder all of a sudden came up from 200 metres to 13 metres. He later dived it and exclaimed it was "Da Phat" (or perhaps similar but X-rated words) when he surfaced. I believe that one other operator calls it OMB (Oh My Bommie) as the description of that site matches Da Phat (I hate it when competing dive operations won't agree to use the same name for a dive site).

This dive cannot be done as an anchored dive as it is far too deep for any boat to anchor. We did it by anchoring at 6MP and half the boat doing Da Phat by tender while the other half did 6MP. We then swapped for the next dive.

A huge school of long-finned bannerfish with other species - on the top of the bommies

The bommie is basically round and it only takes a few minutes to circle it. On the western side the depth goes to 200 metres a short distance off while the eastern side is only 60 metres!

We dropped down a shotline to the top of the reef and then down the northern side to about 30 metres. We spend a little time down here before coming up to 25 metres and then starting a gradual spiral around the main part of the reef. The actual bommie has a big split in the middle, meaning there are actually two top sections. The shallowest one is about 13 metres and the other about 15 metres. The split's bottom is 22 metres on the western side and 20 on the eastern side.

You can easily swim through the split, it is wide enough for a couple of divers to go side by side. On the (I think) northern bommie there is a large cave which has a tunnel through to the bottom of the split. You can swim into the cave and probably could go through the tunnel, but it is a little tight.

	Kelly below me on the wall
Kelly on top of one of the bommies	The split in the top section

The wall of the bommie is extremely vertical, it even undercuts in some spots. The wall has lots of smallish gorgonias and sea whips. There is also a uge amount of soft and hard corals, all in excellent condition.

The fishlife on this dive site is amazing. There are huge numbers of fish including dog-finned tuna, unicornfish, parrotfish and heaps more. The top of the bommie has thousands of long-finned bannerfish and we saw a few large firefish. There is also all the normal tropical fish. The top of the higher peak has heaps of anemones and clownfish.

An anemone with pink anemonefish	A close up of a pink anemonefish from the anemone at left

As the top of the reef is 13 metres, you need to ascend up the shotline to do your safety stop. Even here it was quite interesting as there were fish all around us the whole time.

We dived here in November, the water temperature was about 28ºC, visibility about 30 metres. A brilliant dive site.