Small Crack is located slightly north of the Dunraven on Sha'ab Mahmud. It is often used as an alternative dive sites and is also popular with dive instruction. We have used it in the past with students do their open water dives here, as the sandy lagoon with it 5 metres maximum depth offers a save environment for teaching.
The small crack or small passage is well defined and even visible from Google Earth (see photo on the right). The current along the crack tends to run north to south, so the RIB (Zodiacs) will drop you off up the reef and a slow drift dive back along the wall with a maximum depth of 25 metres will give most divers an hour dive or so. The bottom slopes away gently and the current does become stronger as you seem away from the reef.
There is a resident turtle on the north reef and you can generally find it, by looking out for it grazing on the coral (you will see a "cloud" of silt on the reef). As you approach the crack, check for the current. If the current is flowing against you, you can try by hugging the floor and pulling yourself along the sandy bottom to get through (we have done it once, but it was huge effort). If that happens, deploy your SMB just outside the crack and left the boats pick you up.
However, if the current is with you, slide along the crack with the current (careful it becomes shallow very quickly - so make sure you vent your BCD) and get pushed into the lagoon. The current works well behind the crack and if you stay about 1 metre above the sand, the current will easily carry you nearly to the boat without any effort.