Shona Bay is just of Port Ghalib - used occassionaly by day boats, but often as an area to do your check dive for the liveboards. The bay about 350m wide allowing enough space for everyone even when several boats are moored up.
The current is prevailingly from the North pushing past the reef. The reef bay itself is well protected and has little to no current. Diving is done in the middel section and the two larger reef section to the West and the fringe reef to the road are usually not dived.
There are a number of ways to dive it, depending on your briefing. The most common one is to use the RIBs (Zodiacs) to get you to the northern edge of the reef and use the curent to push you back into the bay area. The area around the northern reef curve is only 10 to 17m deep, giving a pleasant drift back.
The other way to dive it, is to do a loop within the bay, diving on the Western side of the shelf, where there is no current at all. The third way is to just swim against the current (North) from the dive boat along the shelf (the current is very weak) until it becomes to strong as you turn the corner and expose yourself to the sea, just turn around and drift back to the boat.