This looks like an interesting dive to do - Racha Yai Island Dive - Phuket Thailand

The main problem at Racha Yai is that it is the island closest to Phuket with good snorkeling. This means there are often many speedboats and fishing boats, all mooring in the same area as the diveboats.

I therefor prefer the trip to Racha Noi and Racha Yai. 1 dive more for relatively little money, normally excellent visibility at Racha Noi plus at Racha Noi there is hardly anybody. By the time the trip reaches Racha Yai most of the other boats have left already.