Launch your inflatable off the beach and head east until you see the two rocks (cow and calf?)
On a good day the viz can be 10 metres
This site has some tropical looking fish like rainbow wrasse that I haven't sen on other sites.
Further off the reef there is a coarse sandy bottom with interspersed rocks
Nearest air is Weymouth. Loads of campsites around. Like Osmington Mills (with the fantastic Smugglers Inn nearby)
Facts about Calf Reef, Ringstead Bay, Dorset