Thanks "Water Buffalo"!
To answer your questions:
-There are 2 charters that do Black Water Dives in the West Palm Beach area. One is Walker's Dive Charters and the Other is Pura Vida. They are both excellent and they have an alternating schedule for which company is going out on a given night.
-Depth - We go out into the Gulf Stream where the actual ocean depth is 600 - 700 feet - but the divers stay mostly in the top 50 feet with occasional excursions deeper if pursuing an interesting subject. While the current is moving quickly - you have no visual frame of reference, so it doesn't feel like it - we usually drift between 5 & 11 miles during the dive.
-Length of Dive - Walker's allows 2 hours for the dive before you need to be back on the boat (air time permitting) and Pura Vida wants you back on the boat in 90 minutes.
Let me know if you have any other questions.
Heyward