I'm a little confused by all the scuba classes offered by PADI. I just got my open water and would like further training. Do I have to take Advanced OW before I move on to the specialty classes?
PADI lists 26 different, standard specialties. In terms of the prerequisites and certification levels...
2 specialties have no prerequisites and can be taken by a non-diver.
1 specialty has a prerequisite of Scuba Diver certification.
16 specialties have a prerequisite of Open Water certification.
2 specialties have a prerequisite of Adventure Diver.
5 specialties have a prerequiste of Advanced Open Water certification.
So right now as an Open Water diver 19 of the 26 specialties are avialable to you. Please note that some of the specialties have age requirements and/or additional certification prerequisties (like you need to complete Enriched Air specialty before taking the Rebreather specialty).
What is an Adventure Diver
I like to describe Adventure and Advanced as test drives of specialties. In Adventure, you get to test drive three types of dives. In Advanced, you will test drive Deep, Navigation, and three others.
Adventure can also be a stepping stone for Advanced. Here are a few of scenarios:
1. You want to become Advanced, but you really don't want to Deep in a dark, cold quarry, and you really want to take Fish ID in a tropical location. So you do Navigation, Wreck, and Night at the local quarry. Congratulations you are an Adventure Diver. Now you go on vacation, and complete Deep and Fish ID (with an instructor). Fill out some new paperwork and congratulations you are an Advanced Diver.
2. You sign up for Advanced class. You are freaked out by the dark, cold Deep dive. No way in heck are you doing that dive. Well, the weekend isn't a complete loss, you can still walk away with the Adventure Diver certification. (See #1 to complete the Advanced)
3. PADI only allows three training dives in a day. You are on vacation or your work schedule only allows you to dive one day. You complete three dives and you get the Advenure certification. You can come back later to complete the rest for the Advanced.
Am I allowed to do deep diving just by getting my AOW certification or do I have to complete the Deep Water class too?
With only an Open Water certification, PADI recommends that you dive no deeper than 60 feet. Once you get more experience or training (i.e. AOW), PADI recommends that you dive no deeper than 100 feet. With further training (i.e. Deep Diver) or experience you can dive to the recreational limit of 130 feet. There are plenty of divers with one Open Water certification that over time have developed the experience to go to 130 feet without needing the training.
There are some dive operators that will require a certificaiton. Simply stated: their boat, their rules. Worst case scenario, talk with them and see what they say.