Many of the better dive ops will try to group divers of similar skill levels together. That way no diver feels like they are being pushed beyond their comfort level and likewise no diver feels like someone else in the dive group is detracting from their dive. Frankly I wouldn´t dive with anyone who didn´t differentiate divers based on their skill level. Can you imagine going to a language class where all students were in the same class regardsless of their level of fluency?
Using Coconut Tree as an example, their 9am boat consists solely of divers who have had a check out dive on one of the afternoon boats before. That way they can make sure all the divers are capable of doing the morning dive they plan. Air consumption being a key factor, when you aim for a 50-60 minute dive with an avergae depth of 60ft.
Whether or not you actually have an AOW certification or not is not the issue, I know AOW certified divers that I wouldn´t allow on a morning advanced trip, and i have taken many divers on the morning trip who only have their OW cert. I never take anyone who hasn´t had a shallow relaxed check out dive though! When you read AOW consider that to be a comfortable level of diving NOT a piece of plastic saying you have done 9 dives!
Due to the fact that most Roatan visitors arrive on Saturday, Coconut Tree does a 9am dive on Sunday which does not require a check out dive. Since for nearly everyone this is the first dive of their holiday and after a break from diving it is only good sense to keep it shallow anyway.
