Hi Cameron - great questions - actually made me stop and think for a moment.
Before I respond though, I think that most of the instructors on SB seem to hold themselves to a higher standard than the general population of instructors. So with that in mind, I would probably say the majority here are more likely to offer well taught OW classes, which probably would qualify as decent preparation to 100' (30m). As you point out, not all OW is a 3 day buy a cert course - but that is the standard - so when I posted above, that is what I had in mind.
Speaking of no magic cutoff depths, I saw one of John's posts in another string:
and I noted that I have felt pretty much the same way about the 60-70' depth range. Even 80' doesn't seem that much different than 60' to me, so there wouldn't be much difference between how I did an 80' dive versus 60'. But there are some differences I would start to consider for deeper than 60'.
Some background - I dive primarily in southern california, so the water is cool. so one of the first differences I would suggest, to my students wanting to dive depths deeper than 60', is a drysuit. Personally I dive dry in anything colder than 80 degrees f - especially if venturing deeper than 60' - which is often. Next I would add nitrox and smb. I would also add navigation. Even in my own classes - which I consider to be well taught, and are always longer than a 3 day buy a cert course, I would say many of my students aren't immediately ready to be at 100'. They could do it, as I'm sure many of our sb colleague's students could do it, but just not with the refinement that comes with experience and additional coaching (which is not reflected in an ow card).
Regarding trimix, I have become more and more of a proponent of 100' END (counting O2 as narcotic), although that is a sliding scale as well. I would't say narcosis becomes completely debilitating at 100', but I can tell I have to try and think much harder when I recalculate for changed dive plan even at 90'. For me I feel like trimix noticeably benefits me past 115', but I teach 100'.
I used to think I was perfectly capable of diving deep air when I was doing 200'+ often back in the day, but when I switched to trimix, I realized how much I was missing! It was like going from black and white to color!
Anyway - there is no specific magic depth where something happens - I just think if one is aware and honest with oneself, you can notice narcosis - co2 or otherwise - at much shallower depths than the cavalier diver would like to admit ... and while one can learn information that is good to know for deeper diving from SB and other sources, and one can even extrapolate what they learned from a well taught OW course for use in deeper diving, it is my humble opinion that there is no replacement for well taught additional training ...
- cheers
