arkstorm
Contributor
I recall that story from about 10-15 years ago.
- A down current was reported to have swept three experienced divers to 400 feet in Cozumel, eventually resulting in a DCS fatality. It eventually turned out to be a hoax. They claimed it was a down current to hide the fact that they had intentionally planned a dive to 300 feet (and accidentally gone to 400 due to narcosis.)
I wouldn't want to relegate the issue of down-currents to a conspiracy theory but there is evidence that many so-called down-current incidents are actually something else.
Cozumel seems to be ground zero. This would make sense given the prevailing current in that channel and the DM's there tend to have it on the mind. However, incidents like the one brought up by boulderjohn require us to be at least slightly skeptical.
Having said that, the question of what to do if caught in a vertical rip, do you move away from the wall or towards the wall...
The concept of laminar flow would suggest moving toward the wall because the friction of the water along the wall would slow it down compared to the layers of water flowing further from the source of resistance.
I would cling to the wall and try to work my way perpendicular to the flow until, hopefully, I got out of it.