Down currents

[Dave Dillehay]

...and just about everybody is diving nitrox

While being a dive guide I never used nitrox on a wall dive and would not condone it now, just in case I had to help someone who has gone deep. But most of my down current testing dives were in the 90s (at a much younger age) before nitrox was widely available. Now, since I own my own compressor shop and no longer lead dives, I do use nitrox all the time on every dive…at my age I have to make concessions.

BTW, one of the reasons I posted as I have, is to give divers a realistic opinion of what they might face in a down current. I hope to reduce panic as it is well known here that the two most common cause of dead divers is heart attack and PANIC.

In addition, I felt it was a responsibility of a dive shop owner to understand the way down currents work. Perhaps that was because in my previous life I was an investigative engineer. I evaluated the risk, was prepared for it and knew for certain that PADI did not revoke the c card of everyone who busted the 130 ft rule.

Dave Dillehay
Aldora Divers

PS Also, as a dive shop owner I felt it MY DUTY to inform divers as much as I knew about down currents…that should be hard to complain about.

 

[flyboy08]

Are down currents predictable? Is there a current pattern, weather pattern that causes these? Are there processes in place where dive shops share these phenomenons with each other when they are realized? Location, date and such?

 

[Dave Dillehay]

They can happen anytime but are more common in the late winter/early spring. That is when the current becomes more turbulent (Why? I don't know). They do not persist very long so it would be futile to broadcast. Frequently you can detect swirling water on the surface and decide to dive a different reef. One time we were in the boat getting ready to go and all of a sudden the boat started rotating rapidly, and changed our plans.

Dave

 

[ggunn]

I too have experienced a down current at Barracuda reef.

Yo tambien. It wasn't as extreme as other accounts I have read, but on the day in question the current was running at an angle with the reef and there was a waterfall where the current poured over the top of it. It was, as I said, not that extreme in force but big, pretty much pouring over the reef in a sheet a couple of hundred yards wide but not very thick. In that case, it was coming down the reef right down the wall and the way to get out of it was to move AWAY from the wall.

 

[northernone]

Yo tambien. It wasn't as extreme as other accounts I have read, but on the day in question the current was running at an angle with the reef and there was a waterfall where the current poured over the top of it. It was, as I said, not that extreme in force but big, pretty much pouring over the reef in a sheet a couple of hundred yards wide but not very thick. In that case, it was coming down the reef right down the wall and the way to get out of it was to move AWAY from the wall.

NII GEEH. That current induced waterfall I've seen a 9 times on Barracuda reef. Haven't encountered the powerful kind there yet.

I like the idea of this thread. Some publicly shared observations might help form an idea of the bathymetric factors that result in the particularly challenging forms of down wellings. There's tons of data points with all the divers but without some collaboration it's going to remain a mystery. Sure currents are unpredictable, but there are patterns as well.

For what it's worth, there's a local older man who can tell the days to expect those unpredictable currents and warns away from certain sites on those days were he most frequently saw them.

Could we formalize this. A map with regions decided up (reef names perhaps, but those are arbitrary) where we could combine our experience to tally where the down wellings are most common.

Thoughts?

Cameron

 

[flyboy08]

For what it's worth, there's a local older man who can tell the days to expect those unpredictable currents and warns away from certain sites on those days were he most frequently saw them.

Lets hire this guy!

 

[RayfromTX]

Sounds like a project for this winter's surface intervals.

 

[mmmbelows]

My nickers aren't in a twist Dave - No worries. However, no one should be thinking it's fine to just strap on a HP 120 and head deep to catch a buzz. That is decompression diving which is an entirely different from recreational diving within recreational limits .

Actually a 200 ft dive isn't necessarily automatically a decompression dive, the same as a dive only to 70 ft isn't necessarily a non-decompression dive, time at depth is the more important factor. I put more weight on 'diving within your limits' rather than padi benchmarks, especially when it's in regard to somebody with 10,000 dives of experience to draw from. Information is beneficial and I believe what the spirit of Dave's posting was.

Santa Rosa wall has so far been the only dive site I've experienced any of the signs of a down current. Seems to be the dive site most reported in my non-scientific sampling based on threads.

 

[Mr. Manfrenjensenden]

Thanks to all for your responses. Very helpful. No, I wasn't letting the idea of a down current scare me off, either before or after posting this. But, having heard about them, I wanted to know more. And now I do, so thanks.