What is proper procedure for downcurrent

[TTSkipper]

I have never dove anywhere with a down current and I was wondering what the proper procedure is for getting out of one? I would think that the best thing to do would be to swim horizontal out off the current rather than try and fight it and swim up. Similar to swimming perpendicular to the beach when you get caught in a riptide. Is this the correct plan?

This questions is in response to another thread regarding Nitrox and possible downcurrents.

Thanks,

TTSkipper

 

[Doc Intrepid]

I have never dove anywhere with a down current and I was wondering what the proper procedure is for getting out of one? I would think that the best thing to do would be to swim horizontal out off the current rather than try and fight it and swim up. Similar to swimming perpendicular to the beach when you get caught in a riptide. Is this the correct plan?

TT,

I can't speak to all downwellings universally, but those I'm familiar with occur as a result of tidal changes. Many South Pacific islands surrounded by reefs experience slight downwellings where the water recedes through cuts in the reef at low tide. Occasionally, due to islands being in close proximity to one another and/or other geologic/reef configurations, a great deal of seawater moves rapidly through constricted areas in the reefs as the tide recedes. As the receding water cascades over the edge of the reef, it can create a downward effect along the wall of the reef. High winds can also pile waves onto the reef, that then find their way back out through cuts in the reef. If you're trying to get in through the same cut, it can become a 'grab and hang on, then pull like hell' operation pretty quickly.

Should you encounter this, which is pretty unlikely, one option is to simply grab onto the wall and work your way up. Another option would be to blow a bag on a reel. (I've never gotten caught in one, but did a drift dive in Palau that involved dropping into a channel in a reef between two islands as the tide was going out. The receding tide pulled us along at a pretty impressive rate, but we surfaced and boarded before going beyond any edge of the reef.)

While there may be much more to downwellings than this, I would think that any charter operations would be aware of hazards in their area and eager to avoid them. I suspect your chances of experiencing something traumatic are fairly remote.

FWIW,

Doc

 

[MB]

I have never dove anywhere with a down current and I was wondering what the proper procedure is for getting out of one?

I've watched people swear about the best way, but as usual, it all depends. In this case, it depends on the conditions that caused the current.

In Coz, there is sometimes a phenomenon where currents cut across the shallower, flat reef, and when that water reaches the edge of the reef (the dropoff), the current "falls" downward. This means the current is now pushing divers down, rather than horizontal along the reef ledge. Bummer.

One way to get out of that is to get away from the ledge. By moving some distance away from the reef, the strength of the down current dissipates. Problem: you are now out over blue water, where the bottom might be 3000+ feet. OK, not a problem if you are psychologically prepared for a blue water dive.

A second way is to get closer to the ledge. By becoming one with the reef, the spilling current will move across (over) you, as it moves across the reef itself. This requires the diver to get very close to the reef itself - meander 4-5' away from the edge of the reef, and you are right smack in the middle of the strongest part of the current.

A third way involves waiting. Some of these currents are quite transitory. Hold on, and wait a minute or three and they shift, and the diver can go on his or her merry way.

The "climb up the reef method" mentioned in a reply above will also work, but at some point, the diver reaches the top of the ledge, and once again faces the current that is cutting across that reef. But the climbing technique can at least get one away from the deep water and up the the reef top, which means you're part way home. But then you still have to pick one of the three metrhods above.

These methods all relate to the downcurrent caused by the current splilling across the flat reff, with water plunging toward depth. Other reasons for the downcurrent may have other solutions.

 

[Michael Schlink]

Having been in several "downcurrents" myself, most recently in Indonesia in Dec. There are several things you can do and a couple you must do. 1. don't get pushed down too deep too fast. So slow or stop your descent by; inflating your BC, finning, use a reef hook if you have one and holding onto the reef if that's all you got! 2. Check your air supply and deco status so that you can decide if you can try to wait it out. Some will play out some will last longer than you can. I have been in currents that crawling up the reef would have been difficult at best. 3. Get control of the situation and decide how you are going to proceed. Make a decision IE; wait 5 min. and then try to swim out of it, crawl up the reef or swim out away from the reef. You really only have a few choices. Swim up, swim out, wait a little and hope it plays out. "Shooting" a lift bag's not an option, so don't bother trying. I do reccommend carrying a "sausage" (6-10', not the little 4') and a small reel (spool). Then if you pushed back off the wall you can inflate your "sausage" and do a nice little safety/deco stop and surface support will know where you are. Dive Safe-Dive Alot-M

 

[SDAnderson]

A second kind of down current occurs where an open water current meets an obstacle and the flow divides, splaying out in many directions like the stream from a hose hitting a wall. I've been caught in one of these in Hawaii a couple of times and it's a thrill, to say the least. The backside of Molokini is a blue water wall with the first shelf at about 300 feet. The wall faces a channel that leads to the open ocean and when the current is coming in just "wrong" it can easily crank up to several knots. A slight shift in the wind can mean a spectacular plunge.

If I remember my math correctly, each knot of current works out to something more than 100 feet per minute, thus a 3 knot current can drag you down 100 feet in less than 20 seconds. Yoikes!

Solutions for this kind of down current:

• Reverse course. What ever direction you were coming from is the direction you want to swim, in an effort to find the way out of the current. Turn around and fin hard. You won't immediately stop descending but you can't outswim a hard current, only hope to escape from it.
  
• Do not drop your weights. When the elevator ride ends, you are going to need that weight to avoid a rocket ride to the surface.
  
• Hit the inflator button and don't let go until you stop descending. Boyle's Law will keep your BC from over-inflating until your descent slows - that disgusting burping sound that comes from an overfull wing will be very comforting.
  
• Be prepared to dump air from your wing as soon as your descent slows. Absent the downward thrust, you are going to find yourself way positive and need to do something immediate to get neutral again.

I've seen folks grab ahold of the wall and hang on and it works - sort of. The force of the current blew one guys mask off his face and another guy had his tank slip through the bands. It seems to me like this is making three problems out of one and I'd rather not.

The first time this happened to me I was at 50 feet when I got hit by the current and dropped to 140 before I was able to recover. I can't tell you how long that took, just that at the time it seemed like both an instant and an eternity. At any rate, it wasn't more than a handful of seconds of watching the wall and my life flash by. The second time I acted more quickly (maybe the current wasn't as strong) and only dropped about 50 feet before I escaped.

Not just for the pelagics is that dive now a must-do on every visit.

 

[Uncle Pug]

Currents can be helpful if you use them to take you where you want to be. Down currents are currents. Therefore down currents can be helpful if you use them to take you where you want to be.

Best bet is not to fight any current but learn how to use the current to go where you want to go.

Of course a lot of folks don't get much practice in between vacation dive trips.

 

[Michael Schlink]

I guess if you want to go down, in a hurry, than a "downcurrent" is just the ticket!

 

[Cave Diver]

I guess if you want to go down, in a hurry, than a "downcurrent" is just the ticket!

I wonder what kinda descent rate Pug can get with his scooter in a down current? :54:

 

[RSoper]

Talking of currents i thought you guys (and girls,) may find this article about the Corryvwreckan Whirlpool in the UK, off the north west coast off Scotland, interesting. It is arguably one of the most challenging dives in the UK, i have not dived it myself, would any of you with drsuits be willing to give it a go?!

www.ukdiving.co.uk/ukdiving/sept/corry1.htm

 

[Walter]

MB was in a downwelling in Cozumel a few years ago in which some folks inflated their BC's to no avail. It merely gave the current more area on which to push. Two of the folks on that dive had video cameras. Bubbles were heading down! Sometimes the currect is too strong for the BC to lift you against it.