Dealing with Downcurrents

[Dave Dillehay]

If you dive Cozumel often enough you are bound to encounter a downcurrent. That holds true for almost all the reefs that have walls. I actually believe that due to its distance from shore, that Barracuda is less prone to that than say Santa Rosa Wall

The downcurrents function exactly the way a rip tide/current does on the beach. In the case of rip tides, large waves wash up on the beach, sometimes joining and then rushing back out to see in a narrow band. All life guards will tell you to not fight the current, but to swim parallel to the beach and you will soon be out of the current, and can probably let a wave push you back in. It is those who continue to fight the current who get into trouble.

In Cozumel, during seasonal transition, like we have for the next few months, there are large eddies of open ocean currents that sometimes push large bodies of water up against the shore, raising the water level. But gravity prevails and that water has to rush back out to sea. Most generally that water rushes down thru cuts in the coral heads and can have a serious velocity. But like the beach rip tides, it is almost always a very narrow band and that is why you hear stories of divers 20 feet away not having the same problem.

As best I know, the downcurrents start to diffuse below 150 ft and normally are gone by 200ft. But that does not suggest that you just go along for the ride! The best bet is to do as your beach lifeguard told you. That is, to swim quickly across the reef and you will probably be out of it in 20 to 50 feet. They also may be difficult to detect but if you think you are swimming horizontally and all of a sudden you have to clear your ears, look at your depth gage and the reef rising above you!

We try to address this issue on every dive briefing, but especially at this time of year.


Dave Dillehay
Aldora Divers

 

[FishOutUvH2O]

All life guards will tell you to not fight the current, but to swim parallel to the beach and you will soon be out of the current, and can probably let a wave push you back in. It is those who continue to fight the current who get into trouble.

I read this and cringed. As a former beach lifeguard, that would be only part of what we tried to teach people. The other parts are that the rip current will not pull you under, and that swimming parallel to the beach right away may be the wrong answer. If, you can see the rip is wider than about 25 yards, or after a few yards of swimming parallel to the beach, you notice that you still have a way to go until you're out of the rip, and it's still pulling you out. STOP swimming and conserve your energy. Wait until the rip dies down and then swim in diagonally.

My, point, as I stated (or tried to) in the other thread about downwellings, is don't assume that there is a "one-size fits all" answer to how to deal with what the ocean can throw at you. If downwellings are anything like rip currents then they can come in many shapes and sizes and be outside of the bounds that even seasoned experts would've predicted (think rogue waves). Know that they can happen, and that if you're caught in one, to actually think about what your current situation (hey, I made a punny!) is and requires. To think that they're only going take you to X depth or only be X wide ignores a basic premise about the ocean; it is full of surprises. There's a reason that every Hawaiian child is (and every other child should be) taught to never turn their back on the ocean. It's because you can never tell what it will do.

This isn't meant to be argumentative, more supplementary. I think that what Mr. Dillehay is saying is great and applaud him for taking the time to brief people on it. I really just want to caution people against trying to using hard-and-fast "rules" to situations that apply to what the ocean can/will do. A little flexibility in responding to a situation may be called for. I grew-up around the ocean and as a life-long surfer I've ever only lived by one "rule" when it comes to the ocean: When in doubt, don't paddle out.

And here's a shameless plug for a friend: If you have the time and want to take surf lessons while you're in Cozumel, contact Nacho:Cozumel Surfing. I've yet to see any of his students not have a great time.

 

[skicolby]

Lots of good stuff in this thread and the other downwellings thread started by firstdive2005. These threads have been extremely useful for a newly-certified diver like me.

Some learning points that I have picked up from reading the threads are shown below. These may be obvious to more experienced divers, but I'll state them anyway 1) In areas where there are currents and structure, there WILL be vertical currents. As someone who has whitewater kayaked, I know that water in a river flowing over a ledge or a big rock will create "holes" and "washing machines". The same thing will obviously happen with ocean currents and underwater structures. Cuts in a reef are like sections of a river where it narrows and the water speeds up, so that is obviously a risky location. 2) Look for those kinds of features as you're diving as an indication of where you might find dangerous currents and either avoid them or anticipate a potential change in current and prepare yourself. When I'm backcountry skiing I'm always aware of the safety zones (ridgelines, etc.) in the event of an avalanche and before skiing a really steep chute I remind myself of how I will self-arrest if I fall. In diving a place with currents and structure, one always needs to be thinking "what would I do if I hit a vertical current here?". 3) Carry emergency locating devices at all times (SMB, flag, mirror, whistle, personal locator beacon, etc.) and don't take comfort in the divemaster having it if you don't because you could very easily be separated from the DM. Those things cost a bit of money but are far cheaper than paying the ultimate price 4) be very wary about diving near your depth limits in areas with strong currents because a down current could quickly carry you far deeper than you want to go before you have a chance to react. Not sure its a wise idea for even experienced divers to cruise along Barraduca wall at 125 fsw. Leave a margin for error. 5) carry enough air, and plan your dive to end with sufficient air, so you will be able to do the req'd decompression stops if you get swept deep by a down-current 6) dive with a reputable shop/DM that is intimately familiar with the area so they can steer you away from, or at least warn you about, the problem locations.

It would appear to be the case that the precautions I mentioned above should be adhered to at most dive sites in Coz, not just the north sites. Having just completed my OW cert in Coz, including dives at sites which are susceptible to the risks mentioned in these threads, this is a big wake-up call. I did dive with a reputable company and DM, we managed gas conservatively and stayed away from the edge of the wall when there was a strong current, but I personally omitted some of the other precautions (i.e. no SMB, etc.) and as a now-certified diver, that was MY responsibility. I will be diving in Coz again, but will certainly be much better prepared in the future and aware of the risks as a result of these posts.

 

[jfcl01]

I have been going to Coz for 10 years and these 2 threads are the first I have ever heard about downcurrents. How can that be?

The thought of being suddenly sucked downward 30+ feet has me re-thinking nitrox...that bother anyone else?

 

[Jax]

I have been once, and they briefed us on it.

Does anyone know if this is also an issue on the Playa Del Carmen side?

 

[RubberDucky]

I have been going to Coz for 10 years and these 2 threads are the first I have ever heard about downcurrents. How can that be?

I'd never heard of them either until I read numerous threads in the Accidents and Incidents section of this forum over a lengthy period of time. It's interesting all the things you can learn there that aren't taught by reputable diving agencies. One simple sentence about swimming parallel and up could save lives.

The thought of being suddenly sucked downward 30+ feet has me re-thinking nitrox...that bother anyone else?

I had this very realization earlier today, and decided that the risk of nitrox is far too great to ever consider. Perhaps under different dive conditions like quarries it would be ok, but in areas with the potential for strong currents? It's not worth the risk, imho.

 

[Dave Dillehay]

Just one added thought. Very few of the down currents ever reach the point of being dangerous, and many of you have probably been in one and never known it But if you see whirlpools around the boat or dive site...it would be wise to tell the DM or sit it out.


Dave Dillehay
Aldora Divers

 

[Cave Diver]

More info: http://www.scubaboard.com/forums/ba.../48956-what-proper-procedure-downcurrent.html

 

[geokr]

Got a question....do significant downcurrents provide any visual indication of how large they may be, such as sand being kicked up in them, to let you know what direction to move to get out?

 

[FishOutUvH2O]

Got a question....do significant downcurrents provide any visual indication of how large they may be, such as sand being kicked up in them, to let you know what direction to move to get out?

That's an excellent question. It brings up a point that I probably should've mentioned in the other thread. And that is the down-current/downwelling wasn't the only current in play. The usual north-heading current was also there. So, we were essentially being pushed down and north at the same time. So, in our case, going back the way we came to get out of the downwelling wasn't really an option. What I do remember about the downwelling current though, in terms of spotting it's width, was the fans hanging off of the side of the wall. Much like palm leaves they were being bent down and vibrating like crazy. Unfortunately, the visibility wasn't the best that day, maybe 30ft. Probably because of the currents. So, I really couldn't see how wide the downwelling was. But, to be honest, I don't know how accurate my observations of that day are, my focus was mainly on my wife, what I was grabbing, and above me.