Dealing with Downcurrents

[Mike]

So you're saying if the DM does a pre-check and the current is fast you sit it out on the boat and wait for the other divers to come back? I'm curious/confused because you said those two sites you'll take a pass on if the current is fast. In my experience and understanding the only way to know is when you're already over the dive site, so I guess you're saying you sit it out on the boat, cause they aren't taking just you back to shore or nor refunding you for the dive.

 

[Nanodiver]

I was in Coz last February- when we arrived at one of the far Southern sites (of course I can't remember which), our DM dropped in before the rest of us to check current strength and direction. He reported that conditions were OK- otherwise the boat would have taken us to another site. I was diving with.....Aldora. -Nancy

 

[Prop Joe]

How you gonna know?

When we go north (or where ever) the DM's have a pretty good idea of what to expect, as they know the seas. Some days they will flat out look into the channel and say "no way". We have however gone north for a rather pissy customer demanding to go north. When we arrived at Barracuda we suited up to have the DM jump in with his gear to check current. Captain drags the DM around hanging onto a rope, looking at the drop zone. The DM then said "no go", "not safe". It is his call. Off come the rigs. At this point we get the DM aboard and headed to one of the southern site(s). I think we did Cedral wall instead, I'd have to look in my log. This is one of the reasons I tip DM's well that look out for me. I'm all for having a good time, but I need to go back home and make some money so I can come back another day...

 

[farsidefan1]

So you're saying if the DM does a pre-check and the current is fast you sit it out on the boat and wait for the other divers to come back? I'm curious/confused because you said those two sites you'll take a pass on if the current is fast. In my experience and understanding the only way to know is when you're already over the dive site, so I guess you're saying you sit it out on the boat, cause they aren't taking just you back to shore or nor refunding you for the dive.

Why do you care? It's his call. If a person decides to call a dive for any reason they choose it is not up to anyone but themselves. They are grownups and can accept the "consequences". Sorry if I'm over reacting. Probably I misunderstood your intentions but it just sounded a bit condesending or demeaning to me.

 

[Mike]

Yes, you are miss-understanding.

Let's back up. He said he was going to add those dive sites to his list of dive sites that he would take a pass on if the current was too fast. I've dove those sites and I'm trying to understand what he means, because we aren't talking about a DM canceling the dive, obviously if the DM cancels the dive there is nothing to talk about, the poster is not diving that site whether he wants to or not. I'm asking him for friendly details because maybe he has different experiences than I, I've never seen a dive shop call ahead to a dive site to get a reading on the current and give customers a choice prior to the boat leaving the dock. Basically all I've experienced is you get on the boat and go out there and check once you get there. If that's the case and the DM checks and says it's fast but diveable, then the poster is I guess sitting on the boat?

I'm trying to understand his experience, because based on mine that would be the only way it would work and that's why I'm asking, is that what you're saying? If the DM checks the current and it's fast and he says lets go, you're staying on the boat? It's just a question I'm asking to see if there is possibly some alternative I'm not aware of, maybe he's diving with a dive op that operates differently then what I've experienced?

I don't see asking the question as being condescending, loosen your panties for Christ sakes, he's never even said what he does and nobody has said a word about anything even if he did. I don't think you've been called here to defend anybodies honor, especially when nobodies discredited anything. Can we relax for a second?

 

[DjDiverDan]

Yes, Mfinley, if the DM checks and says "the current is really quick, but diveable", I may very well tell him, "Thanks much, but I think I'll sit this one out," even if I'm not going to get a refund for a missed dive; the money is far less important to me than my own well-being. I'm old, fat, and not nearly in the shape I was 20 years ago when I started diving, but I hope to continue to enjoy diving for many more years. I'm not into diving for the adrenaline rush, but for the quiet solitude and relaxation of drifting over a beautiful reef and enjoying the wonder of the sealife, large and small. And I feel no need to prove to you, the DM, or anyone else, that I am "Man enough" to take a dive that's going to make me nervous or that I'm not going to enjoy. It's precisely the "macho", testosterone driven need to prove yourself to others or establish bragging rights that got those three unfortunate divers in Cozumel into so much trouble a week or so ago. So, Yes, I'll sit out a dive that I'm not comfortable making, and if that makes you think I'm less of a diver, go ahead and think that. I'll respect your right to have an opinion, if you'll respect my right to ignore it.

 

[cenotist]

I am sorry, to jump into this thread, but in my opinion the down currents are far less dangerous than the up currents. Instead of talking about getting down fast, it is far more relevant to talk about getting up fast and causing the helium/nitrogen/… bubbles in your tissues/blood/… to expand rapidly and cause thrombosis or other obstacles in your pipework.

To put this into some perspective: when you come up from 40 ft to surface, the diameter of gas bubbles is increased by 30%. It is the same as to go up from 400 ft to 165 ft. Or another: when you come up from 20 ft to surface, the change is +17%, the same as from 330 to 200 ft. I believe, that many of us will just pump our vests/wings full of gas and torpedo to the surface after safety stop without thinking, that they would never do it from 330 to 200 in 2-3 seconds.

My point is, that having at least some reasonable amount of reserve gas in your tank, you can easily swim out from any down current and finish your dive according to your computer. You will not be killed by extra 20...30…40 ft of depth, but there is much more danger involved if you are pushed to the surface from the depth by current or by your own flightiness.

Just a thought.

 

[old gaffer]

Yes, Mfinley, if the DM checks and says "the current is really quick, but diveable", I may very well tell him, "Thanks much, but I think I'll sit this one out," even if I'm not going to get a refund for a missed dive; the money is far less important to me than my own well-being. I'm old, fat, and not nearly in the shape I was 20 years ago when I started diving, but I hope to continue to enjoy diving for many more years. I'm not into diving for the adrenaline rush, but for the quiet solitude and relaxation of drifting over a beautiful reef and enjoying the wonder of the sealife, large and small. And I feel no need to prove to you, the DM, or anyone else, that I am "Man enough" to take a dive that's going to make me nervous or that I'm not going to enjoy. It's precisely the "macho", testosterone driven need to prove yourself to others or establish bragging rights that got those three unfortunate divers in Cozumel into so much trouble a week or so ago. So, Yes, I'll sit out a dive that I'm not comfortable making, and if that makes you think I'm less of a diver, go ahead and think that. I'll respect your right to have an opinion, if you'll respect my right to ignore it.

I could not agree more. I dove Punta Tunich last year and the current was the fastest that I had experienced in Cozumel. It made me somewhat anxious and with Punta Tunich not having a great deal of structure it was not easy to find places to duck down out of the current and lie in the sand to wait for the group and I was frequently kicking in place waiting for the group to catch up with me!. I was first back on the boat and was kind of tired out. It was the least enjoyable dive that I have done while in Cozumel. I asked the DM how fast the current was and he said maybe 3 knots at most. So for me I do not have an interest in doing the northern reefs. If everyone on the boat wanted to go there I would ask the DM once we got there how fast the current was and if it was strong I would sit it out. But thats just me.

Gaffer

 

[cenotist]

And just a little bit of math with quite extreme numbers for repetitive ow rec dives:
1st dive EAN32 @ 120 ft for 60 min (ppO2=1.47 ATA) = 50% CNS Tox
Surface interval for 60 min residual CNS Tox 31.5%
2nd dive EAN40 @ 83 ft for 90 min (ppO2=1.4 ATA) = 58.5%

TOTAL = 90% CNS Tox, what is well inside limits.

I believe most of us will NEVER dive this kind of extreme profiles, but even here is some margin for down currents. For example on the first dive: if it takes you down to the 145 ft (in the worst case scenario - in the end of your dive), you will have at least 3-4-5 minutes time at that MAXIMUM depth before you will reach limits 100% of toxicity. When you choose to dive Nitrox, you can (and should) do your math anyway, so do not make decision to skip Nitrox just based on your emotions. Put some numbers on the paper and then draw your conclusions based on them.

Another subject to add – I NEVER saw any of Nitrox divers (rec in Cozumel) analyse their tanks. When I shall jump from plain, I would like to check if my parachute is well packed. I know, that the Nitrox fillings in Cozumel are very up to date and safe and guys, who are filling the tanks are good professionals (I have a personal knowledge working with them), but you never know what mix-ups can happen elsewhere. And I would not want to discover those under the water.

PS! Never forget, that our bodies are all different and also resistance to the CNS toxicity. At the same time, tables have always room for some errors.

 

[Mike]

Yes, Mfinley, if the DM checks and says "the current is really quick, but diveable", I may very well tell him, "Thanks much, but I think I'll sit this one out," even if I'm not going to get a refund for a missed dive; the money is far less important to me than my own well-being. I'm old, fat, and not nearly in the shape I was 20 years ago when I started diving, but I hope to continue to enjoy diving for many more years. I'm not into diving for the adrenaline rush, but for the quiet solitude and relaxation of drifting over a beautiful reef and enjoying the wonder of the sealife, large and small. And I feel no need to prove to you, the DM, or anyone else, that I am "Man enough" to take a dive that's going to make me nervous or that I'm not going to enjoy. It's precisely the "macho", testosterone driven need to prove yourself to others or establish bragging rights that got those three unfortunate divers in Cozumel into so much trouble a week or so ago. So, Yes, I'll sit out a dive that I'm not comfortable making, and if that makes you think I'm less of a diver, go ahead and think that. I'll respect your right to have an opinion, if you'll respect my right to ignore it.

Thanks. Except for the part with your projections and insecurity about being less of a diver. Again, just a simple question with a simple answer, no need to defend yourself. People can actually simply ask a question here without it leading to anything more then it is.

I see nothing wrong with anybody that dives within their abilities, and I don't see anything in the words of last few posts by me that indicates otherwise.