Dealing with Downcurrents

[Mike]

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

That's the nature of the north sites, they are what they are and there are issues with current and bottom time that can make them basically along for the ride. I've been on all the variations, for certain when you hit them with a slower current the dives are quite different and enjoyable in a different way, however even when the current is fast if you're in a matched group, you'll all be in the same 'boat' and ride the current as a group so it's just sit back and watch the show go by, safety stop and back in the boat without incident. I've experience dives that deviate from this when OPs take miss-matched groups, groups with half on nitrox half on air, ect... and the group gets split up at different depths and when that happens sometimes 10 or 20 feet in depth can make a great difference in what current you will experience. I had one dive like that on San Juan I believe with 1 person on nitrox who was hugging the reef more and actually stopped to watch an eagle ray, leaving 6 others to fin misserably for what seemed like an eternity, so as not to be swept down current until she unglued herself from her perch. Was not fun.

 

[azscubadude]

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

I'm another one of those old guys (64) and we dove Punta Tunich just a week or so ago (8/31 to be exact) and the current was ripping (and I mean really ripping). We were traveling faster than the video someone posted a link to. Had to be the fastest current I've ever been in while diving Cozumel. It was an amazing ride and to be honest.. a lot of fun. We had a small group of experienced divers with excellent buoyancy that stuck together so not to split up the group. All we could talk about when we got back on the boat was how amazingly fast and far we had traveled. I think we saw more critters on that dive than on any other dive of the week (but you couldn't blink or you would have missed them).

 

[stevep4444]

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.

Interesting. I mixed in some nitrox dives when I was in Cozumel recently. I got the impression from the staff that the nitrox tanks were pretty well treated like tanks with air from a perspective of just load them on the boat and hook them up to the reg.No one else was diving nitrox so I did not witness how others handled it. I insisted on testing every tank myself and they were all within 1% of requested mix. It just comes down to the fact that you are responsible for your own safety,whether it is nitrox,diving dives to your ability or comfort level,deco,off gasing,air supply,etc.
My hat goes off to the divers that thumb the dive when necessary rather than risk their safety and enjoyment. The price for being macho can be very large.

 

[cvchief]

We almost always analyze the nitrox. I have had a tank off my a few percent, but not much. The other important thing is after you set up and test, tear that orange label off. It comes off in the water and floats away.

 

[Prop Joe]

Interesting. I mixed in some nitrox dives when I was in Cozumel recently. I got the impression from the staff that the nitrox tanks were pretty well treated like tanks with air from a perspective of just load them on the boat and hook them up to the reg.No one else was diving nitrox so I did not witness how others handled it. I insisted on testing every tank myself and they were all within 1% of requested mix. It just comes down to the fact that you are responsible for your own safety,whether it is nitrox,diving dives to your ability or comfort level,deco,off gasing,air supply,etc.
My hat goes off to the divers that thumb the dive when necessary rather than risk their safety and enjoyment. The price for being macho can be very large.

We (my dive buddy and I) have our own analyser just for this reason. Why on earth would you subject youself to breathing an unknown gas???
Current is a personal decision and if not comfortable, by all means either stay on shore or on the boat. I respect that. I've seen people make those decisions and not one diver should ever push people to perform dives they do not want to perform...
This diving thing is supposed to be fun, your fun, not somebody else's fun. Plan accordingly and don't budge from your decision.

We have had some great boats that everyone was on NITROX, great with air consumption and we dove deep sites from Punta Sur Sur all the way to the ripping currents up north (with the funky up/down washing machine currents), the wild East side and everything in between. I've also had great trips with my 73 year young aviation mentor that made me just as happy to see him enjoying diving. Fun, fun, fun!!! Tell the operation what you want to do before you get there and they should be able to grant your requests, weather/current conditions permitting. Be safe!

 

[cenotist]

We almost always analyze the nitrox. I have had a tank off my a few percent, but not much. The other important thing is after you set up and test, tear that orange label off. It comes off in the water and floats away.

Exactly my point. As I said, I do not question the quality of Cozumel fills (if we get 1-2 percent different reading on the gas, it is probably the bad calibration of our tools ) another thing is how much do you trust that this good fill ends up with you in a dive. Do we pin our fight to this orange/green microscopic label on the tank, what might be there from the last dive or transferred from the handling of tanks or … do we even read what is written on this label? Probably people from this forum, yes, but what about our friends on a dives?

I am not trying to be more catholic than the Pope, but it is healthy to put some macgyver on the tank and write our own testing results on it. Among other reasons it is good information for chamber doctors in the case of accident. I do not know how it is in English, but in Estonian we have a saying that if you want to avoid rain, take your umbrella with you.

 

[cvchief]

I do not know how it is in English, but in Estonian we have a saying that if you want to avoid rain, take your umbrella with you.

Well that works pretty well in English too. but I like getting wet and never take an umbrella diving. I get a kick out of our nitrox dive briefing. Every time it is "Do not go deeper than 100 feet on that Nitrox" and then I say "Uh, actually the computer says 98 feet" then she says "like I said no one will go deeper than 98 feet." Love the schtick.... (We don't get close to 98 feet, its just the standard briefing before anyone starts....)

 

[Zman96]

I would never splash down on Nitrox without seeing the analyzer for myself. I use BlueXT and they always have one on the boat to use if you do not have your own, and their DM's always checks the tanks too even if the person on the boat didn't ask.

 

[DandyDon]

Any Op offering Nitrox should also offer the use of an analyzer. I carry my own tho, just in case.

I have seen enough confusion on tanks to wonder if I should check all tanks for O2 levels. It wouldn't take long with my Analox portable units: 5 seconds on the Oxygen analyzer, 5 seconds on the CO unit - ok, good to go.