Question about deco stops when diving with air.

[impulse]

The OP is also a pretty new diver. He's got a lot of lessons yet to learn. He got one from the reported dive, but what worries me is that it was the wrong one. Instead of learning the lesson that he needs to monitor his status more diligently and do a bit more pre-thinking about his dive, he got the lesson that he needs to study decompression theory. Studying theory isn't a BAD thing (I wish more people would do it) but the real lesson is to be more careful. I hope he's heard that one from us.

I will keep this advice in my mind. I will pre-think about the dive next time. Thanks for the advice.

 

[impulse]

If you can't adhere to a NDL limit, you'll just end up breaking the deco plan once you get the training. Irresponsibility isn't fixed by training. I would just continue to dive unsafe at the OW level rather than blowing money on a deco course with your maturity level.

Well, maybe I got a different kind of logic. I never thought about breaking the deco plan. I never thought about that because in that case you plan the dive and you have some designated bottom time and a designated deco depth and time. You cannot forget a plan. I want to learn the decompression theory, stay next to my buddy and try to watch his status with my limited knowladge about diving and escape from a deco and ascend to a more desirable depth and you call that irresponsibility. Maybe I must really never stayed with my buddy and let him hurt because of some damage from a possible decompression sickness. Because some divers I see do that. They let their buddy stay deeper without a computer. Because they are not aware that a 7 fsw difference would be the thin line between exceeding or not exceeding the no deco limitis. But I am aware. Hmmm, but I forogt, I am irresponsible. Or maybe I am over responsible and I triend to think about many details below 125 fsw as possibly being narc'd. And one other detail is, that buddy of mine (who I never met before that diving) has an AOW certificate. He is very resposible! Really! Maybe I am still narc'd?

 

[impulse]

That is exactly the wrong instinct, and the wrong message to take away from what everyone has posted. Although it is a common response of newer divers to the problem of diving deeper/longer to go out and get more gas.

A pony bottle introduces another valve, another SPG, another tank neck o-ring to bubble and leak, another regulator to make sure is deployable and breathable underwater. And if any of those things go wrong, it is a worse than useless piece of gear because it just introduces complacency about your ability to dive deeper/longer.

What you need is skills:

- ability to hold buoyancy control and trim at your stop without a reference

- ability to donate gas safely and efficiently every time

- ability to manage your gas

- ability to plan and execute your dives

You should be able to check off all those skills before you start bumping up against the NDLs. Right now you should be leaving the bottom with a lot of NDL padding available to you so that you don't incur any real decompression.

Later, you will probably have a sufficiently low SAC rate due to comfort in the water that being aggressive on a dive by a few minutes and incurring a few minutes of mandatory decompression that you can do aggressive NDL dives without additional gas reserves.

So, you've got it completely backwards. Don't buy gear and also don't worry about learning about decompression. You need to go out and become a better diver through experience and more training. You need to focus on your fundamental skills, and not decompression -- GUE fundamentals, UTD essentials and NAUI intro to tech, would be courses that I'd encourage you to look into -- you don't need a deco procedures course right now.

Ok thanks for this great advice. I never thought about all those problems that my arose from carrying a small extra tank. As you know that's because of my limited knowladge.

During our safety stops, all the divers hold the rope or the chain that's comming down from the boat. Maybe not holding the rope and trying to control bouyancy and triming it at the safety stop depth aroud 16fsw would be a good way to excercise about holding bouyancy control.

And one questions is, I bought an apeks at20 regulator and an apeks at20 octopus. After I started to use this new set, my gas consumptions increased a little bit. Before that I was using the regs that the diving school or the boat that we go diving with provides and my gas consuption was lower. Why would this happen?

 

[impulse]

Impulse, let me ask you a question:

You seem very worried about suddenly and unpreparedly running out of "no deco time".

There is another limited recource in diving with a much harder and unforgiving limit - your gas supply.

If you don't have the awareness to complete a dive and respect/stay within your no decompression limits, what makes you think you can stay within the limits of your gas reserves?

After all both require esentially the same planning, execution, and awareness skills except that a couple of minutes of omitted deco will likely cause nothing but a good nap while running out of gas could kill you if your buddy is off photographing the pretty fish when it happens.

For some reason I check my the gas reserve frequently. Maybe that is a survival thing. But from now on I will be cheking the computer as frequent as I check the gas reserve.

 

[impulse]

You have to ask what the pony is for, though.

Is the pony being used to provide with redundancy in case of an equipment failure?

or

Is the pony being used to provide an additional gas supply because someone doesn't know how much gas they actually need to do a given dive.

If you go and find my reply about that, you will see that I was thinking a pony as a deco gas like nitrox. But for somereason everyone say that it's not safe to carry a spare gas tank. Well, not a spare gas tank, a deco gas tank. These are different. I meant to use that in the event of a compulsory deco stop but lamont changed my mind. It would cause added problems as lamont points out.

 

[Bubbletrubble]

And one questions is, I bought an apeks at20 regulator and an apeks at20 octopus. After I started to use this new set, my gas consumptions increased a little bit. Before that I was using the regs that the diving school or the boat that we go diving with provides and my gas consuption was lower. Why would this happen?

@impulse: It's certainly possible that your Apeks AT20 reg setup is tuned differently than the ones in the rental fleet. This might make it easier to initiate gas flow (lower cracking pressure) and easier to maintain sustained flow (Venturi effect). This could set up a situation in which the reg is delivering a little more gas than necessary (or at least more gas than you were getting from the rental reg).

Personally, I like my reg to be tuned on the edge of freeflow to decrease work of breathing at depth...but I also have an inhalation adjustment knob that allows me to detune the reg on-the-spot and protect against unintentional freeflow. Tuning a reg successfully has a lot to do with finding a happy medium between too much breathing resistance and freeflow. Compared to personally owned regs, rental regs are usually tuned farther away from freeflow.

Hope this info helps...

 

[TSandM]

impulse, it really isn't necessary to carry a deco gas just "in case" of exceeding your NDLs. As people have said, if you begin an ascent, your computer may well clear your deco obligation before you get to the shallows, and if not, you can do the deco on the gas you have in your tank, assuming you have enough of it (which is the big issue). The reason people use decompression gases in technical diving is because the time they would have to spend decompressing rapidly becomes unmanageably long, and is significantly shortened by using gases with less nitrogen in them. But for the very brief hangs you'd need for an inadvertent violation of the NDLs, backgas will do just fine.

As I said before, learning more about decompression theory is not a bad thing. But staged decompression diving has a lot of facets to it that aren't immediately obvious, so it isn't something to undertaken lightly.

 

[impulse]

impulse, it really isn't necessary to carry a deco gas just "in case" of exceeding your NDLs. As people have said, if you begin an ascent, your computer may well clear your deco obligation before you get to the shallows, and if not, you can do the deco on the gas you have in your tank, assuming you have enough of it (which is the big issue). The reason people use decompression gases in technical diving is because the time they would have to spend decompressing rapidly becomes unmanageably long, and is significantly shortened by using gases with less nitrogen in them. But for the very brief hangs you'd need for an inadvertent violation of the NDLs, backgas will do just fine.

As I said before, learning more about decompression theory is not a bad thing. But staged decompression diving has a lot of facets to it that aren't immediately obvious, so it isn't something to undertaken lightly.

I didn't know that there all those factors that play role when decompression is the subject. Ignorance can be cleared by seeking advice. Mines did. Thank you.

 

[Matt S.]

And one questions is, I bought an apeks at20 regulator and an apeks at20 octopus. After I started to use this new set, my gas consumptions increased a little bit. Before that I was using the regs that the diving school or the boat that we go diving with provides and my gas consuption was lower. Why would this happen?

Your gear could be a factor, but your air consumption from one dive to another can change because of a lot of things. . Maybe you were warmer on one dive because your pre-dive routine was a little different one day. Or maybe you were just been more "in the zone" sometimes. A longer surface swim could make you more tired at the beginning of a a dive, so you breathe more heavily... Those kinds of things can make small but noticeable differences in your air consumption.

 

[dumpsterDiver]

Impulse, you need to read the dive computer manual and understand it. Then take all that crap about how dangerous a pony bottle is and pretty much throw it out the window.

Then, take the idea of carrying a deco bottle (which I can only assume you intend to fill with an oxygen rich mixture) and forget about it, because that piece of equipment (using the wrong gas at depth) has a much higher probablity of killing you than any safety it provides, especially for a planned no-deco dive.