Beep beep going into decom :-( or :-)

[DA Aquamaster]

Peo once bubbled...
Put another way, for a given dive, you will have shorter bottom times since you loose half your gas in case of a problem, and thus will need to cut the dive shorter to be able to get out.

You make some good points and it is critical to manage your air with independent doubles so as to have enough air in each tank to finish the dive safely at any point where a failur could occur. But this just requires that you plan the dive and dive the plan.

On a normal dive where nothing fails you are not at any disadvantage in terms of air capacity compared to a set of doubles with an isolator manifold as you still need to keep 1/3 in reserve with either configuration.

Also, if you have a problem with a conventional set of doubles and an isolator manifold, you still should abort the dive immediately. You lose the benefits of redunancy if you push on after a failure and are really taking an unacceptable risk if you continue. Having a failure and continuing the dive should not be part of the plan.

But you are entirely correct, an independent doubles configuration does have it's limitations and you need to be aware of them and plan accordingly, just like with any other configuration.

 

[Peo]

DA Aquamaster once bubbled...


You make some good points and it is critical to manage your air with independent doubles so as to have enough air in each tank to finish the dive safely at any point where a failur could occur. But this just requires that you plan the dive and dive the plan.

On a normal dive where nothing fails you are not at any disadvantage in terms of air capacity compared to a set of doubles with an isolator manifold as you still need to keep 1/3 in reserve with either configuration.

Also, if you have a problem with a conventional set of doubles and an isolator manifold, you still should abort the dive immediately. You lose the benefits of redunancy if you push on after a failure and are really taking an unacceptable risk if you continue. Having a failure and continuing the dive should not be part of the plan.

Yes, I would abort the dive if I broke one of my first stages. You can argue both ways if one of the first stages froze -- personally I'd abort even if I could get it to work again by shutting it down and turning it on again after a couple of minutes.

But the difference here is the situation you are in once that emergency that caused you to shut down has been dealt with. When you shut down one of your first stages you have lost half your remaining gas supply (given "proper" gas management). With a manifold, you have the same amount of gas available, for both you and your buddy. You aren't pushing the limits on your own gas supply, and you can actually help your buddy by buddy breathing should something more happen.

Anyways, better not turn this into a manifold or no manifold war -- I just want to point out that it's not a 100% accurate description that diving independent doubles utilizes a simpler technical system, and therefore is safer.

 

[Falcon99]

You know, I've seen some considerable 'flaming', or at least the closest I've seen regarding going into decompression dives before 'properly trained'. It struck a chord with me in a strange light as a newby diver and recently experiencing my first trip to Cozumel.

Before I go into the Cozumel experience, I need to give a quick peice of backbround. I'm a former AF aviator, graduate of Navy pilot training, and VERY attached to the concept of detailed training progression. Contrary to what most people saw in Top Gun, the military aviation community (for the most part) is VERY rigorous and training-disciplined.

So, not knowing any other method, I was EXCEPTIONALLY careful with scuba diving. After basic OW, I read every book I could get my hands on regarding advanced diving. I basically memorized my computer owner's book, and so on...

In a nutshell, our dives in Cozumel were about 45 minutes at 40-60 feet, with about an hour SI. During our first dive, my computer went dangerously close to decompression mode. On the Atmos ai, I was one detent away from the red zone - decompression. The second dive brought me close to the same thing. being the inquizitive person I am, I asked my partner and the DM what the deal was and for 'FYI' stated that I might have to terminate a dive early if my computer got too close for my comfort.

The response from my dive partner, and the DM, was basically a stupid look, along with comments like 'your dive computer is too conservative' or 'don't worry about it, your being paranoid' yadda, yadda.

In short, I was told I was being a wet blanket and a wimp for not 'pushing the limit' I was disgusted. Looking back at the PADI tables and following recreational rules by the letter, we busted the tables on every single two-tank dive. Again, I mention this to my partner and get a third degree during lunch...

My point here is that there is a MAJOR hypocracy going on and in my opinion after what I have seen, you guys pointing fingers are just as guilty as the rest. If the standards are wrong, then correct them. Otherwise, shut up and follow the rules. As an aviator, you didn't dare call someone a wimp for pushing the envelope because people get killed (remember the B-52 incident?).

Regardless, I intend to ALWAYS stay within bounds, even if is pisses someone off because their dive ran shorter than they wanted. Sorry, but until I see you guys following the rules out on the boat, the flames on thgis board are hard to believe....

Jim

 

[Jonathan]

I would definitely say that your buddy and DM on Coz were in the wrong. Yes you computer may be more conservative and that could be a good reason for buying it but at the end of the day anybody can call any dive at any time without repercussion.

Anyone that gives you stick on that should be left to play their own game of roulette....

Anyone diving with a computer on a holiday with multiple dives in a day will blow any tables. These are designed for square profiles and who dives square profiles? Mainly technical divers....

Then we get into the whole debate of computers good/ computers bad and there are many threads out there you can follow that up on.

Jonathan

 

[BigJetDriver]

Good advice there, Jonathan! As most good texts on diving problems mention, peer ego pressure (as was described by Falcon) can push divers into doing things that they should not do! He, at least, had the training and mental fortitude to resist it!

 

[Genesis]

So what if you get pushed into deco?

As long as you plan the dive so you have the gas to complete it (including necessary redundancy if required!), and either the computer for it or the tables to specify it, so what?

All dives are decompression dives. Its just that we do the "decompression" on the surface, during our SI, when we dive as "NDL divers."

All that happens when you exceed those limits is that the ceiling comes down from 0' (the surface) towards your present position.

Provided you have the gas (guaranteed, not "I think so", or "if anything goes wrong I'm screwed") then deco is not a big deal. You're already doing it as a diver - you just need to do some of it while still in the water.

 

[BigJetDriver]

Genesis once bubbled...
So what if you get pushed into deco?

I don't disagree with anything you said AFTER that first sentence. The point you missed is that Falcon, despite some really amazing life experience in other areas, is a fairly new diver.

He obviously doesn't want to approach that margin just yet. After more dive experience and some good training, he will, no doubt, understand the subject better and feel more comfortable with pushing the edge of the envelope himself!

 

[Genesis]

and quite honestly I agree with his general principle.

But you can always be more conservative on your ascent than the computer (or tables) require. I do this all the time, and so do lots of other people. Spending three to five minutes at 15' is part of that - most computers "suggest" it, but don't require it.

We still do it, and that's a deco stop - is it not?

On my dives I typically do at least one and sometimes more than one "un-called-for" stops. For dives over 40-50' or so I stop for one minute either at each atmosphere or at the "halfway point" on the way up, and also typically start my "safety stop" at just above 20' (where my computer starts "counting" it) and from there do a very slow ascent profile, typically with 5 minutes from 20-15', and then a very slow final ascent from there (3-5 fpm from there to the surface is typical)

All this is added conservatism over what the computer demands of me, but that's a choice - and it can be with him too.

 

[DA Aquamaster]

A large part of my comfort level when deco diving is having a more than adequate redundant air supply and knowing that I will be able to do the deco required even if something fails.

I also agree that all dives are deco dives and that planned deco is not a big deal with proper planning and equipment.

I also agree that you can add saftey stops or additional time onto the required deco stops and that this is a good idea. I normally add a minute or two to the 30' and 20' stops and 3-5 minutes to the 10 ft stop. I also do a 1 min deep stop at half max depth and will often finish deep dives (deco or otherwise) with a prolonged swim in the 30 ft range burning a few hundred psi and adding what is essentially a very long saftey stop while looking at the fish.

And I find it odd that many divers who would not consider deco as it is not safe or within the rules will often use ascent rates well in excess of 30 fpm or even 60 fpm and think nothing of it because they have always gotten away with it in the past. In essence though, exceeding a maximum ascent rate is basically the same as blowing off a short deco stop and sooner or later it will bite you.

 

[blackice]

JeffG once bubbled...

All the advice you need?: You don't need advice..you are already doing deco dives before you are trained for it. Hurray for you...Transcend your training....

Why did you bring the subject up, and now want to close it?

Did you do something bad?

JeffG,
Yes I think I had enough advice from the board, the main leasson learnt is that NDL are there for a reason and to go beyond is risking the safety of myself, my buddy and others.

But I also realised that it happens, it shouldn't but it does, and it's how you plan / reliase what to do that matters.

I didn't go into deco with out knowing, I was very aware. I went to '0' then waited to see what happened... it said I had 4 mins deco at less than 3meters, so we slowly went up to 5m then staqrted deco for 4mins + 2 more to be safer.

I realise that this is risky and will not do it again, but I think the reason I asked aobut it was that it had never happened before and I was wondering if it had happened to others.

I may have lead you to believe that I was intending to do this often and was not aware of the computer or the limit, but this is not true.

I was saying that we could close the topic as I personal had got the answers I was seeking, but others may have question to continue so the topic continues.....

Have a good day,