"Accidental" deco with 1-day group, what to learn?

[fmerkel]

Wow.. fudging up on your Po2? I know that diving Nitrox with an air computer is just fine as long as you respect the MOD, but I have never heard of this approach. So your viper is tracking her dive as if you only had 74% N2. What would you do if your Uwatec went Tango-Uniform? I know.. you would probably be ok just adding another 10m to your safety stop. ...But are you sure?

So far, it's working fine. Set 'normally' it's annoying on multiple dive, multiple day trips. I've seen people hang theirs off the down line so it wouldn't freeze up, or sit out dives for the same reason. Unless you know a better way to tame the 'excessively' conservative nature of the Suunto (my opinion, not shared by everyone, but shared by many ) we'll keep doing it that way.

What if my UWATEC goes TU? Then I have my wife's 'messed with' Suunto, or my backup Favor. I'm comfortable with that. Having a computer croak on a dive is never fun but you just wander up and do a long safety stop.

 

[Caveeagle]

So far, it's working fine. Set 'normally' it's annoying on multiple dive, multiple day trips. I've seen people hang theirs off the down line so it wouldn't freeze up, or sit out dives for the same reason. Unless you know a better way to tame the 'excessively' conservative nature of the Suunto (my opinion, not shared by everyone, but shared by many ) we'll keep doing it that way.

What if my UWATEC goes TU? Then I have my wife's 'messed with' Suunto, or my backup Favor. I'm comfortable with that. Having a computer croak on a dive is never fun but you just wander up and do a long safety stop.

Not to beat a dead horse... but "so far, it's working fine" sounds like a one of those famous last words.. You may play out the math with several profiles and find out your 5%(point) reduction in calculated N2 creates a close match to your Uwatec, but I have always tried to respect Murphey's law. Not trying to be a jerk, but I don't think this a reliable method of reducing the conservative algorithm on the Vyper.

I would hate for somebody else to get into this habit and end up getting bent thinking they could just tweak a conservative computer to match their buddy's by dropping the N2 a point or two. I often dive two different computers just to see how they react to different dive profiles. I have noticed one computer might penalize me more on profile 'A' vs another on profile 'B'.

 

[dmaziuk]

...for short SIs, reverse profiles and/or omitted safety stops. For normal profiles with good SIs, it isn't particularly conservative. First dive of the day, square profile, the Suunto's NDL squares pretty well with the PADI RDP.

If you like some extra conservancy when other factors than max depth and bottom time indicate a somewhat less ideal profile, a Suunto is great for you. If you don't care about that extra padding under those conditions, not so much.

I wouldn't call 1 hour (I assume OP's "1h" stands for) SI "short". IIRC my PADI table, it takes you half way down the pressure groups. It'd be interesting to see what the 1st dive actually was and run it by the RDP: it may well be that 6 min NDL is within a couple of minutes of the table NDL and so not that conservative.

 

[kalleth]

Thanks everyone for the great feedback! It's been really interesting to read through so far.

But, I avoid situations where the dive guide is driving my dive profile. I either dive with a guide that I know in advance is very conservative; or I dive with my buddy, or if I am following a guide with no specific known buddy, then I do only shallow "swim around the reef" type dives.

In an ideal world, I'd do this, absolutely. But my diving generally takes me to places without buddies -- I'll take a day from a non-diving holiday and go diving leaving my friends to do their own things. If I limited myself to "swim around the reefs" i'd never see any cool wrecks!

Square things, sit in the kitchen, thats it; tables. Dive planning for the use of.

I can plan a dive on a table, no problem. They were still all the rage when I first qualified in 2000! But i'd rather use computers for multilevel, multi-stage dives as it reduces the chances of me messing up.

You had about 750 liters of air remaining, enough to bring a (calm) buddy to surface, so no big deal, especially since computers' NDL are very conservative.
Why don't you dive nitrox?

I don't dive nitrox yet because I'm still working out my technique on air, and I don't want to add to my task loading or potential points for me to mess up before I feel ready. Plus, so far, I've been able to access everywhere I need to. It's my next course, along with a rescue course.

When the DM told you to "wait there"..it sounds a little like you were sort of on your own in an over-head environment. Add to that, being uncomfortable with the dive plan and pushing NDL past your comfort zone.. (if I got that right)

Honestly, pushing NDL past 1 minute remaining exceeds my comfort zone. To credit the DM, he never "left me on my own" -- he was never more than ~4m away (a distance I was comfortable I could cover fast in an out-of-air situation) and I was comfortable with the plan as-briefed. But as-briefed didn't include any mention of accruing 20+ minutes of mandatory deco!

You should have given the 'Thumbs Up' signal and made it clear you wanted to end the dive. I agree that you were not in any real danger from deco, but it sounds like you were not comfortable.

I'm leaning towards agreeing. I've always been loth to give the "thumbs up" signal (i've only terminated a dive early once in 75 dives), but in this situation it was probably the right thing to do.

If there had been an issue with another diver.. Would you have been asset to help? ..Or an additional accident risk, if the whole thing went sideways?

Also, this sounds like the perfect dive profile for Nitrox. Especially when diving out as a single add-on diver. It would give you a lot more flexibility on types of dives you can do, with a better margin of safety.

I'd like to think I'd have been an asset, but I'm relatively inexperienced compared to the DM and most divers (although some holiday divers I've seen... I might as well be a DM next to!). Nitrox is my next course; above.

You were, frankly, put in a rather compromising position. It is one thing to accumulate 5 minutes of calculated 'deco' obligation at depth, which almost always clears on the ascent. But, you accumulated 20+ minutes, per your post, which didn't clear on the ascent. And, required you to stay down for ~25 minutes to clear the computer. Play out possible scenarios: What if you had not had enough gas? What if there had been an underwater emergency that thwarted the DMs plans to have everybody stay down and clear their computer?

One of the reasons I call myself a "conservative diver" is that I do play those scenarios out in my head a fair amount; I read Diver Down a few years ago and that's made me much more mindful of "what if" scenarios. That's one of the reasons I feel so uneasy about how this dive went.

As to what you might have done differently: it is a difficult call. Personally, I think you should have been more aggressive in ending the dive. But, that is not a criticism, just an observation, in hindsight (which is always wonderful). It is NOT within the domain of authority - or competence for that matter - for a dive guide to intentionally ignore a situation where a diver's computer is racking up a calculated deco obligation on a recreational dive. Simple as that.

I think you're right in that I should have been more aggressive in terminating the dive. I'll learn that for next time.

The take-away lesson: next time you are in a similar situation - preparing for a guided, deep dive: have a chat with the guide on the surface before the dive. Let them know that you are going to follow your computer if you run out of NDL. It is your dive, your computer, your health.

Absolutely; to make it even more embarrassing I've said similar to other buddies of mine when prebriefing on other dive trips. I should practice what I've preached.

So far, it's working fine. Set 'normally' it's annoying on multiple dive, multiple day trips. I've seen people hang theirs off the down line so it wouldn't freeze up, or sit out dives for the same reason. Unless you know a better way to tame the 'excessively' conservative nature of the Suunto (my opinion, not shared by everyone, but shared by many ) we'll keep doing it that way.

What if my UWATEC goes TU? Then I have my wife's 'messed with' Suunto, or my backup Favor. I'm comfortable with that. Having a computer croak on a dive is never fun but you just wander up and do a long safety stop.

This scares the bejeesus out of me, but I don't think I'm qualified or experienced enough to comment further, except to say that if you're going to ignore your computer, why dive with it in the first place?

I wouldn't call 1 hour (I assume OP's "1h" stands for) SI "short". IIRC my PADI table, it takes you half way down the pressure groups. It'd be interesting to see what the 1st dive actually was and run it by the RDP: it may well be that 6 min NDL is within a couple of minutes of the table NDL and so not that conservative.

I meant 1 hour. I don't have a comms cable for the computer or I'd happily share the profiles.

Thanks again, I'll keep checking back tomorrow for more info Now I have to figure out how to write the dive up in my logbook...

 

[dmaziuk]

I don't have a comms cable for the computer or I'd happily share the profiles.

Well the log screen should show you time and max depth (at least), so you can make a ballpark guesstimate of your pressure group after dive #1 and run it by 1 hour SI and see what NDL you'd get from the RDP.

 

[fmerkel]

This scares the bejeesus out of me, but I don't think I'm qualified or experienced enough to comment further, except to say that if you're going to ignore your computer, why dive with it in the first place?

I didn't recommend it. I just said that's what we are doing for now. We are not ignoring it, we are 'tweaking it' to suit our diving style. On some computers this is built in, not in the Suunto. Suunto knows best........

If you do a bunch of reading on comparing computers to one another you will come to the uncomfortable realization that ALL of them are approximations and they disagree with each other a lot, a whole lot when you go into mx dives/mx day scenarios. So, which one is right? The debate rages on.

I can tell you that we have become a world obsessed with dive computers, and we believe them no matter what they say. My UWATEC has 'conservative factors' from L0>L5. I dove it a bunch on L0, then thinking that things were less conservative as they went up to 5 I put it on L1. My wife still had her identical UWATEC at the time. We did a shore dive we've done dozens of times, so often that I really don't need a computer to do it, just an air and depth gauge. As we came in for our safety stop I had a surprising 5" of deco on a dive I usually would not have had any. My wife went in, I stayed and did my deco, mostly to not freeze up the computer, but also because the damn thing was telling me I had to, while my experience told me it was ridiculous.People are that way.

BTW, the main reason we got it was because we were tired to death of other brands (many) dying not long past warranty and crappy support from the lot of them. This seems typical of the industry. Suunto seemed to have a better reliability reputation. Had we known how conservative it was we probably would not have gotten it. The manual sucks toads too.
Some things have to be learned the hard way.

 

[Diver0001]

There is no such thing as "accidental deco".

There is, however, a thing called "ignoring your computer".

The OP's post is just one big... long... excuse for why he ignored his computer. There is absolutely no excuse for that. The problem he had was completely avoidable and he deserved a firm slap to the face. There was literally nothing happening here beside user error.

R..

 

[fmerkel]

There is absolutely no excuse for that. The problem he had was completely avoidable and he deserved a firm slap to the face. There was literally nothing happening here beside user error.
R..

Negative input tends to create negative results. The OP is making an honest attempt to learn from a situation loaded with information he did not quite understand. It is a very good opportunity. We don't learn nearly as much from our successes as our 'so called' mistakes. When someone is slapped down for trying what they learn is that they should slap people down for trying.

 

[Caveeagle]

I didn't recommend it. I just said that's what we are doing for now. We are not ignoring it, we are 'tweaking it' to suit our diving style. On some computers this is built in, not in the Suunto. Suunto knows best........

I am not aware of ANY dive computer that reduces the N2 in the deco algorithm as a method to created a less conservative dive profile. There are many other variables that go into the calculation. Mathmatical models that predict rates your body tissue groups will absorb and off-gas... for example.

...I can tell you that we have become a world obsessed with dive computers, and we believe them no matter what they say.

Gargage in, Garbage out. Until you justify the reasoning behind the 5%point adjustment in N2, I respectfully suggest you are proving the "Garbage in" side of that old adage.

My UWATEC has 'conservative factors' from L0>L5.

Yes, do you know exactly what variables the Uwatec tweaks to modify the profile? I bet its NOT N2.

..Suunto seemed to have a better reliability reputation. Had we known how conservative it was we probably would not have gotten it. The manual sucks toads too.

Sell it to someone who wants a more conservative unit..... and get another Uwatec if that's what you like. I got my last Aladin Pro for $10 and swapped in a $8 battery. Works just find now.

Some things have to be learned the hard way.

...Very True

 

[kalleth]

There is no such thing as "accidental deco".

There is, however, a thing called "ignoring your computer".

The OP's post is just one big... long... excuse for why he ignored his computer. There is absolutely no excuse for that. The problem he had was completely avoidable and he deserved a firm slap to the face. There was literally nothing happening here beside user error.

R..

Although I agree in general, I think you're missing a few points here. There's a reason I put "Accidental" in scare quotes.

First, I was diving with a group who were all more experienced than me -- quite a bit more, in fact. Second, I was diving with an Instructor, acting as a dive guide, who when I pointed out my computer (having not ignored it, and having communicated it to him frequently and in a timely manner) *told me* to stay put.

I made several mistakes here -- one being that I didn't then tell him "no, we're terminating the dive", but it's intimidating to do that to an instructor and a group of people who are all more qualified than you. That's what I'm trying to work past -- and what I'm asking for advice on.