A Game: WHAT WOULD YOU DO?

[SeaJayInSC]

You're on your third dive of the day and near the end of your dive. Depth is 81' in the open ocean on a not-so-well-known wreck. You've been completely tantillized by the marine life and massiveness of the wreck.

You look down at your dive computer and notice that it says that you've got 1 minute of NDL left, even though you've still got 2,000 psi or so.

What would you do?

 

[reefnetworth]

being you 3rd dive?
check my gear to insure its proprly in order, something doesnt sound correct in your readings.

 

[tgreene]

If you dive the PLAN rather than the COMPUTER, then you will know where you stand at all times based solely upon your timer and SPG, in case the computer has failed.

See, I can learn things!

 

[SeaJayInSC]

You're right, Tim...

If this diver was diving the plan, then he shouldn't be surprised that his computer is telling him that he's got one minute.

Reefnetworth, a scenario like this can commonly happen when surface intervals are short, and repetitive dives load up the body. The computer knows this, and so it shortens available bottom time, even though the diver's just gotten a fresh tank and has only been underwater for a few minutes.

...So your gear is fine. Still reading 1 minute, but about to show you 0 minutes.

What would you do?

In case you guys are wondering, there's not really a right answer - I just want to throw this out there to get divers thinking about scenarios. As this thread progresses, I'll give you more and more difficult situations to deal with, and we can all discuss them.

...Which should end up teaching us all a lot about diving, even if you're stuck on surface interval.

Okay, gear's fine. 2000 psi - 1 minute to NDL, according to your computer.

What would you do?

 

[tgreene]

<a href=showthread.php?s=&postid=15021377#post15021377 target=_blank>Originally posted</a> by SeaJayInSC
Okay, gear's fine. 2000 psi - 1 minute to NDL, according to your computer.

What would you do?

That's going to depend quite a lot upon the previous 2 dives and SI's and what your current RNT is. Without those facts and figures, I would have to default to the "Rule of 120" that you taught me a few months back, but being the 3rd dive that rule would have scaled back to something more like 90, so with allowing for a safe ascent based upon "90" being the 3rd dive, and you're at 81', I would guesstimate that you actually have a safety zone of 6 more minutes BT plus your 3 minute safety stop. Again, I'm basing this solely upon the ASSUMPTION that I have properly understood what you have been trying to teach me...

1st dive of the day, use the Rule of 120 - this is an old Navy Diver addage: Depth + time = 120. For example, at 80 feet, you've got 40 minutes. At 100 feet, you've got 20 minutes. At 60 feet, you've got 60 minutes. Get it? Now go compare that to your tables or wheel - you'll see that the numbers are off just a touch, but by surprisingly little. That's because PADI added in a "safety margin" of their own. They were simply being conservative. The problem is that if you add in your own conservatism (a good idea, right?) now you're so super-conservative that you're worried about nothing - or cutting your dive short, which in my case means money, too. If you graph the two out (time on X axis and depth on Y axis), you'll also find out that the "Rule of 120" is a straight line, whereas the PADI tables are actually curved a little - making PADI's tables more conservative in the middle, but more liberal at the ends. I'm not telling you that you shouldn't practice the PADI tables and instead use the Rule of 120... I'm telling you that there's a close correlation, and if you see how the two of them look similar, you'll be much more familiar with what you can and can't do when it comes to your NDLs (which aren't a limit anyway - you'll learn that later and wonder why you even considered a dive computer that blinked a limit at you when there's not really a limit there).

For example, now that you're thinking about the Rule of 120, when you hear someone tell you that they dove to 110 feet and stayed there for 30 minutes, you'll know that they're pulling your leg unless they were doing staged deco on their asent. When someone tells you that they dove to 60 minutes and were past their NDL in 22 minutes, you'll know that something's really wrong with the story. And when you're at 90 feet and your computer floods, you'll know that you've got about 30 minutes to get out of there before things really get out of hand.

Basing the overall stats upon the computer is quite honestly going to depend upon which brand of computer you're using because the algorithms are not all created equal. Some maps are are much more conservative and "restrictive" than others and they are well know to throw in penalties... My Gekko is best known for this, which is one of the reason that I stated the other day that I did the computers 5 minute hang time, rather than the 3 that I actually needed for the dive.

-Tim

 

[tgreene]

..

 

[SeaJayInSC]

Based on the above information that I gave you, the correct thing for you to do is to ascend, unless you've planned a staged decompression dive.

Basically, if the plan is to stay within your NDLs (according to your computer), then it's time to go. In fact, technically, you're on "the ragged edge" of your dive, and have probably overstayed your welcome. One minute isn't much.

Interestingly - and this is the point of this scenario - as you ascend, your computer will ADD time to your NDL. For example, as you pass 60 feet, your computer may then tell you that you've got 4 minutes of NDL, then 6 as you pass 40... And so on. Most systems will then tell you to "STOP" at 10 for one minute as a "safety stop," which, interestingly, negates the whole point of "no-decompression diving" (staying within your NDLs). If you have to stop, then that's, by definition, staged decompression diving.

...Which sorta makes you wonder.

...Which is the point of this thread.

Basing the overall stats upon the computer is quite honestly going to depend upon which brand of computer you're using because the algorithms are not all created equal.

That, too, is a great point, Tim. Okay, new scenario:

You're diving at 75' of saltwater over a very pretty reef. You're deep because you're looking for lobster on this dive, and so you're right on the bottom and looking in every hole.

Your buddy flashes his light at you and points to his computer. He's got 3 minutes of NDL left. You notice that he's also sitting at just a tick over 1000 psi.

You look at your gauges and see that you've got 1200, with 8 minutes left, because your computer is a different brand.

What would you do?

 

[SeaJayInSC]

By the way, Tim - the Rule of 120/Rule of 110 only applies if there's been at least a 1-hour surface interval between dives.

120 for the first dive, assuming no other diving in the past 24 hours... 110 for subsequent dives, assuming a 1-hour surface interval between dives.

...And again, I'll reiterate that this does not follow PADI's tables to the letter, but it's awfully close, especially in the middle - so once again, these "rules" are only good for an estimate - and what they estimate is the US Navy dive tables, not PADI's or NAUI's.

Do the longhand - use the tables and see how they compare to the PADI tables for further understanding.

The Rules of 110/120 are not designed to be an "end all" to understanding your NDLs.

...But then, neither is your computer.

Taken one step further, PADI's tables, NAUI's tables, the "wheel," or even the new RDP computer shouldn't be considered the "end all" for NDL diving, either. The point is to understand all of them, and understand how they all differ.

Knowing and understanding this will create in you an inherent and significant comprehension of your NDLs... Which will make you a better diver.

Then, when your computer fails or you blow your tables or the fit hits the shan, you'll better comprehend your options.

Interestingly, the circles I run in have a fundamental belief that there is no such thing as an "NDL" because there's no such thing as "no decompression diving." To them, EVERY dive is a decompression dive - it's simply a matter of the proper method of exiting the water.

In some cases, you can ascend at 60 ft/minute. In some cases, you've got to do it at 30 ft/minute. In other cases you can do it at 30 ft/minute when you're deep, but you have to go slower when you get shallower - so stopping at 40, then 30, then 20, then 10... What some would call "staged decompression diving" - and others call "tech diving" - is required.

...Which, if you think about it, really blurs the line between "rec" and "tech" diving.

...Which is already blurry anyway, since your "rec" computer is telling you to stop at 10 feet.

Okay, enough food for thought. Above scenario: What would you do?

 

[tankdvr]

Get my nitrox cert, then do the dives with the appropriate mix (32% would be a nice safe mix if you're not going to go deeper than 110' for the day).......

In the scenario you posed, the only safe thing to do would be to get your buddies attention (and hopefully he's realized that he's in the same boat you are) and get back to your anchor line. Then slowly begin your ascent, as you go up your comp should be granting you more bottom time. If there's a reef around 40' or so, you're set. You could probably burn off the rest of your air there. If not, just finish your ascent or hang out on the line and stare into the blue. If you're lucky you might see something cool.

 

[snorvich]

I would go up but I would not be in that circumstance as I would have planned the dive. Remember, that computers are based on tables with AVERAGE results. You could still be in the tail end of the curve with a different risk level than you know. You could be older, heavier, hung over, etc. NEVER push your computer.

 

[Grunt]

I'd ascend regardless of psi in the tank. Not worth pushing the limits and possibly ending my day in a hyperbaric chamber (or in transit to one).

Proper planning and observation of your equipment will help to deter this situation from happening. Most computers have audible alarms at greater times then 1 min also.

I would also evaulate the company your diving with and if your happy diving with them.

 

[SeaJayInSC]

Yep, you're all spot-on correct.

The point is, if you're going to buddy-dive, the dive is only going to last as long as the weakest link in the dive. I also wanted to show an example of what Tim was mentioning about different algorithms showing different NDLs - in some cases radically different.

In other words, different computers - even the same computer, but different years of manufacture - can show radically different data. I have known some people to wear multiple computers - say, a Genesis and a Suunto, side-by-side on the same wrist - and get radically different data from each. The problem, of course, becomes, "which one do you trust?"

The answer, of course, is neither of them - you trust your plan, which should have been established already, above the water, when you had the chance to discuss it with your buddy and logically consider it against tables, the "wheel," the RDP computer, the Rule of 120/110, and the like... All when you're dry and can focus without distraction or the haze that comes with being narced.

New scenario:

You're diving on a kelp bed and enjoying the underwater "forest" of plants and marine life. Things are great, and you're toward the end of your dive.

Having chased several interesting-looking fish, you've considered that unlike your plan, you have not done a good job of maintaining depth... Your "profile" has been a little up-and down. As the needle on your pressure guage dips below 800 psi, you figure it's time to head topside.

Ascending from 50' or so (not your deepest point in the dive), your computer flashes at you to "STOP" at 20'. This is surprising to you, and a little concerning - this wasn't part of the plan. Nearing 21' (and ascending), you notice that your pressure guage is sitting at about 600 psi. If you stop at 20' (as you approach it tells you that you've got a 3-minute stop there - and you know from past experience that it's also going to tell you to stop at 10' for 5 minutes - then you might not have enough gas to do this.

You motion to your buddy to show you his guages. His needle is sitting just under 500 psi. This is upsetting, 'cause the Divemaster aboard the boat said to "be back on the boat with 500 psi, and you aren't going to make it.

Do you have to stop? Should you stop? This wasn't part of the plan...

What would you do?

 

[tgreene]

I'm gonna go way out on a limb here and say that you should very slowly surface while sharing air w/ your buddy in the hopes that you'll both surface with as close to 500psi as possible, as well as being off-gassed enough to no longer need the 20' and 10' stops.

-Tim

 

[snorvich]

I disagree. The divemasters admonition, while desirable, is no longer safely possible. I would do the required stops as closely as possible to my buddy while breathing very deeply and slowly. You DO have enough gas to make those stops as your utilization rate will be much lower at shallow depths. But I would have monitored my air and no decompression time long before that time (I do it very frequently by habit) and would not have run into that circumstance.

 

[Grunt]

I agree with Steve!

My buddy (usually my wife) and I would continue with our safety stop regardless what the divemaster says about psi. It's easy enough to tell them that you used the remaining air to blow dry your O-rings or something. Or tell him we got too excited from seeing such and such animal and sucked down that air. I wouldnt worry about the psi issue. I'd worry about my safety stop and getting my buddy and I safely through it.

Sides if Im sitting at 500 she's at 1200 easily, can buddy breath for the safety stop.

What you should take away from scenario : control your breathing! Watch your gauges better, have better communication with your partner, and always do a safety stop unless you'd like some more top time....very long top side interval.

 

[SeaJayInSC]

Yep, once again you guys are spot-on.

We call this, "When the fit hits the shan." It's like there's suddenly a moment of, "Oh, crap" where you realize that you're in over your head a little.

When this happened to me (I was basing this scenario on a real-life situation that happened to me), I was pretty new at all of this, but hung at 20' for the required 3 minutes and then moved to 10'. Hanging out and doing nothing made me sip air, and I ended up surfacing with about 50 psi... But I could have made an emergency swimming ascent from 10' if I hadn't been able to make it last.

The Divemaster began to complain to me a little about the 500 psi thing, but when I pointed out that he'd missed the fact that we'd been right beside the boat for 8 minutes obviously in mandatory deco... And that he'd done nothing to help (like bring us another bottle), he shut his yap.

With my situation, my buddy actually had more psi than I did, so he was fine... He just hung out to donate in case he needed to.

...Know what I had really done wrong? I was watching my computer the whole dive, and when I saw 2 minutes on my NDL, I headed topside. Unfortunately, I took a very long time to surface... Maybe 5 minutes. I thought I was doing some good coming up really slow.

...Which, physiologically speaking, I was - but my computer didn't think so.

Consequently, when I hit 20', I was told to STOP - now with very little psi left.

...So why did I deviate from the plan? Well... For some reason, even though we had a good plan, I decided at depth to instead dive my computer. I thought I could get more bottom time, I guess - it was a new computer and I was a new diver.

It took me weeks to really realize where I'd gone wrong - and that was to stop thinking for myself and start "diving the computer."

I'd have survived, I guess, no matter what, but it was the first time I was faced with a "fit hit the shan" situation... I was painted into a corner, and quite possibly, I didn't have enough gas.

Scared me a good bit.

New scenario:

You're cruising along the bottom at 77'. Vis is fair at best, at maybe 20'. It's somewhat dark, and you and your buddy both have lights, which you're using to point out interesting things along the hull of the wreck. Every once in a while you draw a circle on the hull with your light, for your buddy to see, meaning, "Okay?" He responds by also drawing a circle with his light.

You guys cruise along nicely in formation - side by side, maybe 5' apart, with each of you easily able to look over and see the other.

You look down in a hole to see that there's an open hatchway into the wreck's interior. Looking closer, you see that there's an engine room inside, and you can plainly see engine parts, pipes, and guages along the wall of the interior of the wreck.

Excited, you flash to your buddy to come look at the guages... But there's no buddy.

You look around, but no buddy.

You look into the hole, even cover your light with your hand so that you would pick up his glow. Nothing.

You look around in every direction, then above you... Nothing but a blue-green haze.

Your guages read 1700 psi, and because of the lay of the wreck you know which way to go back to the anchor line. This is an open-ocean dive, and you'd rather not surface off of the anchor line, but will if you have to.

What would you do?

 

[snorvich]

With 1700 PSI, I would have been down for a while, so no decompression time is probably more limiting than air. I would use half of my remaining no decompression time or 300 PSI to look for my buddy, then start slowly up towards the anchor line. (Remember I normally dive solo)

 

[Grunt]

Got a tank banger in this situation?

How big is the diving party on this wreck?

In any case, plan ahead and follow your prescribed rules of buddy seperation. We alway have a plan in case someone is seperated. If you can't find someone within a certain time limit of looking you begin your ascent and perform your proper safety stop. Hopefully your buddies hanging around 15 too. Also never enter a wreck unless trained to do so. Your buddy should know that too.

With proper dive planning there is also usually a spot you meet up on a wreck incase you get seperated. Such as where the mooring line connects to the wreck.

Also we use tank banggers just in case we need to communicate in a low visible situation (no slates, brail diving in missouri, etc), we use one knock for "look at me, or this" and two for "I'm ok" three fast knocks for emergency then a constant knocking until your buddy is within reach.

Plan ahead of time.

I got a situation for you......

So your plan is to replace a mooring line at 95ft. The previous one must be detached, and the new one added on (you have to bring it down with you).

Visibility is nil maybe 3-5ft at best (brail diving as we call it, 3-5 is a great day, usually you cant see anything at all, but use your hands to find your way around).

You descend after your buddy, he is carrying the tools, your carrying the line. You follow the existing line downwards.

After passing into the third thermocline at 75ft you begin to free flow.

What do you do? How do you alert your buddy who may be at the bottom by now?

 

[SeaJayInSC]

<a href=showthread.php?s=&postid=15032533#post15032533 target=_blank>Originally posted</a> by snorvich
With 1700 PSI, I would have been down for a while, so no decompression time is probably more limiting than air. I would use half of my remaining no decompression time or 300 PSI to look for my buddy, then start slowly up towards the anchor line.

Me too - same deal. I'd look around for two or three minutes, making sure not to leave the open hatch - so 15' or 20' in each direction, to look for my buddy. I'd specifically keep the hatch in plain view, since that's where I lost him, and I would assume that he'd come looking for me - back to the hatch - once he realized that I wasn't with him.

Any more than two, maybe three minutes max, I'd head back to the anchor line and prepare for an ascent... All the while keeping my eyes peeled for my buddy - and any bubbles moving skyward (sometimes they're easier to see than the buddy).

Still no buddy on the anchor, I'd start a safe ascent at 30 ft/minute, stopping at 40, 30, 20, and 10 like I've been trained to do even on easy, recreational dives.

I got a situation for you......

Oh, that's a good one, Grunt...

Naturally, the first thing I'd do is switch to my backup, then attempt to repair the freeflowing reg. Usually a good *whack* in the mouthpiece will fix it. Sometimes it helps if you tighten the dials and levers...

If this works, then I'd resume diving on my primary, check my gas (psi) and head to the bottom. Once meeting up with my buddy, I'd get his attention, point at my reg and give it the bird, then signal "so-so" and continue the dive. I'd expect an "okay," and I'd signal "okay" back and finish the job. I'd take extra care to keep my buddy in plain view, by the way, even if it meant touch contact.

If I'd lost more than a couple hundred psi, if I couldn't get the reg to stop freeflowing, or if I wasn't confident about the fix (ie something didn't come out of the reg that was responsible for the freeflow), then I'd abort the dive, signalling to my buddy if I could. If he was out of sight, I'd simply abort and know that he was going to go through the "lost buddy" scenario above.

The situation changes a little bit when this happens at 175' and you're wearing doubles and a stage... But that's another topic for another time.

 

[snorvich]

These are fun SeaJayInSC. Very real world too. If you are not, already, you would make a great instructor. Ok, how about some rescue scenarios.

You are diving the blue hole in Belize (a boring dive by the way) and while at 150 feet you see a lone diver about 15 feet below you. You are at about 1800 PSI and are yourself diving solo. The diver is using his hands and is very slowly sinking. What do you do? Why? If you were buddy diving, what would you do?