first deco dive

[BDSC]

Now I can't figure out who was saying what above. But no matter. We both made our points/ideas known. Time to move on.

(I was talking about ZenDivers last post)

(But since I posted this it has now been cleared up)

 

[ZenDiver.3D]

Now I can't figure out who was saying what above. But no matter. We both made our points/ideas known. Time to move on.

(I was talking about ZenDivers last post)

(But since I posted this it has now been cleared up)

Yep. All good. Sorry about my earlier post. It made total sense at the time.... sorta.

 

[Mr Carcharodon]

but the apparent lack of planning (and his newness to diving) I found a bit alarming.

How much planning would have been adequate for a 2 minute deco obligation? Glancing at your gauge and relizing you have over half a tank left, coupled with knowledge of past dives, was likely enough of a plan. Planning in the water is just as valid as plans done before hand. For "big dives" having more of a plan becomes essential, but I would be hard pressed to call running 2 minutes over NDL a big dive.

Operators in some areas (e.g. Cozumel) routinely run single tank divers well into deco. Essentially none of those divers have a gas or deco plan. I'm not comfortable with that approach but the high sucess rate of those dives makes me question the frothing at the mouth condemnations you see on threads like this.

 

[Codiak]

Back to the OP's question:


Did you have any idea of what your computer would tell you?
If not did you have any idea what you should have expected?

What would have been your reaction if the obligation was 2 hours instead of 2 minutes?
Where you prepare for that eventuallity?

Btw, where was your buddy during this event?
Was he just as prepared as you for the experiment?

Now make your own determination of whether it was reckless or not.

In a later post you state you have a great instructor I'd suggest discussing this with him one on one...

In the end, your alive and kicking so, it was a good dive.

 

[MXGratefulDiver]

How much planning would have been adequate for a 2 minute deco obligation? Glancing at your gauge and relizing you have over half a tank left, coupled with knowledge of past dives, was likely enough of a plan. Planning in the water is just as valid as plans done before hand. For "big dives" having more of a plan becomes essential, but I would be hard pressed to call running 2 minutes over NDL a big dive.

The problem is situational ... let's say you're at 120 feet when you run 2 minutes into deco, and you begin an orderly ascent immediately. Depending on the computer algorithm, by the time you reach 30 feet your computer may have cleared, or it may have continued to pile on deco obligation ... many minutes of deco obligation. Let's say it was the latter (mostly those computers that use straight Buhlmann models or something like them, with some extra "liability padding" thrown in). Suddenly you realize that you're looking at 20 minutes of hang time, rather than the 2 minutes you had when you started up. And depending on your consumption rate and cylinder size, you may suddenly realize you don't have enough gas to satisfy the deco obligation your computer is showing you.

Now, there's a big difference between bending your computer and bending your body ... when I first started doing tech dives I literally bent my computer on every dive, because it didn't give me any credit whatsoever for deep stops ... but I never once bent my body. So how do you make a reasoned decision that it's safe to ascend before your computer tells you to?

These are the sorts of decisions that people are sometimes forced to make when they experiment without truly understanding all the parameters that can affect their dive. Will you be prepared to think your way to the surface safely?

It depends ...

Operators in some areas (e.g. Cozumel) routinely run single tank divers well into deco. Essentially none of those divers have a gas or deco plan. I'm not comfortable with that approach but the high sucess rate of those dives makes me question the frothing at the mouth condemnations you see on threads like this.

This is true in many parts of the world ... Cozumel, Belize, Dahab, and other places that feature "bucket list" deep dives that are routinely visited by barely-trained recreational divers on single tanks. But the fact remains that people do die ... or simply "disappear" ... on these dives from time to time, because they're pushing safety margins a bit thin. Even more frequently, people get bent or suffer barotrauma injuries due to pushing their ascent rate because of insufficient gas reserves. You won't always hear about it ... because that would be bad for business ... but it happens.

The question is ... are you willing to take the risk? Tens of thousands do every year ... and the success rate is quite high. It sucks to be in that tiny minority for whom it doesn't work out so well, though. Is it worth it? That's every individual's call. Personally, I have opted in the past not to do Devil's Throat or the Blue Hole for just that reason ... I didn't think it was worth the risk, given the equipment available to me at the time.

Your mileage may vary ... one person's idea of recklessness may not be the same as someone else's.

... Bob (Grateful Diver)

 

[redacted]

Personally I'd rather that people were basing their diving decisions on sound knowledge of theory rather than blindly following what a bunch of circuits strapped to their wrist is telling them

Knowledge of theory is always preferable to blindly following some reference. Yet we have probably all done the latter and will continue to do it on a daily basis reasonably confident in our experiences. Nothing wrong with circuits or things strapped on our wrist if we have some reason to be confident in their credibility.

How much planning would have been adequate for a 2 minute deco obligation? .

Before or after it appears on the screen? If you wait until after it appears, I think I would consider that reacting, not planning.

As I posted earlier, I chose to test my computer by putting it in deco without putting myself in deco. Just seemed like a safe and simple option.

But if I had chosen to put both of us in deco as the OP did, I probably would have spent a little time planning the deco dive. Depth, time, gas, and a trip to the Navy Air Decompression Tables and determined the stop depths and times as a function of dive times. Then I would have known that in the 80 to 100 ft depth range, going a couple minutes or less beyond NDL would get me a 2 to 3 minute stop at 10 ft. Only real difference from a safety stop is it is not optional. Going a bit longer and I could be looking at up to a 10 minute stop; still not overwhelming. But if I wanted to put my computer (and myself) through multi-level stops, I'd probably have to go quite some time beyond NDL (25 minutes or more) and I'd be looking at total decompression times of at least 30 to 40 minutes which would have quite an impact on gas requirements. Even shorter times beyond NDL (10 to 20 minutes) would put me into fairly long stops at 10 ft; long enough to have to take a hard look at the gas plan. 1500 psi in a single tank is just not much if you start pushing that deco experiment.

 

[Mr Carcharodon]

Honestly I have no idea how you got from a 2 to 3 minute stop to a 40 minute one. You can always paint a scenerio where you will run out of gas. What the OP described was not one of them.

As I said before, I am all in favor of planning, but sometimes you need to plan a lot and others not so much. The OP plan appeared to be to ride his computer to the surface which is problematic for the reasons already noted.

 

[DevonDiver]

As I said before, I am all in favor of planning, but sometimes you need to plan a lot and others not so much.

Neither of which is the same as not planning, or not following a plan.

Even the most 'loosely' planned dive should consist of a basic decision whether it will be a deco, or a no-deco dive. Even the most mentally lacklustre newbie diver could plan to that degree, then blindly follow his instruments to achieve that plan.

Exactly how "loose" are you suggesting that the dive plan could ever be???

Anything less that the above...would mean the plan was essentially comprising of 'get in, get wet, go down, come up...get dry'. :mooner:

 

[LanceLisenby]

The only question here, as far as I'm concerned, is gas supply and maybe thermal issues. If you don't know how your computer will react to deco, you can not know that you have sufficient gas.

A minute or two is probably unlikely to cause an exorbitantly long obligation, so doing so without that knowledge may be benignly reckless, but reckless nonetheless.

Again, this all assumes that the OP did not know how his computer would react. That may be a bad assumption.

The point to the excercise was so I would know how my computer would react. Let me also add that I was already back at the anchor ready to ascend and my buddy was the boat DM since we had an odd number of divers onboard.

 

[redacted]

Honestly I have no idea how you got from a 2 to 3 minute stop to a 40 minute one. You can always paint a scenerio where you will run out of gas. What the OP described was not one of them.

As I said before, I am all in favor of planning, but sometimes you need to plan a lot and others not so much. The OP plan appeared to be to ride his computer to the surface which is problematic for the reasons already noted.

How? Simply by extending my "test" well beyond a 1 or 2 minute violation of NDL.

When I "tested" my computer. I had little idea how much deco it would tell me I needed to do. I did know from the PADI tables, that PADI recommended an 8 minute stop at 15 ft for any violation less than 5 minutes and a stop of no less than 15 minutes for any longer violation. It was not until I obtained a NOAA dive manual that I came to have a bit better understanding about how the deco obligations grew as a function of depth and time.

Once you have that understanding, it is easy to infer that a short violation will incur a very short and manageable deco obligation. I have to hope that the OP had some idea what he was getting into when he decided he had plenty of gas left so he might as well go ahead and "test" his computer in deco.