Faith diving and magic?

[DandyDon]

Well Don it makes no difference on the point of the post, and since I believe you are of an age that you will understand the difference between memory and looking at the log on your computer you will forgive my memory differences. the last numbers were from the actual log of the dive, the original numbers from memory.

Hell, I was born with a bad memory, but yeah it gets worse as you survive more years true. That was a major change from your reporting an 80 ft dive and it being a 36 ft dive; if you'd corrected that along the way in this thread, I missed it. I do appreciate your sharing your experiences including your mistakes as it can help us avoid the same - and I need all the help I can get. I really didn't think you could go into deco on a 36 ft dive, even with a prior load - but that may depend on the brand of computer?

I know from my experiences with Coz diving that even an air hog like me can push Ndls with 4/day easily, altho that will vary with sites selected and computer brand - but it's always worth springing for Nitrox on the after lunch deeper dive, even at the excessive prices they charge there for the upgrade. I still find 36 ft max for deco amazing but if so - then I need to allow for it more. I try to check my computers for residual N2 loading as compared to the general dive plan, and DMs will tell you a max for a dive in advance there - even tho you may have to ask.

For my own preferences, I like to make sure I am negative with even an empty tank so I can get down in case I see a boat or jet ski coming in spite of my SMB; yeah being buoyant at a SS is bad. As much as my home bud, insta-buds and I screw up tho, I almost always carry a 19 cf pony on dives which adds to me non-pony weighting, and I have the air!

yes I made a choice to go into deco, it was a bad one and as I have said it was based on thinking the deco was the same as if it were acquired deep. Shallow deco must be worked out at a sufficient delta of depth, so 10ft. not 15 and definitely not 20 and it builds fast. we would have hit deco even if we had immediately gone to the surface, but it would have been manageable and if I had understood the reason for it I would have known to immediately go to 10ft to work it off and not try to do it at 20 and 15ft first. maybe we were at risk and maybe we were not, no way to know, all I can say is the watch said to do it, so we did the best we could.

Ok, all this is in new light now with the depth correction. I guess I just missed it before. I kept thinking you acquired the deco at 80 ft.

It would be neat to see the charts from all 4 dives that day if you can download and share them here?

thanks!​

 

[Atom]

Yall are really funny with this faith in your ability to plan. and your belief that it makes you safe. it is like a catholic and a Jew discussing God.

Real fact, the tables and the computers are all based on empirical evidence that they mostly work. they will not work in every situation and they will not keep every one safe every time. believe in whatever superstition you like until they have a gas monitor attached to your body they are not 100% safe.

You can not dive 130ft for 58 minutes unless you are diving multi levels and the average depth is really something under 60 ft. I dont care what you Expensive toy says or how many deco bottles or nitrox you plan it with, we did it on a single tank of air. and it happens in Coz every day.

fact is we went into deco on a 36ft dive. and did 27 minutes of hang time. how many of you plan for that?

I certainly learned something, you should too.:cool2:

I think you're missing the point. When you plan a deco dive, you plan your depth(s) and time, and work out how much deco you should do. Then take your SAC + depths + times and figure out how much gas you need. Then you add the gas necessary for the various contingencies and factors (lost deco gas, rule of thirds, current, ..). You then make sure you leave with the proper amount of gas, follow your plan, and turn on your time limit or gas supply limit. The plan is much more than just tables + times + deco, a lot of it is about gas and having enough of it. It doesn't guarantee your safety (too many other factors) but it's hell of a lot better than just winging it like you did.

You went into deco without a plan, not only wasn't it planned, it was a failure to execute the dive you were planning (a no deco dive). You believed you'd be alright because of your previous experience, turned out you where surprised by the amount of deco that got added to your dive and you didn't have the gas to do all of it. I'd say lack of adherence to your original plan got you in that spot, that combined with the decision to execute another dive for which you had done no planning so you didn't knew you were not in a position to do it safely. It turned out ok in the end, and I'm happy for you.

We all know tables and computers are built on a model and it doesn't guarantee you won't get bent. Going beyond the NDL also doesn't guarantee being bent. But at some point you have to settle on a limit and stick to it. And the current models are giving good results, so there's a good reason to follow them.

So to end this comment...I don't think we're arguing that you can't drop to 130ft and work your way up (without busting your NDL) without doing extensive planning. We're just arguing that you should know when it's time to leave, either because you're approaching NDL or because you're too low on gas. Since you don't have to do deco, that gas planning is pretty simple (see the rock bottom comments) and not busting the NDL is also dead simple, monitor your computer and act on the info.

Sorry if this comes across as "preaching" or bit condescending, but I really believe that deco is something you plan for not something you just let happen. And for the record, I've done the "1 minute of deco, time to go up, it'll clear anyway" too, I just won't do it anymore.

 

[MauiScubaSteve]

....BTW, you can ride the curve without being on the extreme edge of it.

We were all told that reverse profile dives are inherently bad. That seems to have changed also. Always Do Your Deep Dive First?: Undercurrent 05/2000 .

Things change. Peaceful coexistence does not mean capitulation from either side.

Stay safe.

"...BTW, you can ride the curve without being on the extreme edge of it."

That is well said.

Every dive computer training or briefing I have heard or spoke "emphasized" that it is not recommended to let the NDL time go below 5 minutes. If one follows that, the deeper we are the farther we are from the edge, by percentage.

From what I remember of conversations with Hyper Dick Rutkowski a decade ago, he seemed to be saying that with almost any of the models, squarewaving gives you a statistically similar % of risk. Single box wreck dive, multiple box / wheel or infinite box computer, if you always dive until you have 0 time left at any depth you are now statistically in the zone of most risk for that model.

Sure the science may change, but that does not always mean the practice of deep dives first is likely to change for non military or non scientific divers.

In the first session, a discussion of the literature revealed that the prohibition against reverse profiles probably related less to safety issues than to “optimizing” bottom time over a series of dives. This comes from gas-loading considerations that allow more usable bottom time by making the deep dive first.

 

[lamont]

"...BTW, you can ride the curve without being on the extreme edge of it."

That is well said.

Every dive computer training or briefing I have heard or spoke "emphasized" that it is not recommended to let the NDL time go below 5 minutes.

Yes, you've discovered that if you don't ride the edge of the curve, then you're not riding the edge of the curve.

That's kind of the point, to add some conservatism somewhere if you're pushing the models like that.

And if Dick was literally saying what you remember, I don't think he was doing you a favor. It appears to work okay for multi-level dives to extrapolate from square profiles, but I'll bet if you accurately remembered what he said a decade ago that he mentioned that it would be prudent to add a little conservatism somewhere in the plan if you're pushing it.

If one follows that, the deeper we are the farther we are from the edge, by percentage.

And I'm not sure what you're getting at here, but generally deeper is never more conservative.

Deeper does hammer on faster tissues first which offgas faster so that obligations clear quicker. That's about the only advantage that it offers.

At the same time fast tissues are allowed massive overpressurization gradients by buhlmann and buhlmann-esque models, while models with bubbles and deep stops will not allow as severe of an overpressurization gradient in those compartments -- so I wouldn't come away with the message that you can pound on deep, fast tissues as hard as you like and hop out of the water right when your bend-o-matic clears because I expect that you're running a much higher DCS risk than you think (particularly if you start adding in repetitive dives so that you start the dive with additional free phase load from the previous dive).

 

[lowviz]

Lamont,

If I had to pick three names that taught me the importance of gas planning, yours would be two of them. Trying not to hijack this thread too much, how would the OP plan/guesstimate a multi-level dive with respect to gas required?

Thanks.

 

[lamont]

Lamont,

If I had to pick three names that taught me the importance of gas planning, yours would be two of them. Trying not to hijack this thread too much, how would the OP plan/guesstimate a multi-level dive with respect to gas required?

Thanks.

if you know what the average depth is likely to be, then just ATA * mins * SAC, with appropriate padding for rock bottom. you definitely want to plan the bottom stage of the dive, so 30 min * 4 ata * 0.60 cu ft min = 72 cu ft + 35 cu ft = 107 cu ft -- as you move up you gain more gas from the lower rock bottom and you can 'ride' the rockbottom all the way up.

usually, though, for long multi-level rec dives i'd just use an HP130 tank. with a decent SAC rate you can max out the NDL at 100 feet on 32%, then move up and multi-level for 20 mins from 60->30 and then do 10 minutes from 30->surface, and i'll get out with around 1000 psi still (which is actually enough to deco 2 people for 20 mins). you can futz around with the numbers, but i just know that from experience.

with that kind of deco obligation, though, you really want to start using redundant regs and doubles. i don't think there's any agency teaching that much deco without using doubles.

 

[lamont]

One thing that can be quite useful for planning is your 10 minute SAC rate in psi. That has to be calculated for your tank, but for a 0.55 cu ft / min SAC with a single 130 its about 150 psi / 10 mins / ata.

at 1.5 ata that's 225 psi / 10 mins, or 450 psi for 2 divers for 10 mins.

you can use that pretty easily to work out multi-level profiles.

you can also track your breathing rate that way. i know that i have about a 300 psi / 10 min @ 100 foot in double-130s rate. also about 450/500 psi / 15 mins @ 100 foot in double-130s , which is 1500 psi in Al80 stage at 100 feet for 15 mins. each 1000 psi in double-130s is about an Al80 stage (so total there's 3.5 stages -- or half an Al80 is about 500 psi). i know all those numbers in psi, off the top of my head, without thinking about cubic feet or SAC rates.

 

[fdog]

if you know what the average depth is likely to be, then just ATA * mins * SAC, with appropriate padding for rock bottom. you definitely want to plan the bottom stage of the dive, so 30 min * 4 ata * 0.60 cu ft min = 72 cu ft + 35 cu ft = 107 cu ft -- as you move up you gain more gas from the lower rock bottom and you can 'ride' the rockbottom all the way up.

usually, though, for long multi-level rec dives i'd just use an HP130 tank. with a decent SAC rate you can max out the NDL at 100 feet on 32%, then move up and multi-level for 20 mins from 60->30 and then do 10 minutes from 30->surface, and i'll get out with around 1000 psi still (which is actually enough to deco 2 people for 20 mins). you can futz around with the numbers, but i just know that from experience.

with that kind of deco obligation, though, you really want to start using redundant regs and doubles. i don't think there's any agency teaching that much deco without using doubles.

Kinda like this:

All the best, James

 

[tesnusxenos]

I find more people(who don't have computers) who have too much faith in the dive leader to keep themselves safe. They never plan their dives or even calculate them afterwards they just follow the divemaster (who is often wearing a computer). If they calculated them straight they would be over most days(they could get away with it multi-level diving but they don't know how to and wouldn't take the time if they did know. I don't let my computer get more then 5 minutes away from the nodeco limit. When it approaches I head to shallower water. During my divemaster training I recommended in the briefing that everyone stay above me but people often pay little attention to that.

 

[Bubbletrubble]

During my divemaster training I recommended in the briefing that everyone stay above me but people often pay little attention to that.

@tesnusxenos: Depending on the experience level of the divers in your group, you may want to revise this part of your pre-dive briefing. Although it may work well for novice divers who have no idea how to plan a dive (gas, depth, etc.), I could see more experienced divers being a little put off by such a recommendation.

Best of luck with the rest of your DM training...