UTD Decompression profile study results published

[Jack Hammer]

It will tell you on the fly as you change depth, moving shallower you are going to get more bottom time, no need for any RD voodoo.

A computer will only tell you live as you are doing the dive what your deco is. It wont tell you if it's worth your travel time to swim/scooter over and make that proposed change to the original plan. Flying a computer is very different in the real world from knowing what affect a change you make will have before you make it.

 

[stuartv]

We were on a wreck at like 150' and had lapped it a few times on scooters. We knew another wreck was a few hundred feet away at 130'. We were able to have a quick powwow and communicate a change in plan based on an adjusted avg depth, then scooter over and enjoy the wreck for that remaining time.

How do you classify that as anything other than "did not dive your plan"?

It seems like in the discussion of "plan you dive, dive your plan" there are only 2 ways that people fail: One, they lose situational awareness and they either go deeper or stay longer than what they planned for, by accident. Or, two, they get in the water and make a conscious decision to do something different than what they had planned for.

It seems to me that failing to dive your plan is no more or less forgivable when you do it on purpose than if you do it by accident. What you described seems like it falls squarely in the category of option 2.

Per my training, when I plan a dive, I play for a max depth and a max time. The actual maximums planned for may be ones that are only reflected in contingency plans and not the main plan, nevertheless there is a planned maximum depth and a planned maximum time. No matter what happens during the (presumed technical) dive, I would not intentionally exceed either of those maximums.

In the example you gave, you decide to move over to a shallower wreck site. If you did not increase your planned maximum time, then being a shallower wreck means you really did not need to use RD for anything. Any plan you had for 150' is going to be fine if you only go to 130'. But, if you made a decision on the fly to increase your maximum time beyond what was originally planned for then that is all kinds of wrong, per my training. In other words, it might work for you, but I would not do it.

 

[PfcAJ]

How do you classify that as anything other than "did not dive your plan"?

It seems like in the discussion of "plan you dive, dive your plan" there are only 2 ways that people fail: One, they lose situational awareness and they either go deeper or stay longer than what they planned for, by accident. Or, two, they get in the water and make a conscious decision to do something different than what they had planned for.

It seems to me that failing to dive your plan is no more or less forgivable when you do it on purpose than if you do it by accident. What you described seems like it falls squarely in the category of option 2.

Per my training, when I plan a dive, I play for a max depth and a max time. The actual maximums planned for may be ones that are only reflected in contingency plans and not the main plan, nevertheless there is a planned maximum depth and a planned maximum time. No matter what happens during the (presumed technical) dive, I would not intentionally exceed either of those maximums.

In the example you gave, you decide to move over to a shallower wreck site. If you did not increase your planned maximum time, then being a shallower wreck means you really did not need to use RD for anything. Any plan you had for 150' is going to be fine if you only go to 130'. But, if you made a decision on the fly to increase your maximum time beyond what was originally planned for then that is all kinds of wrong, per my training. In other words, it might work for you, but I would not do it.

If the only tool you have is a hammer, everything looks like a nail.

We changed the plan and we were able to do it easily because we had the tools to do so.

It's only "wrong" if you don't have the ability to do it. We did. Never exceeded min gas, never exceeded max allowable deco, never outran our reserve deco gas. Everyone was on the same page.

If you're on a recreational wall dive planned to 100' but you encounter something cool at 80' do you skip it because you said you wanted to go to 100'? Do you truncate your bottom time because you planned for 100'? Of, of course not. This is no different.

If you're so boxed in that you can't make adjustments do you really have a good hold on the dive and your resources and what they can do?

 

[boulderjohn]

If you're on a recreational wall dive planned to 100' but you encounter something cool at 80' do you skip it because you said you wanted to go to 100'? Do you truncate your bottom time because you planned for 100'? Of, of course not. This is no different.

If you're so boxed in that you can't make adjustments do you really have a good hold on the dive and your resources and what they can do?

I agree. A good dive plan will usually be followed, but there are many times that circumstances change or, quite frequently, your plan could not be all that certain to begin with.

There was a memorable thread about this 7-8 years ago, with some people adamant about the belief that you were an incompetent Bozo if you didn't follow your dive plan precisely every time. One of the most telling responses was from John Chatterton, who suggested that if you can plan your dives that precisely, then you aren't doing very interesting dives. He said that on most of his dives, especially when exploring a new (at least to him) wreck, he had nothing more than a reasonable estimate of what his actual dive would be. He did not know what he would encounter when he reached the wreck. He could not be sure how long he would spend on one deck before moving to another. His dive plans were thus pretty approximate.

He was advocating using two computers, both for himself and his buddy. He felt pretty confident that four computers would not all go bad on one dive. In one other interesting exchange, one of the posters said that doing the math to keep track of his maximum depth on dives gave him something to think about while he was diving. Chatterton responded, again, that if you need something to think about on a dive, you are doing pretty boring dives. On the dives he does, he has plenty to think about, and he was happy to let the computers do that work.

 

[decompression]

Agreed, if you are doing such benign dives that there are zero variables, then dive your plan. You have no requirement for flexibility. However, in many circumstances, there are so many variables that in order to accommodate them, a certain amount of modification is a useful tool. When I did my first tech 1 course, it was cut profiles, the dives we did even at that level, had several "situations" that affected our schedules and that luckily a good knowledge of deco (a shearwater would of been nice) allowed us to mod our stops/times.

 

[stuartv]

If you're on a recreational wall dive planned to 100' but you encounter something cool at 80' do you skip it because you said you wanted to go to 100'? Do you truncate your bottom time because you planned for 100'? Of, of course not. This is no different.

I said exactly nothing about not being able to go shorter or shallower. I talked about not going longer than planned and not going deeper than planned. I also said that if I go shorter and/or shallower, I would have no need to use RD to figure out if that's okay. RD would only be useful if I were going to go longer or deeper than the plan I did before I started the dive. And I would not do that (on purpose).

You said that RD was useful for letting you do a dive that was not the dive you planned. It let you do something shallower. You don't need RD to tell you that you can do that. If you're saying that RD let you do a dive that was longer than the plan you started with, that is where I said it would completely go against the way I was trained (and that if it works for you, that's fine - I just wouldn't do it).

That said, if I started a dive planned to 150, but I knew there was a contingency that might involve spending less time at 150 and then a longer time at 130, I would do a contingency plan for that, too - so that I could do it that way without exceeding my maximum planned time. I call that dive planning and I would do it before I started the dive. And if I were diving from a boat, I would make sure they know the plan and the contingency so that if I exceeded the max time I told them for the 150' dive, they would not think it was an emergency.

 

[RainPilot]

As Mike Tyson said, everyone has a plan till they get hit.

Bear in mind that AJ does cave recovery dives. Any planning for something like that is going to be a guesstimate at best. If you have the ability to adjust on the fly in those circumstances then doing an OW adjustment on the fly doesn't seem like a big deal to me.

 

[rivers]

I said exactly nothing about not being able to go shorter or shallower. I talked about not going longer than planned and not going deeper than planned. I also said that if I go shorter and/or shallower, I would have no need to use RD to figure out if that's okay. RD would only be useful if I were going to go longer or deeper than the plan I did before I started the dive. And I would not do that (on purpose).

You said that RD was useful for letting you do a dive that was not the dive you planned. It let you do something shallower. You don't need RD to tell you that you can do that. If you're saying that RD let you do a dive that was longer than the plan you started with, that is where I said it would completely go against the way I was trained (and that if it works for you, that's fine - I just wouldn't do it).

That said, if I started a dive planned to 150, but I knew there was a contingency that might involve spending less time at 150 and then a longer time at 130, I would do a contingency plan for that, too - so that I could do it that way without exceeding my maximum planned time. I call that dive planning and I would do it before I started the dive. And if I were diving from a boat, I would make sure they know the plan and the contingency so that if I exceeded the max time I told them for the 150' dive, they would not think it was an emergency.

Sometimes things don't go to plan. And not necessarily in a bad way. Maybe you planned for a shallower depth, but it's big spring tides and things are just a little bit deeper. Or you spotted something cool at 45m, and spent most of the dive there instead of your planned average of 42m. Or, as was the case with a dive I did a couple of years back, conditions were that good, you extended your dive as the resources (back and deco gas) were available (including plenty of reserve). As long as you do not extend your dive past the maximum allowed dive time the skipper has set, it's generally not a big deal.
Sometimes, for dives around the 30m Mark, we don't know how long our dive is going to be. A favourite plan is "Jump in, swim around for anywhere from 30-45 minutes, come back up again. Do appropriate deco". We may not know our bottom time as it will depend on conditions at the bottom. If it's a large wreck, we may jump in with a stage of o2, and do over an hour on the bottom.

 

[stuartv]

As Mike Tyson said, everyone has a plan till they get hit.

Bear in mind that AJ does cave recovery dives. Any planning for something like that is going to be a guesstimate at best. If you have the ability to adjust on the fly in those circumstances then doing an OW adjustment on the fly doesn't seem like a big deal to me.

It is absolutely true that I am a relative beginner - and thus why I would not be inclined to take liberties like on-the-fly mid-dive re-planning. And leave me looking at the more experienced divers, like AJ, who say things like what he posted and I can only wonder "is that legit and okay, or is it normalization of deviance that his skill and experience is letting him get away with (so far)?"

All I can conclude is that I don't have the experience to feel comfortable doing what he talked about, nor do I have the experience to judge whether it's perfectly fine or normalization of deviance. I ask questions to try and gain understanding and, hopefully, one day have enough experience of my own to judge for myself.

 

[stuartv]

Sometimes things don't go to plan. And not necessarily in a bad way. Maybe you planned for a shallower depth, but it's big spring tides and things are just a little bit deeper. Or you spotted something cool at 45m, and spent most of the dive there instead of your planned average of 42m. Or, as was the case with a dive I did a couple of years back, conditions were that good, you extended your dive as the resources (back and deco gas) were available (including plenty of reserve). As long as you do not extend your dive past the maximum allowed dive time the skipper has set, it's generally not a big deal.
Sometimes, for dives around the 30m Mark, we don't know how long our dive is going to be. A favourite plan is "Jump in, swim around for anywhere from 30-45 minutes, come back up again. Do appropriate deco". We may not know our bottom time as it will depend on conditions at the bottom. If it's a large wreck, we may jump in with a stage of o2, and do over an hour on the bottom.

I understand all that. But, if your plan is "anywhere from 30 to 45 minutes", wouldn't you actually do a plan for 45 minutes to verify that you have all the gas you need to accommodate that option? I would. In which case, you're exactly where I started - plan for a max depth and max time and then, if you only stay down for 30 minutes, no big deal. You have not exceeded the depth or time you planned for.