UTD Decompression profile study results published

[Remy B.]

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.

I don't know nothing and correct me if I'm wrong.

But is not first done a dive to find the victim, place and depth, then a second dive is planned with that data, and then recover the victim? I guess you still can do this with a DC.

 

[Remy B.]

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.

If you do so as you described, staying longer and deeper, then you are eating you gas planned and entering in your contingency gas quantity ( or extra gas in case of Shait hits the fan )

So yes you know you can stay a little longer and a bit deeper because you have that extra gas available that we all put in our planning, so you are getting very tight in that extra gas and you leave less room for when Shait hits the van, it seems to me very loosely taken planning of initial planning modification, the likelihood of shait hitting the van is small but it is there, and it can bight your ars

And as Stuard mention you put in you planning a depth cap that you are actually not diving as a contingency, so you always fulfill your dive plan, but if you go beyond that, you are just playing with murphy's law.

 

[Patoux01]

I find it scary to see how entrenched people are in the "dive your plan" mentality. You can change a plan. If you know what can safely be done with the amount of gas you have, why wouldn't you?

By all means, if you told someone "I'm out at 1015, if at 1030 I'm not here, call for help", then you don't extend a dive beyond that, but changing depth or making it shorter? Fine with me. Or if it's a dive where you're supposed to meet support divers on the way up, but again, that's because you have an "appointment", not because "it's your plan".

If you just agreed "yeah let's do this, should give this bottom time and depth", and you find something interesting 5m further and you know you can safely go I really don't see why you shouldn't, or at which part it becomes "unsafe" or "unforgivable". It's idiotic if you don't know what you can do, that we all agree on...


However, I still don't find this a benefit of RD in itself, it works with any algorithm that you've run a few times and looked for simple rules of thumb in. And it's not in anyway related to the "RD decompression profile". Works perfectly fine with any algorithm that doesn't beg for deep stops and an S-curve etc..

 

[Remy B.]

This dive I did, , I made the planning to 55m, knowing that supposedly it was at 50m to 47m ( depending who you asked ), it ended up recording 52m is the deepest point of the wreck, so I build a depth cap, knowing I have 5m more to play with in the planning.

Guess what, on our way up we encounter current and got worse as we ascended ( abnormal for Curacao conditions very abnormal actually ) so there was a good amount paddling and hiding behind rocks and holding to others and more breathing than normal, so drifting in Deco getting further and further away from the exit spot was not an option, so we had to continue towards the exit point and we had to paddle on our way up, at the point when we were at the sand plato where we were crawling with our hands in the sand and paddling in order to advance and not to overload our self just by paddling, we ended up with eating deep deep into that Deco gas with (zero) bar at surface, completed our deco obligation but stayed longer on the Deco gas because we were working harder , when we shall had got out of the water with 100 bars of Deco in normal conditions, we ended up using our back gas crawling until we got to a saver spot where there was no more current, that was about 20m from the exit point.

now imagine going deeper and longer because you know you can, but the unpredictability of the amount of shait hitting the fan, demands you dive your plan so when shait hit the fan you still have a higher successful rate.

Still don't see the need of using RD, like sometimes happen you get narced more than others I guess you are leaving room to make a mistake calculating your RD, add too that loss of situational awareness due to the N2 effect and it makes a very nasty coctel.

 

[RainPilot]

I don't know nothing and correct me if I'm wrong.

But is not first done a dive to find the victim, place and depth, then a second dive is planned with that data, and then recover the victim? I guess you still can do this with a DC.

Boy if there's someone who knows less than me about recovery dives they haven't been born yet.

But.... the finding part is the one I was referring to where the planning would need to be pretty fluid. Knowing exactly what your resources allow you to do and what effect changing parameters will have would be pretty dang useful I imagine.

We have parallels in aviation. A routine transport flight is a case of plan your flight and fly your plan, with some wiggle room built in for fuel and contingency. Getting creative there would be frowned upon.

Then we have ISR and COIN missions where the starting parameters are backwards. You start with resources and then figure out what you can do with them as the situation develops.

That type of on the fly replanning is not everyone's cup of tea BUT.... once you have all the tools buried in the muscle memory and they have become instinctual it is a very useful way to do business.

 

[PfcAJ]

That is what I'm referring too, if you have a Tec DC, and you know the depth and you know your current dive time at "spot #1" and you know you have 25min more to go to complete your initial planned dive time ( gas quantity ) and it takes 10min to get to "Spot #2" then you know that you have will stay 15min in spot #2 before you start the ascent, why shall you need RD for that ???

I'm very new to diving and I don't understand a lot of things, but I don't see substitute to the DC ot BT or a reason of using RD, meaning that your DC and your buddy's DC or BT need to all fail before you really need to use RD, it seems you need to calculate mentally a lot less by knowing distance and depth of spot #2 having a DC or BT, than adding to that RD.

You're missing the point. We decided to go to the other site which was shallower mid dive. We knew what impact it would have on bottom time and deco obligation before we did it. You're completely glossing over the fact that shallower depth = more bottom time for the same amount of deco time.

A dive computer will not tell you what your deco obligation *will be* during the dive. For that you need something else.

 

[PfcAJ]

I don't know nothing and correct me if I'm wrong.

But is not first done a dive to find the victim, place and depth, then a second dive is planned with that data, and then recover the victim? I guess you still can do this with a DC.

Sometimes.

Last one of these I was involved with we decided to change the plan on the fly because the deceased divers were shallower than we expected. We were able to spend more time shallower and still end up with roughly the same decompression schedule as we had planned for with the deeper dive.

Once you understand the relationship of depth and time to deco in a discrete way you can use this to make adjustments. And I don't mean "if you're deeper you end up with more deco" I mean "if I stay at this depth for 20 more minutes it will tack on 60 more minutes of decompression". Actual numbers.

 

[Jack Hammer]

Maybe I'm wrong but I believe you DC does the same, no need for RD, but what you are doing is even more ill, you are going from shallower to deeper, at least I understand AJ from deeper to shallower because you just get bonus gas.

Remy, you're missing the point. Understanding a simple relationship between depth/time/deco allowed us to evaluate our options and safely adjust our plan underwater. The DC only will only tell us what we can do once we are already doing it, not before.

I don't plan dives using RD and as a whole don't like it because I feel a lot of people use it out of context. Its not something i believe should be taught, but learned through experience. It should not be used as a primary decision maker, it is a mental tool to estimate if something can work.

 

[Remy B.]

fair enough

 

[decompression]

Sometimes.

Last one of these I was involved with we decided to change the plan on the fly because the deceased divers were shallower than we expected. We were able to spend more time shallower and still end up with roughly the same decompression schedule as we had planned for with the deeper dive.

Once you understand the relationship of depth and time to deco in a discrete way you can use this to make adjustments. And I don't mean "if you're deeper you end up with more deco" I mean "if I stay at this depth for 20 more minutes it will tack on 60 more minutes of decompression". Actual numbers.

Like AJ says, it's a simple ratio.......1:2, 1:3 etc. "ratio Deco"