Tec Dive computers and dive plans

[boulderjohn]

At our usual training sync whole,

Be sure to check your voice to text work! (For those who can't figure it out, he actually said "sinkhole.")
.....................

What the OP is doing is getting stuck in a transition from one era of tech diving to another and trying to combine both. Here are those eras as I (at least) experienced them.

ERA 1: Preplan the entire dive, write it down, create a couple contingency plans and write them down, too. Follow your plan to the greatest degree possible, switching to a contingency plan if needed and hope it is reasonably close. No computers used--bottom timers only.

ERA 2: OK, I'll take a computer along, in case something bizarre happens, but I will follow the written dive plan and only use the computer for emergencies. I will set the computer for the closest thing I can come to on my written plans and hope it is reasonably close.

ERA 3: Wait, if I follow the written plan and get too far out of whack with the computer it will shut me out? I will tell everyone I am following my written plan, but I will really follow the computer.

ERA 4: Wow! I can actually input the same settings from my desktop program into the computer, so the two should be the same. Now I will admit that I am following the computer, with the written plan (plus contingencies) as a backup.

ERA 5: I will preplan the dive with desktop software and use the same settings on both my computers. No need to have a written plan if I am reasonably close to the desktop plan.

 

[KenGordon]

ERA 6, how much bailout do I have? That determines my max TTS. Jump in swim round till then.

 

[MaxTorque]

If you are relying only on the computer, which is calculating real time deco, you still need some basic points established surely to ensure your gas planning is valid?

With multi-gas planning this gets even more complex because you may not be able to exhange gas between stops, ie below some depth you may not be able to stop for an increased length of time because your deco gas planned for a shallower stop is hyperoxic etc ?


With regard to leaving one descrete stop depth, it makes sense to ensure that there is enough headroom to hit the next stop at the current tension limits, as during the ascent you will off gas as mentioned. I guess that adds another level of conservatism to the model.

it's really interesting building a model for all this, it makes certain factors really quite clear in terms of importance etc ;-)

At the moment i just have a quick and dirty 1d finite stepping iterative model running in excel, simply because it's really quick to change stuff this way,the plan is to push the maths over to a windows app when i have it sufficiently mature and proven

 

[boulderjohn]

If you are relying only on the computer, which is calculating real time deco, you still need some basic points established surely to ensure your gas planning is valid?

I'm not sure, but you appear to be thinking that people who dive computers just jump in the water and wing it. The dives are still planned ahead of time, so the divers enter the water following the normal tech diving rules about gas calculations. They know their dive plan and generally try to follow it, although the active computer is what is being followed.

Just as an example, about 10 years ago I was part of a group that planned a wreck dive to a maximum depth of 280 feet, and we planned for that and contingencies, using a written plan with no computer. With the size of the wreck and the path we took in exploring it, we were, on average, a lot shallower than our plan, which was not something we could have predicted; our plan was a worst case scenario. We followed the ascent plan to the surface.

In a dive today, we would have made the same basic plan and planned on the same gas amounts, but we would have gotten out of the water a lot sooner but with a lot more gas left over.

 

[MaxTorque]

No, i wasn't really suggesting people fail to follow their plans or leave things to chance, but i was wondering how people achieve that aim in the real world?

I'm slightly surprised there aren't dive computers with a profile target kind of capability. ie download a depth vs time profile into the computer from the matching pc software, and the computer than gives you real time targets and delta's during the dive. That would be really easy to implement and help to close the circle between predive planning and on-dive action.....

 

[boulderjohn]

No, i wasn't really suggesting people fail to follow their plans or leave things to chance, but i was wondering how people achieve that aim in the real world?

It's really not hard at all. It's the same thing as the old written plan except you're looking at a computer instead of a bottom timer and written profile.

I'm slightly surprised there aren't dive computers with a profile target kind of capability. ie download a depth vs time profile into the computer from the matching pc software, and the computer than gives you real time targets and delta's during the dive. That would be really easy to implement and help to close the circle between predive planning and on-dive action.....

I am not sure what you are asking. First of all, you don't need to download a plan into the computer. You can do the plan right on a computer like a Shearwater, although the computer then leaves it up to you to follow it.

Perhaps I am misunderstanding, but I am not seeing the point of what you suggesting. You seem to be thinking that you absolutely, positively, without fail, on pain of death, must follow the plan you cooked up on your desktop software. That plan is an estimate of the depths and times you will encounter. You make sure you have ample gas for that estimate, and then you do an actual dive. If you are on a multi-level wreck, for example, there is no way your estimated plan is going to be very accurate, and there is no reason it has to be. You just need to be sure you don't go beyond the plan so that you continue to have plenty of gas.

 

[boulderjohn]

Here is another thing you may be confused about--how you do team deco stops with a computer v. with a written plan.

When I was using written plans, we would have a designated deco captain. That person would signal when and where we stopped and when we went up to the next stop, according to our plan. We would all obey. During the dive, we had all used slightly different gases (hard to get everything exact) and maybe been at slightly different depths, but we all did exactly the same ascent, because it is important to keep teams together for safety.

When I dive with friends now, one of us will signal that his or her computer says it is time for him to ascend, but it is a suggestion, not a command. The rest of the team will react. Maybe someone needs another minute at that depth, maybe two. They will signal remaining time at that depth. There is no harm in staying a little longer on your deco stop, so the one who could have ascended sooner will wait until everyone is ready, and they go up together. The computers all adjust to the actual time of the ascent, not the time written on a planned profile.

 

[dmaziuk]

I'm slightly surprised there aren't dive computers with a profile target kind of capability. ie download a depth vs time profile into the computer from the matching pc software, and the computer than gives you real time targets and delta's during the dive. That would be really easy to implement and help to close the circle between predive planning and on-dive action.....

It's not actually that easy because users will always $#@! it up. First you need to read in the plan, dealing with all the import errors, then you need to run it and detect all the possible errors in it -- incl. handling potential round-offs that may result in a 1-minute longer, or a 3-metre deeper stop here and there... Same applies to the in-water calculations except there you're guaranteed to have discrepancies between the plan and the real thing.

The fun part is, more code = more bugs.

 

[MaxTorque]

My thought was that the dive computer still runs the normal realtime deco model, and it still is the ultimate arbiter of stops, but that the planning software is used to develop a profile that suits the basic deco profile and the basic gas profile the dive planner wants. That software then say simply spits out a set of basic tables against dive time, which could include depth and Total Tissue Loading for example. Those tables can then be downloaded to the actual dive computer (and CRC'd and parity checked as normal)

During the actual dive, the dive computer can then very easily display a target depth and TTL vs it's dive timer (started as normal by the water contacts being wet and ambient pressure greater than the start depth setting). It could also display an "off target" indicator, tell you how to get closer to your plan. None of that would affect the real time loading calc being done by the computer, but it would allow the diver a very easy way to know where they sit vs their plan, especially when things go bad and you have not actually followed your plan and you now want to know how far "Into the red" so to speak you actually are!

 

[KenGordon]

My thought was that the dive computer still runs the normal realtime deco model, and it still is the ultimate arbiter of stops, but that the planning software is used to develop a profile that suits the basic deco profile and the basic gas profile the dive planner wants. That software then say simply spits out a set of basic tables against dive time, which could include depth and Total Tissue Loading for example. Those tables can then be downloaded to the actual dive computer (and CRC'd and parity checked as normal)

During the actual dive, the dive computer can then very easily display a target depth and TTL vs it's dive timer (started as normal by the water contacts being wet and ambient pressure greater than the start depth setting). It could also display an "off target" indicator, tell you how to get closer to your plan. None of that would affect the real time loading calc being done by the computer, but it would allow the diver a very easy way to know where they sit vs their plan, especially when things go bad and you have not actually followed your plan and you now want to know how far "Into the red" so to speak you actually are!

Dives are not like that though. You might be diving some wreck which is 30m to the sand at one end at 28m at the other. On the day the shot might be at one end or the other. Maybe one end is smashed flat and the other ship shape. You can’t really plan that. It is just 30m for 45 minutes and 15 minutes of deco. There will be some minimum quantity of gas where you must leave the bottom to have enough for the deco and contingencies. So three numbers to remember/write on a slate min gas, 45 minutes and 15 minutes. You can set an alarm for the 45 minutes and one for the gas if you like. But really the dive will not be like that, it will always be shallower. So you could run longer so long as you know you have the gas and don’t exceed your limiting TTS. Get a rebreather and it is all about the max TTS given a worst case bailout.

if you send me your GitHub handle I will give you read rights on my C++ code so save you from excel. It is just command line, no pictures. Have you tried the new fanged lambda stuff on Excel?