Technical Diving - deco planning, trimix planning and general tech dive planning

Hi

i have a few questions about technical dive planning if that ok. i appreciate your time and aswers - thankyou very much.

1) when you do a deco dive as soon as you reach deco does your computer tell you to ascend to your first deco stop? (because if you was deliberatly doing a deco dive then surely you wouldnt want your computer to tell you to ascend until you was ready to)

2) how do you plan your deco dives? - how do you decide @ what depths to make your stops? do you use deco planning software? (if so which version), how do you decide which deco gasses to take (eg 80% o2 ), do you write your deco plan on a slate? when swiching mix underwater do you always watch your buddy switch and do you not swich gas @ the same time? also how do you know how long to stay @ each deco stop? - sorry 4 all these questions

3) when diving with trimix do you use a trimix computer? - if so which one if you dont mind telling me and if not what do you use?

thankyou so much 4 your time and answer - i really appreciate it.

It would be far more irresponsible of me to try explaining the meaning of life

That place called books lets you get on the www with some specific question

1. No, because I don't use a computer, just a bottom timer. If you're using a computer it will usually track your deco obligation as it increases beyond NDL, until you choose to start your ascent

2. I use Decoplanner 3.1.4 software. I generally plan using 50% & 100% as deco gasses & air as backgas, but the software allows you to play around with different mixes and see the difference to the run time/deco. I write the plan in my wetnotes. How closely I check my buddy's gas switch will depend on who I'm diving with - we don't do formal checks as a rule, but I'll look at the bottle markings. We won't necessarily switch at the same time

How long I stay at each deco stop, the first stop depth & the number of stops is determined by Decoplanner, although I may add some time or change the plan according to the conditions...

3. I'm not trimix certified yet, but I would continue to use Decoplanner

YMMV

This should all be covered when you do your Deco Procedures course (yes I know, you're not old enough yet)... if you want to do some pre-study I would recommend getting Mark Powell's Deco For Divers and/or the Deco Procedures manual from the agency you're planning to do your course with (TDI I guess)

craig chamberlain:

Hi

1) when you do a deco dive as soon as you reach deco does your computer tell you to ascend to your first deco stop? (because if you was deliberatly doing a deco dive then surely you wouldnt want your computer to tell you to ascend until you was ready to)

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I only have a Suunto Vytec. It beeps and makes other noises, but it doesn't tell me my first stop. It has a deep stop option, which I don't use. And it also tells me my Ascent Ceiling, but that is not necessarily my first deco stop. Also if I'm diving mix I have it gauge mode anyway, tells me stuff all.

2) how do you plan your deco dives? - how do you decide @ what depths to make your stops? do you use deco planning software? (if so which version), how do you decide which deco gasses to take (eg 80% o2 ), do you write your deco plan on a slate? when swiching mix underwater do you always watch your buddy switch and do you not swich gas @ the same time? also how do you know how long to stay @ each deco stop?

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I use decoplanner 3.1.3 ( I think?) Deco gases depend on the dive. Switches are normally at 1.6pp02, but if I can't get everything to fit within the rule of 1/3rds I will mess with that.
Plan is written on wrist slate for Extended range/ Normoxic dives. Printed off and laminated for Hypoxic dives.

3) when diving with trimix do you use a trimix computer? - if so which one if you dont mind telling me and if not what do you use?

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Nope. Can't afford one.

1) Like Tortuga I use a bottom timer and follow my plan. If I'm not using helium I'll cary my computer (nitek duo) and compare that to my plan. I don't rely on the computer at all and just cary it to compare how much deco it calls for compared to my plan. So far it's cleared way before my plan, but I still stick to my plan.

2) I use V-Planner to plan my dives and then write the plan down in my wetnotes. I tried using a wrist slate on one dive but I felt that it was a little bulky and in the way so I stopped using it and just use my wetnotes which are kept in wet/drysuit pockets.

As for watching switches, I'll pretty much echo Tortugas response. It all depends on who I'm diving with and if they are diving open or closed circuit.

3) I only have very basic trimix training but I use my bottom timer and cut tables for dives using trimix as well.

the wart:

I only have a Suunto Vytec. It beeps and makes other noises, but it doesn't tell me my first stop. It has a deep stop option, which I don't use. And it also tells me my Ascent Ceiling, but that is not necessarily my first deco stop

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If it's like the Suuntos I've used, it will only give you one stop, which will be 3-6m

Tortuga68:

If it's like the Suuntos I've used, it will only give you one stop, which will be 3-6m

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Not quite like that. It has a graduating ascent ceiling. As you do your stops it slowly ticks down in 10cm increments. In theory you can use it to do your stops. I've used it this way once, when the dive was 10 minutes shorter than planned and I didn't want to do the deco for the planned 20 minute dive so I 'flew' the computer. I just followed the stop depths on my slate and watched the ascent ceiling decrease and slowly moved up. I wouldn't want to do it on a regular basis, I prefer my cut tables.

craig chamberlain:

1) when you do a deco dive as soon as you reach deco does your computer tell you to ascend to your first deco stop? (because if you was deliberatly doing a deco dive then surely you wouldnt want your computer to tell you to ascend until you was ready to)

Click to expand...

It sounds like you're thinking about how it would be to conduct a technical dive, using a recreational market capacity computer.

Most computers will give you deco information, but not necessarily present information in a way that's ideal for technical applications.

When you pass into deco, the computer will 'beep' and transition into deco mode. The display will alter and instead of showing a 'No Deco Limit' it will now display a Time To Surface (the total time of ascent, including all stops). It'll also give you a ceiling (your first, perhaps only, stop level) but it won't forewarn you of where those stops will be, or how long they will be at any given level.

You could continue with the dive (watching the 'Time To Surface' increasing rapidly), but you'd need more information than that to be safe. Specifically, you'd need to know your gas consumption. That's impossible to calculate unless you knew where the stops would be... (can you see where this is going?).

As others have said; most recreational dive computers really give you nothing more than emergency deco information. They get you out of a bad situation, nothing more, nothing less.

Specialist technical computers will give you more information than that. They also have better PC-interface, so that you can be sure of pre-planning the dive in advance and understanding the dive plan you will be following.

craig chamberlain:

2) how do you plan your deco dives? - how do you decide @ what depths to make your stops? do you use deco planning software? (if so which version),

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Plan on PC software. Normally V-Planner. You program in the parameters of your desired dive, and it provides you with an ascent schedule. You also program in your SAC and the gas mixes you will use....and it gives your gas requirements.

Have a look here for some different deco software options. There's a few shareware/freeware/trial programmes... that are ok for experimenting with;

Decompression Software

craig chamberlain:

how do you decide which deco gasses to take (eg 80% o2 )

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That's defined by your training and/or personal methodology. Some agencies define what gasses to use. Some divers have personal preferences. Some times you use what you can get....

craig chamberlain:

do you write your deco plan on a slate?

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I do. I print my dive profile from the computer. Laminate it and/or stick it onto a wrist slate. Some divers write, or stick, it into a wetnotes folder.

We normally have our dive plan, plus 2-3 contingency plans (i.e. Just Deeper, Just Longer and Just Deeper + Longer)

craig chamberlain:

when swiching mix underwater do you always watch your buddy switch and do you not swich gas @ the same time?

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Different agencies have different approaches. One thing is for sure; gas switching is one of the most critical aspects of the dive. It's a procedure with lethal consequences for error. Therefore, the skill is taught, replicated, practised, rehearsed and repeated until it is second nature. It should never be taken lightly.

craig chamberlain:

also how do you know how long to stay @ each deco stop?

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As per your dive plan.

craig chamberlain:

when diving with trimix do you use a trimix computer? - if so which one if you dont mind telling me and if not what do you use?

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I don't use a computer for my tech dives. Everything gets set to gauge mode. It then doesn't matter if I am diving air, nitrox or trimix. I follow the plan I've prepared before the dive.

I was thinking of getting a Liquivision x1. That has software options like V-Planner, Gap and MultiDeco. I would still use the V-Planner to plan (and print) the dives. Those profiles would still go onto a slate. The computer would replicate what I'd planned. I could easily switch to a back-up gauge/timer and tables whenever I needed during​ the dive.

You have already gotten an indication that not everyone does it the same way. Here are a couple of highlights.

As Andy said, there is a real difference between a computer truly used for technical diving and a recreational computer. There are computers that masquerade as technical computers because they can do multiple mixes of Nitrox but can't do helium. I would still call them recreational computers. I have not seen anyone on this thread mention a true technical diving computer yet.

As for planning and doing Deco, I have seen all of the following done:

1. Use a system called ratio deco that allows the diver to plan deco in his or her head based on depth and time. Such divers will usually use only some kind of bottom timer.

2. Use software such as V-Planner to plan all the mixes and stops, with the plan written in wet notes, written on a slate, or printed and laminated. Several versions of the plan are created with variations of time and depth.

3. Program gas mixes and a plan into a true tech diving computer computer and follow its guidance. For example, the Liquivision X-1 can run a V-Planner program. Software programs like V-Planner may be used for a backup.

As for what gases to use, people who use ratio deco have standard gases for different depths. Others will use their experience to decide what to use, and they will generally choose something similar to those standard gases. The idea is to limit the amounts of nitrogen and oxygen to specific levels depending upon depth, and most people have about the same idea of what those levels should be.

One of the big differences between recreational and technical diving is in the degree of planning required. When you're doing a recreational dive, in a lot of places, you put on a tank and you go down and dive until your tank gets kind of low, and then you surface or go back to shore. You can't do that with technical diving, because surfacing whenever you want is not possible (this is the ESSENCE of what makes a technical dive). So you start out with the profile you want to dive -- the depths of the wreck or the wall, whatever you know about the site -- and then use a tool, often a decompression program, to calculate the deco you'll need to do for that profile. Then you sit down and calculate the amount of gas you'll need to do that profile and that deco, and add quantities for contingency planning (lost deco gas, lost bottom gas). For complex dives, this planning may start days ahead of the actual immersion.

Training for staged decompression diving includes LOTS of practice in doing all these calculations (because a big mistake in planning may be your last). It also includes a lot of training in how to handle problems underwater (since you can't surface to solve them) and maintaining your poise when you are severely stressed. It's all that underwater experience and polishing that you can't get out of a book.

Staged decompression diving is like all other diving. It's real easy, as long as nothing goes wrong. When something does go wrong (and things DO go wrong sometimes in diving) it can get real hard, though. Not to be taken lightly.