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

[Dive Bug Bit Me]

You already have a number of very good answers to your question. Your post, did, however get me thinking about what I would do if I was 16, keen on technical diving and waiting for the calendar to tick away so that I could do the courses I really wanted. As a thread hijack, I would probably do some combination of the following;

1. Dive. There is a lot of agreement that there is no substitute for time in the water.
2. Focus on buoyancy and trim. Recreational buoyancy is easy. However before you contemplate tech, you should be able to go into a hover over a piece of corral. Don't move more than 6 inches in any direction. Do this in perfect trim. Take your mask off and continue to hover for a few minutes without moving more than 6 inches. Maybe turn upside down and hover watching the surface of the water (again 6 inches max movement).
3. Learn the frog kick and try never to use anything else, never skull with your hands (even if you need to carry a camera just to keep yourself from using your hands to swim).
4. Learn to control your entire dive with just one hand do a left hand only dive. Do a right hand only dive.
5. Learn how to move your head, hands and legs to get into any trim position underwater. Without finning, I can roll into a head stand and then rotate back to be fins down (buddies will love it when you do head stands on the safety stops without changing depth or finning).
6. Get yourself a set of doubles (or side mount rig) and learn to dive these. All buoyancy and trim basics above should be easy in a set of doubles. Do get an appropriate instructor to show you the valve shut downs.
7. Learn the back kick and modified flutter and practice these on dives.

I was able to do all of the above before my first tech course and benefited tremendously. If you are on a course, you don't want to be thinking about buoyancy and trim, but rather about the new skills you are learning.

In terms of some useful training, you may consider a combination of recreational wreck diver, cavern diver (parental consent required), peak performance buoyancy.

 

[down4fun]

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)

As has been said most recreational computers are not set up for real decompression diving. If i remember right my recreational computer would send you right to 10 feet for all deco. A technical computer, at least X1 and Shearwater, will track your depth and time and calculate your decompression as it accumulates, this is shown as TTS or total time to surface. It will also show the depth for your first deco stop. Once you arrive there it will show you how long you are to stay there, then once that stop is completed it will indicate to move up to the next depth, and so on.

) 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

Like most everyone here I start with a software program usually Vplanner. Myself and the rest of the team will then plug in the depth of where we are going and work backwards from there. We, my buddies and I, are all on rebreathers so the the limiting factor is usually bailout gas. Vplanner has a feature that will calculate bailout based on the sac rate you put in for the deepest and longest point of the dive. If we do that calculation and can carry the amount of gas necessary, plus reserve then the dive plan is good. But sometimes the gas required is more than we have or want to carry so we may shorten the bottom time, or decrease the amount of time in the deepest part to lessen the gas needed. Once all this been planned and the team is agreement I will put the ccr plan (no bailout emergency) and the bailout plan on tape on my computer. I will dive the computer, and have the tape tables as a back up. As far as deco gases we carry pretty standard mixes. 50% and 100% and a bottom bailout gas.
Also when i was o/c and doing technical dives we would not switch gases at the same time. It was you watch me then I watch you. But then we are pretty geeky i guess. We would go spend entire dives in the sand at 60 feet or whatever, doing drills to practice for the bigger 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?

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

When I first started out o/c I did not have a trimix computer. I ran tables and strictly tables. And I think there are some positives to learning that way. Now that I am on a ccr I have two shearwaters that both have trimix decompression software in them as does my primary buddy. I think almost all the ccr divers i dive with here are running two shearwaters. One plugged into the ccr and the other maybe wired in or run stand alone.

 

[Dsix36]

.................................... But then we are pretty geeky i guess. We would go spend entire dives in the sand at 60 feet or whatever, doing drills to practice for the bigger dives. ..........................................

What do you mean "GEEKY", I still do this.

 

[down4fun]

What do you mean "GEEKY", I still do this.

As do I. I'd like to think it's part of the reason we are still around

 

[Centrals]

1. Deco dive is pre-planned NOT by accident. I use TWO bottom timers for deco dive. Plan the dive, dive the plan.
2. Pro-Planner and Deco Planner. 50% and 100% O2 for deco. Gradient factor set at 20/80. The soft ware will work out the profile which I write it on a slate. All team member dive the same profile. For those who have tech computers will still follow the original dive plan. Computer is for back up.
3. There is no difference between air, nitrox or trimix dive. But for the trimix dive, the deco gas is more critical.

 

[boulderjohn]

As has been said most recreational computers are not set up for real decompression diving. If i remember right my recreational computer would send you right to 10 feet for all deco.

That was said earlier in the thread regarding Suunto's, and it really isn't accurate. These computers will send you right to 10 feet, or rather normal safety stop depth, for minor deco obligations. For the most part, so will tech computers. If you incur serious deco, they will stop you much deeper, depending upon their algorithms.

A number of years ago, before I had any tech training, I went to 180 feet on the San Francisco Maru on air with a Suunto Cobra (I know, I know.), which is about as recreational as computers get. I don't remember at what depth it put my first stop, but it required a series of short stops until I did a massive stop at 15 feet.

 

[Rhone Man]

As has been said most recreational computers are not set up for real decompression diving. If i remember right my recreational computer would send you right to 10 feet for all deco.

I don't believe that is strictly correct. Certainly mine (a Suunto and a Sherwood) move to deeper ascent ceilings with time. But they certainly seem focused on getting you as shallow as possible as quickly as possible (which is probably appropriate for "accidental deco" whereas a rather more conservative profile would be appropriate to a "planned deco schedule).

To the OP: If you do plan on doing deco dives using "recreational" computers, you must remember to stick to you deco schedule and resist the (strong) temptation just to push yourself all the way up to the ascent ceiling on your computer for the reasons set out by Wart and Andy (DevonDiver).

 

[vinegarbiscuit]

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.

I am just starting out along this road, so take it for what it's worth:

1). So far, I'm using only a bottom timer (my recreational computer set in gauge mode) and tables generated via V-Planner. However, I entered soft deco when working toward my Apprentice level cave qualification, and was using a decompression computer. The display showed (as Devon Diver stated) a "total time to surface", which was easy and simple enough to read. However, I knew what to expect (and had only one hang, at 15-feet, so it wasn't hugely complicated. I expect to take delivery of a new decompression computer soon, but I'll still cut tables and follow what's most conservative.

2). For class, I planned my decompression dives using good ol' IANTD tables. My instructor provided some input - "be sure that you plan for this depth, and that there are no stops below 20-feet", which gave us guidance about the desired run-time - but that was about it. The depth and duration of all decompression stops were clearly listed on the tables. We had to show ALL the sums behind our calculations - CNS/OTUs, anticipated gas consumption, total run time, the whole lot. Also for contingency plans (5 feet deeper, 5 minutes longer, and both), and ensure we had plenty of back gas and deco gas for all eventualities. Upon graduation, I was told to use V-Planner (which I was already quite familiar with, having watched my SO tinkering with it for the last couple of years). But it's very good to know the maths, so you can best appreciate what your deco software is spitting out.

Here in Hawaii, gas selection is driven by availability. It's easiest to go with EAN 36 and 100% O2. Hardly anyone likes partial-pressure blending 50% or 80% here, whereas practically every dive shop banks EAN 36. OK, there may be a little more hang-time as a result, but the water is warm and clear, so it's not exactly onerous. Back home in the Northeast US, where it's easy to get 50%, I'll probably start carrying that instead of nitrox. Plus, that's what other folks are carrying, which is a consideration. And finally, with that cold-ass water, I want to be back on the boat sharpish; that's another consideration when selecting deco gas.

I write my plans on a multi-page wrist slate. I like having my plans close to hand. Eventually, I'll learn how to print everything so it fits on my slate - all my attempts so far are too big or too small - so I don't have to read my wonky hand-writing.

If my buddy and I are diving the exact same plan - depths, run time, deco gasses and the whole shebang - we monitor each other's gas switches, and switch at the same times and depths. If not, then I do my own thing, and he does his. For example: my current instructor dives a rebreather while he's schooling me. There's no need for him to 'switch gasses', since he basically has a mixing station on his back, so he just hangs out and doesn't blow bubbles in thast very freaky way that rebreather divers so, while I make my switches on open-circuit.

3). I am not trimix certified, but inherited a Dive Rite Nitek He from my SO and hoped to use during my training (whenever that will be). However, it's since died, and the Nitek X that the manufacturer replaced it with has also died. They've promised to send us a Nitek Q that's already unlocked for trimix and CCR use (for my SO), so we'll see what happens.

 

[down4fun]

That was said earlier in the thread regarding Suunto's, and it really isn't accurate. These computers will send you right to 10 feet, or rather normal safety stop depth, for minor deco obligations. For the most part, so will tech computers. If you incur serious deco, they will stop you much deeper, depending upon their algorithms.

I don't believe that is strictly correct. Certainly mine (a Suunto and a Sherwood) move to deeper ascent ceilings with time. But they certainly seem focused on getting you as shallow as possible as quickly as possible (which is probably appropriate for "accidental deco" whereas a rather more conservative profile would be appropriate to a "planned deco schedule).

you could both be correct. The times i saw the deco obligations on my recreational computer is was a very small obligation. Once I started to do deco dives "for real" I put the hockey puck in gauge mode and dove tables.

 

[ianr33]

My Aeris computer starts with a deco stop at 10 feet and after a while goes to 20 feet,30 feet etc.

You have to try pretty hard to get it indicating a 20 foot stop.(for a normal 100-120 foot dive probably asks for 20 minutes at 10 feet before it requires the 20 foot stop) Anyone doing that unplanned on an 80 has seriously messed up and probably will not have enough gas to follow the computers stops.