Technical Diving without Dive Computers

[Random Dude]

Hi all, I have a few questions pertaining to dive planning in the technical realm that I hope other members on this board can enlighten me on.

1.How do divers doing technical dives with bottom timers or gauge mode only actually go about their decompression planning? My impression is that they use decompression software to calculate out a plan, record the plan on slates or wetnotes, then follow the plan on their dive. However, how do they factor in changes that occur on the dive? (i.e. Different surface intervals, shorter dive time, longer dive time, extra exertion due to emergencies etc)
I am primarily interested in how one can implement Buhlmann ZHL-16C with GFs without a dive computer, as I am more convinced by the research, logic and flexibility behind this algorithm as compared to other algorithms such as VPM or RGBM.

2.How relevant is Ratio Deco still in modern technical diving, given that RD actually (to the best of my knowledge) emphasises deep stops more than what contemporary literature suggests is wise? Gathering from books, articles and videos from Mark Powell, David Doolette, Simon Mitchell, Neal Pollock, and other divers and researchers, I had the impression that RD would not be really useful in technical diving.

3.Lastly, for recreational diving to deeper depths (30m~40m), is there any value in planning the dives with the same methods and mindset used in technical diving?

Hope the other divers on this forum can help me find answers to the above questions, and any constructive discussion would be much appreciated. Thanks in advance!

 

[doctormike]

1) Dive planning is done ahead of time, generally using dive planning software. You could also use tables, but I believe that for complex plans, software is better, especially since there wouldn't be a table available for every possible combination of deco gasses. Square or multi-level profiles are decided on in advance, the necessary ascent schedule and gas switches are determined, and this plan is written on a slate or other surface. A limited number of contingency plans are also calculated ahead of time, for example overstaying by 5 minutes, going deeper than the planed maximum depth, as well as "lost gas" scenarios (where you don't have access to richer deco gas and have to decompress fully on your back gas).

Other than the contingency deviations from the plan that you calculate ahead of time, you wouldn't be able to modify your ascent schedule on the fly for arbitrary random changes - that would be one use of a dive computer. For example, if you end up being much shallower than you planned, you would get "credit" for that and not have to do as much deco if you had a computer with you on the dive.

2) Don't know anything about this

3) Sure! Tech diving isn't only about going deep, diving longer, or going past NDLs. It's a mindset of pre-dive planning that can be helpful to any diver.

 

[PfcAJ]

Hi all, I have a few questions pertaining to dive planning in the technical realm that I hope other members on this board can enlighten me on.

1.How do divers doing technical dives with bottom timers or gauge mode only actually go about their decompression planning? My impression is that they use decompression software to calculate out a plan, record the plan on slates or wetnotes, then follow the plan on their dive. However, how do they factor in changes that occur on the dive? (i.e. Different surface intervals, shorter dive time, longer dive time, extra exertion due to emergencies etc)
I am primarily interested in how one can implement Buhlmann ZHL-16C with GFs without a dive computer, as I am more convinced by the research, logic and flexibility behind this algorithm as compared to other algorithms such as VPM or RGBM.

2.How relevant is Ratio Deco still in modern technical diving, given that RD actually (to the best of my knowledge) emphasises deep stops more than what contemporary literature suggests is wise? Gathering from books, articles and videos from Mark Powell, David Doolette, Simon Mitchell, Neal Pollock, and other divers and researchers, I had the impression that RD would not be really useful in technical diving.

3.Lastly, for recreational diving to deeper depths (30m~40m), is there any value in planning the dives with the same methods and mindset used in technical diving?

Hope the other divers on this forum can help me find answers to the above questions, and any constructive discussion would be much appreciated. Thanks in advance!

1. Plan your dive, dive your plan. You’ll have contingency plans for +- bottom time, and have stuff worked out for loss of deco gas. In my experience the tables and a computer are always within a few minutes of one another. The benefit to tables is that it helps you easily visualize trends between bottom time and deco time and they’re “fixed”. If you don’t press a button on your computer (like at a gas switch), the tables are still “right”.

2. Ratio deco is simply identifying a trend between depth time and decompression requirement and using that trend to adjust your decompression based on what you did on the dive. Maybe for every 5mins at depth, you end up with 10mins of decompression according to whatever algorithm you choose. If you do 15mins on the bottom, you get 30mins deco. Neat. But say you go over time for whatever reason to 20mins. Now you know you have 40mins deco. It’s quite handy. Your algorithm may or may not incorporate deep stops, and you can use ratio deco to reflect that as appropriate.

3. I think there’s a ton of value in that. Helps assure you have enough gas to complete your dive, and it helps you be aware of your decompression requirements.

 

[Slamfire]

1. I don't have much more to add to this point. @doctormike did a pretty good job answering this. I'll only expand on saying that if you end up doing shallower or shorter bottom times, oftentimes we would still follow our original deco plan without deviating since it would add conservatism. In other words deviations that pad your conservatism are perfectly acceptable. Deviations that increase your risk, not so much. Yes, you do plan for contingencies, but you do your best not to go into contingency territory. It is always a good idea to aim to surface with your contingency supplies intact and without having had to use your redundancies.

2. RD is only one flavor of a computerless deco on the fly. @Doppler in his Six Skills book describes a deco on the fly methodology that complies within vpm profiles and these often have shallower stops than utds RD. To me, the value of a deco on the fly methodology is that it gives you one more tool and one additional level of redundancy. Competency using it also helps divers understand deco dive planning and execution nuances more deeply.

With all that said, I still wouldn't use deco on the fly as my primary dive planning and execution tool. I believe GUE recommends it as a backup, just like @Doppler does in his book.

UTD recently came with RD 2.0 with slightly shallower deep stops which are still too deep for my personal taste.

My tools of choice are to cut a plan on a desktop or mobile planner. Share it and discuss it with my teammates and then execute it while we carry our Shearwaters on the same settings that we used on our desktop planners. A perfectly executed plan then matches exactly with what the Shearwater is telling you to do. There are no surprises and if you want to take advantage of any of the credits that @doctormike mentions, your dive computer will let you know just how much credit you got.

3. Most definitely. The degree of attention to detail in technical diving can certainly be applied to recreational with favorable results. Think about NDLs and safety stops and then look at it from the perspective that all dives are deco dives. Dives within the ndls still produce gas loaded tissues and bubble formation. Hence all dives are deco dives. @Doppler in his book talks about an ascent behaviour that is equally applicable to technical dives with mandatory stops just as it is with dives within the ndl.

 

[doctormike]

1. I don't have much more to add to this point. @doctormike did a pretty good job answering this. I'll only expand on saying that if you end up doing shallower or shorter bottom times, oftentimes we would still follow our original deco plan without deviating since it would add conservatism. In other words deviations that pad your conservatism are perfectly acceptable. Deviations that increase your risk, not so much.

Totally agree. I didn't mean to imply that planning goes out the window if you just fly your computer. The only time I would do less deco than the original plan would be if there was a huge difference between the plan and the actual dive. Sure, doing extra deco is never a problem, but sometimes you plan for a big dive and then for some reason you do a MUCH shorter or shallower dive - I think that in that case it's OK to follow your computer, padding that with extra deco as well.

Yes, you do plan for contingencies, but you do your best not to go into contingency territory. It is always a good idea to aim to surface with your contingency supplies intact and without having had to use your redundancies.

Right, the contingencies are for emergencies. They aren't really meant to be options for hanging around longer because you are having fun. If you decide "hey, I'll just run my +10 minute plan instead because it's a great dive" and THEN you have a problem, you have lost your backup.

 

[tomfcrist]

It’s rare that the answer to a question is adequately expressed even on a 20 page thread here...so count yourself lucky to have gotten very adequate answers in the first two responses.

In my opinion, a good tech capable computer should be a tech divers absolute LAST investment. Running written schedules is more than just adequate..it’s simpler and foolproof if done correctly.

Save the money and use it toward adequate equipment, training and most importantly, diving. I can hit 10 offshore charters for the cost of a shearwater.

 

[Red Sea Shadow]

How do divers doing technical dives with bottom timers or gauge mode only actually go about their decompression planning? My impression is that they use decompression software to calculate out a plan, record the plan on slates or wetnotes, then follow the plan on their dive. However, how do they factor in changes that occur on the dive? (i.e. Different surface intervals, shorter dive time, longer dive time, extra exertion due to emergencies etc)
I am primarily interested in how one can implement Buhlmann ZHL-16C with GFs without a dive computer, as I am more convinced by the research, logic and flexibility behind this algorithm as compared to other algorithms such as VPM or RGBM.

Download the Lite version of Ultimate Planner and give it a play. It's free, and it incorporates various flavors of ZH-L16 along with VPM-B and M11F6 (another dissolved gas model, not as famous as ZH-L16). Read the inline help to see how to cater for longer/deeper plans.

 

[Random Dude]

Thanks a lot for the replies!

I am currently using Subsurface which I've found quite intuitive to use. However, I've yet to incorporate technical concepts such as rock bottom and decompression plans into my recreational diving. Gonna go for the TDI AN/DP courses first to ensure that I'm not missing out on any important parts.

It's free, and it incorporates various flavors of ZH-L16 along with VPM-B and M11F6 (another dissolved gas model, not as famous as ZH-L16)

What's the M11F6 algorithm? I've seen it being mentioned a few times, but have not been able to get any solid information on this algorithm. Also, are there any other more "modern" algorithms that's based on more recent studies and science that I should be aware about?

 

[KevinNM]

What's the M11F6 algorithm? I've seen it being mentioned a few times, but have not been able to get any solid information on this algorithm. Also, are there any other more "modern" algorithms that's based on more recent studies and science that I should be aware about?

Offhand I don’t know. Deep into Deco has what seems like a pretty good survey of decompression models.. There are more than you might think, though how many are widely used is another question.

 

[Centrals]

I was taught to use Table(IANTD) back in 1998 and I am still tec diving without a dedicated dive computer.