DIR- GUE Why are non-GUE divers so interested in what GUE does?

[kensuf]

Yes, I'm aware of ART, but it is not a pre-req to earning a CCR deco cert through IANTD, where as with TDI AN/Helitrox is a requirement. The point I was making is the last sentence of my post.

 

[ginti]

TDI won't allow a beginning CCR diver to earn a decompression qualification unless they come into the program as an OC decompression diver. I doubt that GUE, which is fairly conservative in their approach to technical training, would turn around and start doing something more aggressive than other agencies.

You have "a bit" (read: enormously) more experience than me, I need to trust you

 

[wetb4igetinthewater]

As slow as possible. Motionless.

open circuit bubbles scare away all the nurse sharks in South West Rocks, Australia. Only the guy on the rebreather got close to them.

 

[Blackcrusader]

Depends. How would you do a 4 hour 70 foot reef dive trying to photograph easily spooked critters?

As slow as possible. Motionless.

open circuit bubbles scare away all the nurse sharks in South West Rocks, Australia. Only the guy on the rebreather got close to them.

You can always switch to an OC setup that reduces bubbles.

 

[Wibble]

Based on the above, one can execute technical dives without a dive computer. All you need is a depth gauge and a timer.

This is the crux of the differences between GUE's approach and just about every other agency.

When I jump into the water, my IQ halves. I am a complete imbecile; I cannot remember which day of the week it is let alone remembering my average depth.

I have a computer to monitor this for me. Actually I have two Shearwater computers, sometimes with a third backup Shearwater computer. They are accurate, extremely reliable, are easy to use and don’t rely on some stupid human (me) to screw up the sums.

Computers are good at that kind of arithmetic, they even keep a tally of the dive (called a dive log). They calculate your decompression obligation and even tell you the time to surface on the fly. They allow you to change things on the fly in an urgency. They adapt the plan to the actual information — there’s enough going on in an ascent without having to think: it just says my next stop is 36m for 2mins.

It’s not the 1990's.

For rough planning, the rules of thumb are OK but not accurate (e.g. 1:1 at 45m, 1:2 at 60m, 1:3 at 75m). You need to run the plan through MultiDeco/whatever for the full planning and bailout constraints.


Why, in GUE’s world, is mental arithmetic considered better and safer than a (descent quality) computer?


(Usual caveat- am not having a go, am genuinely interested in why this technique is still used, let’s all learn together, etc…)

 

[RedSix]

Why, in GUE’s world, is mental arithmetic considered better and safer than a (descent quality) computer?

You didn't get the point.
GUE does not say, that the brain is better or saver than a computer. GUE recommends not to rely on a computer and to be a thinking diver who is in control of the dive. Plan your dive and dive your plan.
Regarding safety and decompression algorithms: the algorithms are only greatly simplified models, which somehow describe decompression. It is not perfectly understood science. Means, if your computer recommends a total decompression of lets say 45 min, it might happen, that on a good day you can cut 15min off and leave the water perfectly fine, while on a bad day even 50min or 55min of decompression are not enough and you end up with pain in your shoulder. So, is the precision of a computer really needed? Or is for "easy" dives a (conservative) rule of thumb close enough?
A very nice side effect of the ratio deco is, that you learn something about decompression and get a feeling (in means of experience) for it.

 

[Adobo]

When I jump into the water, my IQ halves.

Me too.

I am a complete imbecile; I cannot remember which day of the week it is let alone remembering my average depth.

Which is why for dives exceeding 30m/100ft, I am a proponent of using helium. Most of the folks in North America and Europe will be diving in cold, often murky waters. The other agencies that advocate air or lean ean for dives to 45m/150ft, I just don't get it. You folks who went this route are far more robust than I am. I once did a "working" dive at 80ft where we were surveying a pair of sunken amtraks. That dive beat the **** out of me. I was wishing I was diving 30/30 instead of 32.

I have a computer to monitor this for me. Actually I have two Shearwater computers, sometimes with a third backup Shearwater computer. They are accurate, extremely reliable, are easy to use and don’t rely on some stupid human (me) to screw up the sums.

Computers are good at that kind of arithmetic, they even keep a tally of the dive (called a dive log).

Well, there are techniques around this. One of the examples I gave was, a dive with average depth at 150ft for 30 mins using 21/35. I know the deco for this using 50% is 30 minutes - stops every 10ft from 70 on up. This is fairly easy to execute on a boat dive - either pinnacles which is what we have in California or wrecks. The depth average thing plus doing proper stops for deco becomes more complex for beach dives.

Personally, I never used a depth gauge/bottom timer. I always used a computer on gauge mode. This allowed me to capture dive info for logs. Also, you could reset the timer for deco instead of having to remember exactly at what point on your dive your deco began. Recently, I switched to a shearwater perrigrine as it does all the above plus, it is does depth averaging for you. And it is far easier to read than the tec2g I used to use.

They calculate your decompression obligation and even tell you the time to surface on the fly. They allow you to change things on the fly in an urgency. They adapt the plan to the actual information — there’s enough going on in an ascent without having to think: it just says my next stop is 36m for 2mins.

I know what my decompression obligation is for a given dive before I get into the water. I don't need a computer to tell me.

It’s not the 1990's.

For rough planning, the rules of thumb are OK but not accurate (e.g. 1:1 at 45m, 1:2 at 60m, 1:3 at 75m). You need to run the plan through MultiDeco/whatever for the full planning and bailout constraints.

I can't speak to the rebreather aspects but in terms of planning the dive, I will have all my **** sorted out before I leave my house. I know exactly how much bottom gas I will use for a dive (pretty close anyway), how much deco gas I will use. I can tell you with less than 5 mins of error how long my dive will last (assuming nothing goes wrong). We tell the boat that SMB will hit the surface in 35 mins (as an example). When there are multiple teams diving the same site on different profiles, we can even stagger the start of the dives (one team goes in 10 mins ahead). First team says their bag will hit the surface in 45 mins from descent. Second team's bag hits the surface 35 mins from their descent. The boat crew sees both bags hit the surface almost exactly the same time.

Why, in GUE’s world, is mental arithmetic considered better and safer than a (descent quality) computer?


(Usual caveat- am not having a go, am genuinely interested in why this technique is still used, let’s all learn together, etc…)

I remember chatting with someone who was trained in the same way as you are describing - "run everything through your dive computer" type. I asked him, on a 150ft dive for 20 mins, how much deco do you do? How much deco gas will you need? How much bottom gas will you use? His answer was, I dunno. I need my dive computer. Any tech 1 diver will be able to do the math on how much gas is needed on a piece of paper in less than 5 mins. And the deco is 20mins (2s and 5s) using 50%. He said, what if the dive runs 5 mins long? I said, deco is 25 mins.

For me, I feel the other way around. I can't fathom getting in the water not knowing how much deco I will need to do for the dive I'm about to do. Not having some sense of how much backgas or deco gas I will need. And this whole "time to surface" thing - Could someone explain to me what that means? I mean, I always know once my deco starts how much time it will be before I surface. Its a product of knowing how much deco I will need to do before I get into the water. I have no idea how you do contingency planning with your gas without knowing how much time it will take you to get to the surface - in advance.

 

[Wibble]

You didn't get the point.

You're right there.

GUE does not say, that the brain is better or saver than a computer. GUE recommends not to rely on a computer and to be a thinking diver who is in control of the dive. Plan your dive and dive your plan.
Regarding safety and decompression algorithms: the algorithms are only greatly simplified models, which somehow describe decompression. It is not perfectly understood science. Means, if your computer recommends a total decompression of lets say 45 min, it might happen, that on a good day you can cut 15min off and leave the water perfectly fine, while on a bad day even 50min or 55min of decompression are not enough and you end up with pain in your shoulder. So, is the precision of a computer really needed? Or is for "easy" dives a (conservative) rule of thumb close enough?
A very nice side effect of the ratio deco is, that you learn something about decompression and get a feeling (in means of experience) for it.

I know my decompression gradient factors -- 50:80. I know it works as I've done hundreds of decompression dives using those values. I also know that I can pad the last stop if I think I'm in need of more hydrobaric therapy, maybe using a surface GF of 70 or even moving up to 3m/10ft for the last stop (I find I get less tired if I do that).

PFO aside, Buhlmann works for millions of dives and the old rows over bubble models and deep stops has been pushed aside with most people coalescing around Buhlman 50:80 or recently 50:70.

Ratio deco is a very approximate highly simplified system so that divers can do it in their head without paper. Buhlmann+GF is a 16 compartment model that requires a computer to make the calculations.

Again, why push ratio deco when there's perfectly good computers that will keep a track on your dive profile and adjust the decompression schedule?

I remember chatting with someone who was trained in the same way as you are describing - "run everything through your dive computer" type. I asked him, on a 150ft dive for 20 mins, how much deco do you do? How much deco gas will you need? How much bottom gas will you use? His answer was, I dunno. I need my dive computer. Any tech 1 diver will be able to do the math on how much gas is needed on a piece of paper in less than 5 mins. And the deco is 20mins (2s and 5s) using 50%. He said, what if the dive runs 5 mins long? I said, deco is 25 mins.

The reason for that is you're using the 1:1 approximation which requires standard gasses, e.g. 21/35. Of course for a dive to 45m/150ft you could use 25% oxygen (which will reduce your decompression time) and less helium, say 25% which gives you 25/25 which is much cheaper than 21/35 -- that's assuming you can get helium for open circuit diving nowadays.

I know I keep going on about helium availability and pricing. The days of diving 21/35 or 18/45 on open circuit are pretty much over. Rebreathers are the only future for deep diving -- I need about 120 litres of diluent for a deepish dive, so about 60 litres of helium for a 70m/230ft dive, compared with 2,500 litres of helium for open circuit. At 5pence/cents per litre (it is considerably more than that in some places) that comes to £3/$3 on a rebreather or £125/$125 on OC.

 

[Adobo]

The reason for that is you're using the 1:1 approximation which requires standard gasses, e.g. 21/35. Of course for a dive to 45m/150ft you could use 25% oxygen (which will reduce your decompression time) and less helium, say 25% which gives you 25/25 which is much cheaper than 21/35 -- that's assuming you can get helium for open circuit diving nowadays.

I'm gonna keep it short as I need to get to bed but..

I don't use a standard gas so I can do a 1-1 approximation for deco. Well, that is not the only reason. The other reason is that I dive within a team. Sometimes a team of 2. Sometimes a team of 3. Sometimes you start as a twosome but another diver had a buddy flake and now wants to join your team. Standard gases and standard approaches to deco (that accommodate adjustments that the team agrees to) help facilitate all that.

I know I keep going on about helium availability and pricing. The days of diving 21/35 or 18/45 on open circuit are pretty much over. Rebreathers are the only future for deep diving -- I need about 120 litres of diluent for a deepish dive, so about 60 litres of helium for a 70m/230ft dive, compared with 2,500 litres of helium for open circuit. At 5pence/cents per litre (it is considerably more than that in some places) that comes to £3/$3 on a rebreather or £125/$125 on OC.

Let's call it $150 to refill my backgas, deco and argon bottles. Sounds good. I'll do that all day if I can avoid the complications of a rebreather.

 

[RedSix]

Again, why push ratio deco when there's perfectly good computers that will keep a track on your dive profile and adjust the decompression schedule?

Because both, computer and/or your brain can / will fail. Using a good computer and your brain reduces the probability of a major error. Without using your brain you might not even notice that the computer fails. And computer make failures! Maybe not the Shearwater, but I already heard bunch of stories about others.
To be in control of the dive, you need to know what to expect of the dive in regards of decompression obligation and gas usage. So you somehow need to know this before you start the dive and not during the dive. Ratio deco is only an very simplified model for a very small amount of dives. But nonetheless it gives you an idea of what to expect. Build your experience and be in the driving seat, nothing else. A few rules of thumbs which makes planing a few dives easier. Without the need to use a special decompression software.