Info Why are tables not taught in OW classes anymore?

[EFX]

If somebody is dumb enough to be doing dives deep enough and long enough to go into deco on a single 72 then they need to re-think their diving habits.

Maybe. It depends. If it's the first dive of the day I find that practice questionable at best. However, it's very easy to go into deco on the second dive with a minimum SI. For example, occasionally, I'll do a first dive on air swimming at 50 ft for awile, then swim down to 100 ft, and then back to 50 ft to finish the dive with about 10 to 15 minutes of NDL. I'll spend 20 to 25 minutes on the surface changing tanks, drinking some water, and relaxing before heading back to the water. On the second dive also on air, I'll follow the same profile except I'll lay on the bottom at 100 ft relaxing and watching my NDL creep to 0. I'll begin a slow ascent to 10 ft with 2 or 3 minutes of required deco. At the time of ascent I have 800 to 1000 psi and end the dive with 400 to 600 psi. BTW, all my dives are done with AL80's.

 

[VikingDives]

If somebody is dumb enough to be doing dives deep enough and long enough to go into deco on a single 72 then they need to re-think their diving habits.

While I agree with you, you also have to consider what going into deco is. For example, when I teach, I keep my primary computer set to a GF of 30/70 and my backup computer set to recreational settings identical to what my students use (same computer, conservatism and the same algorithm for my primary and backup computers).

Off the top of my head, with 5 minutes of NDL on the rec side, I will have accumulated 6 minutes of deco on the tech side. The deco obligation will drop to about 2 minutes during the ascent.

But I get your point. Doing deco dives without redundancy is stupid and my dive briefings always include the caveat that we will end the dive at 1000 psi or when anyone is within five minutes of the ndl. . .

 

[Eric Sedletzky]

While I agree with you, you also have to consider what going into deco is. For example, when I teach, I keep my primary computer set to a GF of 30/70 and my backup computer set to recreational settings identical to what my students use (same computer, conservatism and the same algorithm for my primary and backup computers).

Off the top of my head, with 5 minutes of NDL on the rec side, I will have accumulated 6 minutes of deco on the tech side. The deco obligation will drop to about 2 minutes during the ascent.

But I get your point. Doing deco dives without redundancy is stupid and my dive briefings always include the caveat that we will end the dive at 1000 psi or when anyone is within five minutes of the ndl. . .

Alright you guys @EFX & @VikingDives, what happens when you are knocking on the door of a deco obligation on a single 72 and suddenly you have a freeflow, first stage seat melts down or some other unfortunate inconvenience? Let’s say your buddy is also on a single 72 and you’re at your 100’ 0 NDL left, he’s not going to be much help. Are you sure you have enough gas, are you absolutely sure about that? Do you just go for it?
Really really bad idea IMO to get anywhere near NDL’s on a small tank like a 72, or even an 80.
72’s were invented for pretty benign dives to about 60’-70’ way wirhin NDL’s.
Ponies for both if you (big ones) or get a couple 72’s on your back, they’re cheap.
But you know all this I’m sure, you are pro’s. I hope I’m just preaching to the choir.

 

[Joneill]

Maybe. It depends. If it's the first dive of the day I find that practice questionable at best. However, it's very easy to go into deco on the second dive with a minimum SI. For example, occasionally, I'll do a first dive on air swimming at 50 ft for awile, then swim down to 100 ft, and then back to 50 ft to finish the dive with about 10 to 15 minutes of NDL. I'll spend 20 to 25 minutes on the surface changing tanks, drinking some water, and relaxing before heading back to the water. On the second dive also on air, I'll follow the same profile except I'll lay on the bottom at 100 ft relaxing and watching my NDL creep to 0. I'll begin a slow ascent to 10 ft with 2 or 3 minutes of required deco. At the time of ascent I have 800 to 1000 psi and end the dive with 400 to 600 psi. BTW, all my dives are done with AL80's.

That seems a risky dive plan - only a 20 minute SI and then riding to 0 NDL before ascending on the second dive (deco or not)?

 

[John C. Ratliff]

Just so you guys and gals will know, I usually dive High Rocks on the Clackamas River, and the max depth I contend with is 23 feet. It’s really, really hard to get into a decompression problem at 23 feet. I sometimes wear my twin 45s or twin 52s too. But still, decompression is not much of an issue.

I do use, at times, a Cobra dive computer, which is hooked to my HP line on my first stage. It’s a nice, old computer. I would not even think of using redundant computers in these circumstances. There are times I dive the ol’ fashioned way, with my double hose regulators (see my avatar) and simply a J-valve. If the J-valve is inadvertently tripped (hard to do on a reversed J-valve), I simply surface.

What most of you are talking about is resort/boat diving in the tropics, where depth is almost unlimited, and there you need to do things differently. So what you state is common practice in the tropics, with warm water and deep depths possible, is not the environment I normally experience.

SeaRat

 

[boulderjohn]

Just so you guys and gals will know, I usually dive High Rocks on the Clackamas River, and the max depth I contend with is 23 feet. It’s really, really hard to get into a decompression problem at 23 feet. I sometimes wear my twin 45s or twin 52s too. But still, decompression is not much of an issue.

I do use, at times, a Cobra dive computer, which is hooked to my HP line on my first stage. It’s a nice, old computer. I would not even think of using redundant computers in these circumstances. There are times I dive the ol’ fashioned way, with my double hose regulators (see my avatar) and simply a J-valve. If the J-valve is inadvertently tripped (hard to do on a reversed J-valve), I simply surface.

What most of you are talking about is resort/boat diving in the tropics, where depth is almost unlimited, and there you need to do things differently. So what you state is common practice in the tropics, with warm water and deep depths possible, is not the environment I normally experience.

SeaRat

It is possible to get deeper than 23 feet in places that are not in the tropics.

 

[Eric Sedletzky]

It is possible to get deeper than 23 feet in places that are not in the tropics.

Yeah, Norcal.

 

[Joneill]

I got certified (PADI) in 2015 and we did cover the tables in both e-learning and the in-person class part. Computers were covered, but not really deeply - just basic functionality as there are so many different models out there.

In practice, I personally find the tables pretty useless for the type of tropical, multilevel diving I do. However, I did find learning the tables and associated terms/concepts to be very useful in understanding the underlying science of what is going on when diving. That helps me better understand the job that my computer is doing and appreciate the different info it can provide for me.

 

[VikingDives]

Alright you guys @EFX & @VikingDives, what happens when you are knocking on the door of a deco obligation on a single 72 and suddenly you have a freeflow, first stage seat melts down or some other unfortunate inconvenience? Let’s say your buddy is also on a single 72 and you’re at your 100’ 0 NDL left, he’s not going to be much help. Are you sure you have enough gas, are you absolutely sure about that? Do you just go for it?
Really really bad idea IMO to get anywhere near NDL’s on a small tank like a 72, or even an 80.
72’s were invented for pretty benign dives to about 60’-70’ way wirhin NDL’s.
Ponies for both if you (big ones) or get a couple 72’s on your back, they’re cheap.
But you know all this I’m sure, you are pro’s. I hope I’m just preaching to the choir.

I don't think you're following me. In tech mode, I'm in deco, and in rec mode, I'm about 5 minutes from the NDL. So I'm both in deco and within my ndl just because my computer is set in a different mode. I'm like Schrodinger's cat.

I want my students to be conservative, so we start ascents when we are within 5 minutes of the ndl. I wouldn't do what @EFX describes even though I usually dive with an AL40 when doing rec dives. If I can't reach 2 valves that I can feather, I'm not doing any deco.

 

[Bigbella]

In practice, I personally find the tables pretty useless for the type of tropical, multilevel diving I do. However, I did find learning the tables and associated terms/concepts to be very useful in understanding the underlying science of what is going on when diving.

Because we all know that repetitive multi-day, multi-level diving trips didn't exist before the advent of computers . . .