Info Why are tables not taught in OW classes anymore?

[dmaziuk]

That’s still really vague.
How about something like
“You are allowed to go through a swim through if: A) you can see an exit visible from the entrance before entering the swim through that appears to be large enough to allow an passage.
B) The swim through is 25’ or less in length.
C) If the visibility is too low to see out the other side and the swim through length is unknown and potential hazards unknown, then do not enter.”

I bet that'll be real popular on Roatan.

 

[tursiops]

I am reasonably sure that this is incorrect. SB members who know agency standards should comment. You need to be able to CESA from 130 ft for it to be a recreational dive, I don't think so.

There is no requirement in PADI for a CESA from 130 ft in any situation, much less the definition of a recreational dive.

 

[Eric Sedletzky]

I bet that'll be real popular on Roatan.

I’ve never been there.

 

[boulderjohn]

That’s still really vague.
How about something like
“You are allowed to go through a swim through if: A) you can see an exit visible from the entrance before entering the swim through that appears to be large enough to allow an passage.
B) The swim through is 25’ or less in length.
C) If the visibility is too low to see out the other side and the swim through length is unknown and potential hazards unknown, then do not enter.”

This would be something comprehensive with at least some written rules.

You seem to be unclear on the concept of "diver judgment."

Yes, there is (or will be) guidance on the things that people should consider when deciding if a swim-through is right for them. I wrote an entire course on this. It was entitled Understanding Overhead Environments. It is an approved PADI course. I can't teach it to you, though, because I have retired from teaching.

 

[EFX]

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?

When I do those dives of light deco that I describe above I'm doing them solo and I always have an alternate gas source.

 

[EFX]

Could you provide me with an example (real or hypothetical) of a multilevel dive that would be "allowed" by depth averaging the tables but that would overstep the limits of (i.e. lead to deco in) Buhlmann with a GF hi of 85, for example? I don't even know how to do this, outside of comparing it to actual dive profiles (and I don't have any with deco incurred since I'm not trained for that).

I don't know about depth averaging but I did compare two dives of the same profile. One using the PADI air table and the other using my Dive Excel spreadsheet. The profile was 80 ft / 20 min, ascend to 50 ft / 20 min, ascend to the surface for a 2:35 hour SI. The spreadsheet's profile was calculated using a 60 fpm descent, 30 fpm ascent, GF: 100/100.

Using the table 20 min at 80 put me in group K which led to group R after 20 min at 50 ft with a RN of 36 minutes and ABT of 44 minutes. Group A was achieved after a 2:35 hour SI. The SI used going from 80 ft to 50 ft was 0:00 min.

Using the spreadsheet, after 20 min at 80 ft the NDL was 8, after 20 min at 50 ft the NDL was 28. After the 2:35 hour SI the NDL went up above 99 minutes and the GF ended up at 21. After the ascent to the surface the CTC was 5 with a HT of 27 minutes. I believe the table uses only one TC with a HT of 120 minutes.

I don't know what we can glean from this since using tables and computer software is like comparing apples and oranges.

 

[dmaziuk]

I’ve never been there.

It has swim-throughs. Including the one called Dolphin Den where dolphins get lost and drown. The vis in there is fine until the tourists raise silt, but they fail on both "see the exit" and "less than 25'" counts.

 

[tursiops]

Using the table 20 min at 80 put me in group K and group R after 20 min at 50 ft. Group A was achieved after a 2:35 hour SI. The SI used going from 80 ft to 50 ft was 0:00 min.

You lucked out. The RDP with your hack of zero time-to-surface when going from one level to the next is not in general valid. The eRDPml allows such calculations, and for the case you chose gives the same answer. It does not always work out that way.
For example, the correct calculation with the eRDPml says if you spend 20 mins at 80 ft, and then go to 50 ft, your new multi-level NDL is now only 34 mins more at 50 ft. So even though your procedure might make you think you could spend 44 mins at 50 ft, you actually only get 34 mins.

 

[John C. Ratliff]

What is 'short'? How long can a swim-through be before it does get into overhead/cavern territory?

Maybe this sequence from The Silent World by Cousteau, which shows Frëdërick Dumas exploring the Thistlegom shipwreck will give an example.

SeaRat

 

[Blackcrusader]

I would need the profiles of the other dives that same day to see if they could be planned with tables if we're going to do any comparison.

It's not so tricky if you follow recreational guidelines of never entering a ceiling. The point of NDLs is to have direct access to the surface at any point in the dive. Your example would not be acceptable for a recreational dive as long as you base it on GFhi of 75. If it turns out that I could plan this same dive within NDLs on the table using averages, it would be a good example of a potential problem with that practice.

A few pages back I posted same day profiles using GFhi 95