Teric NDL Plan

[mcpowell]

@KenGordon Here is an image of the dive profile:

I understand your post above, but I do wonder...you say NDL is a terrible indicator, but if I’m preparing for my next dive and I want to plan it, what should I use, if not the NDL dive planner?

 

[KenGordon]

Is your dive going to be square? Does the NDL planner plan for a square dive?

Scuba cliche no. 42 Plan the dive and dive the plan.

Before you did that 27 minute dive your planner said you could do 13 or 14 minutes (or whatever). Your actual plan wasn’t the one the NDL planner was talking about.

I expect you knew that you’d be doing a multi level dive and really it was more likely to be 27 minute 60ft dive with a minor excursion at the start to depth than a descend to 110, do 10 minutes and then ascend dive. Through experience (and mybe teaching) you know that having the deep bit at the start will extend your NDL time on the dive vs the deepest bit.

It is possible to plan such dives with tools such as MultiDeco, although that will not give you an NDL, but it isn’t at all ideal for this. If I am planning a one off deep dive wher I expect to be significantly shallower than the deepest part I might do a multi level plan but then what if I decide on the dive to spend all my time at the prop?

The most common way to actually plan these multilevel dives is to follow a guide or get a good briefing. Having dived the site before helps. If you know that there is nothing to see other than at the deep part (eg on a deep wreck) then the plan will be square, if the site is sloping or there is shallow stuff to see you will know you can extend your time. In the later case you will be playing it by ear or ‘riding your computer’. That will be ok so long as you have planned when you must ascend to remain safe in the face of failure. That is when proper gas planning is needed. If you know your ascent might need 100 bar then make sure you start ascending at the latest then. Leave some leeway on NDL in case of doing a slow ascent.

 

[mcpowell]

Ken,
I understand your comments better now. We were never planning to push the NDL, or need a decompression plan. In fact, we had planned for the entire dive to be no longer than 30 minutes. My entire line of questioning came from the observation that the Teric's NDL plan changed very little based on surface time, or tissue saturation. I had just had it in my mind there would be a larger variance.

As a matter of fact, this dive was almost an exact duplicate of one we had done about an hour earlier with the instructor and my son (who was completing his AOW). I had check my Teric's NDL plan on the first dive, just to make sure I was aware of the maximum time allowed at depth.

 

[John Dietz]

I ran the NDL planner before a dive, and it was giving me 17 minutes for 100ft. When I reached 100ft, the NDL value was 5min.

Next dive, surface interval of 2 hours, same 17min on the planner, I decided to change the GF conserv. level to low, and got the same 5min at 100ft.

I reached out to Shearwater, but the answer was kind of pale.

Does this ring a bell to anybody?

Thanks in advance.

 

[helgo]

Is your dive going to be square? Does the NDL planner plan for a square dive?

Scuba cliche no. 42 Plan the dive and dive the plan.

Before you did that 27 minute dive your planner said you could do 13 or 14 minutes (or whatever). Your actual plan wasn’t the one the NDL planner was talking about.

I expect you knew that you’d be doing a multi level dive and really it was more likely to be 27 minute 60ft dive with a minor excursion at the start to depth than a descend to 110, do 10 minutes and then ascend dive. Through experience (and mybe teaching) you know that having the deep bit at the start will extend your NDL time on the dive vs the deepest bit.

It is possible to plan such dives with tools such as MultiDeco, although that will not give you an NDL, but it isn’t at all ideal for this. If I am planning a one off deep dive wher I expect to be significantly shallower than the deepest part I might do a multi level plan but then what if I decide on the dive to spend all my time at the prop?

The most common way to actually plan these multilevel dives is to follow a guide or get a good briefing. Having dived the site before helps. If you know that there is nothing to see other than at the deep part (eg on a deep wreck) then the plan will be square, if the site is sloping or there is shallow stuff to see you will know you can extend your time. In the later case you will be playing it by ear or ‘riding your computer’. That will be ok so long as you have planned when you must ascend to remain safe in the face of failure. That is when proper gas planning is needed. If you know your ascent might need 100 bar then make sure you start ascending at the latest then. Leave some leeway on NDL in case of doing a slow ascent.

So, I am also having difficulty getting my Teric NDL plan to give me what I would find useful.
During the surface interval, I would like to know that i can, say, stay at 60 feet for, say 40minutes before i go down.
Yes, I realize that it is based theoretically on doing a square dive, which of course I am not going to do. I am going to do a gradual shallowing during the last 20minutes.
Therefore I should be WELL below that theoretical NDL limit the Teric is giving me, is that not right?

The other problem, as per the Teric manual, it gives you the folllowing:

"
The results are a list of depths,
along with the NDL time at
that depth and the best of the
programmed gases to use at that
depth. Only programmed gases are
used."

Well, I have like 6 pre-programmed gases.
But I want the NDL planner default to be the last used gas, with perhaps one click required to confirm it.
see attached picture, I would like the ability to indicate which gas I want the NDL planner to run on, but there seems to be no way to do that.


Needing some help please to clarify?

PS: I should add I know the sites I dive well, and how deep they are etc. So the difference it makes is in how long to wait at the surface?

 

[KenGordon]

So, I am also having difficulty getting my Teric NDL plan to give me what I would find useful.
During the surface interval, I would like to know that i can, say, stay at 60 feet for, say 40minutes before i go down.
Yes, I realize that it is based theoretically on doing a square dive, which of course I am not going to do. I am going to do a gradual shallowing during the last 20minutes.
Therefore I should be WELL below that theoretical NDL limit the Teric is giving me, is that not right?

The other problem, as per the Teric manual, it gives you the folllowing:

"
The results are a list of depths,
along with the NDL time at
that depth and the best of the
programmed gases to use at that
depth. Only programmed gases are
used."

Well, I have like 6 pre-programmed gases.
But I want the NDL planner default to be the last used gas, with perhaps one click required to confirm it.
see attached picture, I would like the ability to indicate which gas I want the NDL planner to run on, but there seems to be no way to do that.


Needing some help please to clarify?

PS: I should add I know the sites I dive well, and how deep they are etc. So the difference it makes is in how long to wait at the surface?

Read this Only Enable (Turn On) Gases That You Will Actually Use on a Dive - Shearwater Research
Gases set on the computer can be on or off. If on they then in the water can be selected (the one you are breathing) or not (carried, like deco gas yet to be used or bottom gas after a switch to deco gas)

As to your planning question, that is what experience tells you. You understand that a longer SI means a longer NDL for your next dive and if you remember the ratio between what the planner claims and your actual dives you could guess. What I would really do is plan my day to have as long an SI, up to a couple of hours, as works so maximising my chances of a decent second dive.

The Suunto DM5 logging and planning software can plan a dive following a previous one based on the actual dives done but it needs a laptop and is a faff.

MultiDeco etc can also plan two dives with whatever SI you like but you need to enter the profiles as a multi level dive, again likely a faff.

What would you pay for a planning feature “when can I do the same dive as the last again?”

 

[helgo]

Read this Only Enable (Turn On) Gases That You Will Actually Use on a Dive - Shearwater Research
Gases set on the computer can be on or off. If on they then in the water can be selected (the one you are breathing) or not (carried, like deco gas yet to be used or bottom gas after a switch to deco gas)

As to your planning question, that is what experience tells you. You understand that a longer SI means a longer NDL for your next dive and if you remember the ratio between what the planner claims and your actual dives you could guess. What I would really do is plan my day to have as long an SI, up to a couple of hours, as works so maximising my chances of a decent second dive.

The Suunto DM5 logging and planning software can plan a dive following a previous one based on the actual dives done but it needs a laptop and is a faff.

MultiDeco etc can also plan two dives with whatever SI you like but you need to enter the profiles as a multi level dive, again likely a faff.

What would you pay for a planning feature “when can I do the same dive as the last again?”

Yes, I did think I may have to delete some of my programmed gases...but it is convenient to have 31%, 32% and 33% all ready to go, cause it is a quick switch when you analyze the tank.
Wasn't aware they can be switched OFF, so did that now.
Yes, now the NDL planner is forced to use the 32% and solves that issue.

I would pay $99 for such a feature, but would need it to be on the Teric.

 

[inquis]

Therefore I should be WELL below that theoretical NDL limit the Teric is giving me, is that not right?

Right. Cutting the corner off the square profile (leaving the bottom before NDL goes to near 0) introduces conservatism.

You've probably noticed NDL typically increases with ascent, but there is a fairly slow rate to "shallow up" at which NDL stays about the same. This is called "riding NDL". (That rate is also slower as depth decreases.)

With a pre-dive NDL of 40 mins where you actually leave after 20 mins, you can ride that 20 min (remaining) NDL. At some point you'll be shallow enough that gas will limit your dive. Topography/interest may also limit you.

Hopefully it's clear that riding NDL at 1 minute remaining is riskier than 20 mins remaining because of the increased tissue loading. Personal call on how close to ride it.

ETA: typically the term "riding NDL" has a negative connotation, under the assumption the remaining time is near 0.

 

[inquis]

I ran the NDL planner before a dive, and it was giving me 17 minutes for 100ft. When I reached 100ft, the NDL value was 5min.

You may have inadvertently had the planner set for some time in the future rather than "now". Or possibly you made a slower descent -- it assumes 60 ft/min, which is pretty fast.

 

[tursiops]

NDL is a terrible indicatior.

It is a perfectly good indicator so long as you don't try and redfine NDL to mean something it is not.
Yes, it is for a square profile. Like tables.
Yes, it assumes a particualar descent and ascent speed. Like tables, even computer-generated tables where you have to specify your descent and ascent speeds.