First Dive Trip Without Instructor - Need to Rent Gear & Help Planning

[MichaelMc]

I am mixing up narcosis and toxicity, for sure.

it's something that unfortunately very few instructors truly understand and the agencies don't do much to help by trying to dumb it down.

For instructors to not know narcosis from toxicity is very depressing. It's not a difficult distinction, and near the top of the short list of things in that class. Like the first sentence "Nitrox can reduce nitrogen loading, but does not reduce narcosis, and adds risk of oxygen toxicity. We'll talk more about each of those.'

CavernFrog, The Navy dive manual is a good source, and it sounds as if you should redo a few of your classes with better instructors.

 

[RIHappyDiver]

Ok, @boulderjohn, I shot off my big mouth and now it’s time for the test. Either I failed miserably, or this was a bit of a trick question, and an example of why computers give us even more extend time than nitrox (please, Lord, don’t let it be “failed miserably”). Per the PADI DSAT tables, you would be sitting out for the rest of the day after the first dive of each day due to surpassed NDLs. Day one/dive one, your EAD is 80’, NDL is 30’, day two/dive one, EAD is 80’, NDL is 30’, day three/dive one, EAD is 63, NDL is 40’.

So, on these dives I will guess that shortly after hitting the depths stated, you ascended to shallower waters, decreasing your NDL, and enjoyed the rest of the time.

Ok, I’m ready for the critique. (Please don’t let it be “failed miserably”!)

Erik

 

[boulderjohn]

Ok, @boulderjohn, I shot off my big mouth and now it’s time for the test. Either I failed miserably, or this was a bit of a trick question, and an example of why computers give us even more extend time than nitrox (please, Lord, don’t let it be “failed miserably”). Per the PADI DSAT tables, you would be sitting out for the rest of the day after the first dive of each day due to surpassed NDLs. Day one/dive one, your EAD is 80’, NDL is 30’, day two/dive one, EAD is 80’, NDL is 30’, day three/dive one, EAD is 63, NDL is 40’.

So, on these dives I will guess that shortly after hitting the depths stated, you ascended to shallower waters, decreasing your NDL, and enjoyed the rest of the time.

Ok, I’m ready for the critique. (Please don’t let it be “failed miserably”!)

Erik

Like probably 90% of the dives done by recreational divers, these were multi-level dives. Multi-level dives have a maximum depth, of course, but most of the dive is spent well above that maximum. A computer tracks that easily and constantly adjusts your NDL, but dive tables are based on maximum depth only. Thus, for the vast majority of dives done with a computer, you cannot accurately switch to tables if your computer stops working.

It is not that you did not know how to do it; it is that it cannot be done.

 

[boulderjohn]

I started diving just about 20 years ago, and my first trip after certification was to Cozumel, where all dives are led by a DM. After my first multi-level dive, we all sat on the boat having a surface interval. I pulled out my dive log and my dive tables. I looked at my depth gauge and noted the time I had recorded on my dive watch. I was preparing to plan the next dive, as I had just been taught, but as was true in the cases above, according to the tables, I was already long dead and would not be doing any more diving that day. I was puzzled. I then looked up and saw that everyone was looking at me, barely stifling the laughter. One of them pointed at my tables and said, "It makes a decent Frisbee."

That was 20 years ago. It is still the only time I have ever seen anyone attempt to plan a recreational dive with tables outside of a class setting.

 

[RIHappyDiver]

Like probably 90% of the dives done by recreational divers, these were multi-level dives. Multi-level dives have a maximum depth, of course, but most of the dive is spent well above that maximum. A computer tracks that easily and constantly adjusts your NDL, but dive tables are based on maximum depth only. Thus, for the vast majority of dives done with a computer, you cannot accurately switch to tables if your computer stops working.

You're absolutely right, and it was a bad example to use to show my original point (which is argued on here all the time) that it's not always agency, it's sometimes the instructor. @azstinger11 felt his PADI class was too basic in it's scope, whereas I felt I learned a lot in my PADI class. I probably used the tables as an example because when I started diving 39 years ago they were what you had, so you used them. I don't any more with computers, but I still practice them because it makes the critical numbers more real to me.

Erik

 

[Neilwood]

This is another example of it’s the instructor, not the agency. My instructor taught the computer settings but focused a lot on tables and calculating repetitive dives on worksheets. I have no doubt that if my computer goes belly up, I can figure out my next dive with my tables. Haven’t had to, but I keep practicing just in case.

Agree with the sentiment -on my Nitrox course the instructor spent a good while on the why and how of PPO2, MOD etc so that we all would understand it (and can work them out if need be).

As @boulderjohn has demonstrated though, should the computer fail (and you don't have a back up) I would sit the next dive because, as he says, on 90% of recreational dives you will be multi depth and likely so far off the table that it wouldn't work.

Recreational dive planning/NDL's only work with either tables OR computers unless you are on square profiles

 

[CavernFrog]

This is giving me an idea for some kind of like... keychain or bracelet or something made of a material that changes colors with sustained pressure changes and correlates roughly with one's nitrogen absorption.

 

[tursiops]

This is giving me an idea for some kind of like... keychain or bracelet or something made of a material that changes colors with sustained pressure changes and correlates roughly with one's nitrogen absorption.

Why? The first decometers were like this --the "bendomatic" SOS -- and not everybody using one got bent. How is your bracelet better than today's dive computers?

 

[halocline]

I am open to re-doing any of my certifications. I enjoyed the training and studying and would love to do it all over again.

What technical dive training do you have, if you don't mind me asking? What agency did you take cavern class with?

Edit: I saw that later in the thread you mentioned PADI cavern. So that's probably not a very good course, and your questions about the guideline indicate very little understanding of it.

Another question, how many OW dives do you have and how long have you been certified?

 

[tbone1004]

This is giving me an idea for some kind of like... keychain or bracelet or something made of a material that changes colors with sustained pressure changes and correlates roughly with one's nitrogen absorption.

to correspond with the most common algorithms on dive computers, you'd need 16 colors. Keep a spare computer if you're that concerned