Insta-buddy DECO Diver: What’s NDL?

[Saboteur]

I wonder too about new divers that aren’t taught tables then dive with out personal computers. They either rent computers they don’t understand or worse yet dive based on another’s computer.

In my observation on dive OP's, customers that are renting are given a basic overview of that computer. But I've seen one diver who didn't get it or ignored the NDL.

 

[uncfnp]

It seems to me that without tables the whole concept of NDL becomes even more abstract. Kind of like taking two apples and “adding” two more apples and then seeing four apples vs punching 2 + 2 into a calculator and getting 4. With the calculator (and computer) its more *just a number* without understanding the concept behind it.

 

[Eric Sedletzky]

As long as we are being honest, a signal for "what's your pressure?" was not covered in my training.

It was in mine, PADI 1998 OW.
No computers taught, tables at that time. They taught us to ask each others tank pressure by pointing to our SPG’s, and holding up fingers for numbers and making 0’s with our thumbs and forefingers. Still do it this way today.

 

[Storker]

They taught us to ask each others tank pressure by pointing to our SPG’s, and holding up fingers for numbers and making 0’s with our thumbs and forefingers.

This is why it may be a good idea to go over basic hand signals with a new buddy.

We don't bother with zeros, all pressures are in tens of bar by convention. And since more than a few around here use three-fingers mittens, there's no clear distinction between "three" and "five", and you just can't say "four". So we round the numbers as appropriate, and we use a clenched fist similar to "hold" for five.

If you ask me about my pressure, be it by pointing at me and at your SPG, or using the PADI signal "forefinger and long finger against the palm of the other hand", you'll get a number showing the tens of bar I have. Except if I have some 140- ish or 90- ish bar, then I might round up to 150/100 or down to 130/80 as I see appropriate if I'm wearing three-fingers. 120 bar will be "fist", "fist", "two". Something like 105 bar is easily rounded to 100.

It's kind of fascinating how much you can convey with a few simple hand signs. On a rather recent dive, I swam over to my buddy and did "point at me", "two fingers against palm", "fist", "fist", "flat palm ascending one step". What I was saying with that was "I've got only about a hundred bar left, so I'm going a bit shallower to preserve gas so we can spend about the amount of time underwater that we agreed on". But it only works if your buddy is reasonably squared away and that you either know each other, have a similar background as yourself or you've have had a decent pre-dive chat.

 

[Eric Sedletzky]

This is why it may be a good idea to go over basic hand signals with a new buddy.

We don't bother with zeros, all pressures are in tens of bar by convention. And since more than a few around here use three-fingers mittens, there's no clear distinction between "three" and "five", and you just can't say "four". So we round the numbers as appropriate, and we use a clenched fist similar to "hold" for five.

If you ask me about my pressure, be it by pointing at me and at your SPG, or using the PADI signal "forefinger and long finger against the palm of the other hand", you'll get a number showing the tens of bar I have. Except if I have some 140- ish or 90- ish bar, then I might round up to 150/100 or down to 130/80 as I see appropriate if I'm wearing three-fingers. 120 bar will be "fist", "fist", "two". Something like 105 bar is easily rounded to 100.

It's kind of fascinating how much you can convey with a few simple hand signs. On a rather recent dive, I swam over to my buddy and did "point at me", "two fingers against palm", "fist", "fist", "flat palm ascending one step". What I was saying with that was "I've got only about a hundred bar left, so I'm going a bit shallower to preserve gas so we can spend about the amount of time underwater that we agreed on". But it only works if your buddy is reasonably squared away and that you either know each other, have a similar background as yourself or you've have had a decent pre-dive chat.

We don’t use bar around here or three finger mitts, but when I go to Sweden next to visit family I’ll plan a trip to Norway to go diving and you can show me how you guys do it.

 

[Storker]

We don’t use bar around here or three finger mitts

My point exactly. Different sites have different conditions which may have different demands. And local conditions might well affect what's normal practice. So if you're traveling out of town to dive, it might be a good idea to have a somewhat longer pre-dive chat to ensure that we're all on the same page.

 

[Saboteur]

Only one dive OP of four I've used in the Caribbean mentions watching your NDL during the dive briefing. It is as important as gas supply (which is always covered). Given that there are users of rental computers who may not dive often or even those with their own computer that are rusty on it it is probably worth mentioning at briefings.

 

[rabe]

The diver is ultimately responsible. A certified OW diver should have a basic understanding of dive theory, dive planning, risking avoidance and proper equipment usage, assembly and function. If in doubt, don’t dive. How many divers are thumbing dives due to ignorance?

I don't know...
You don't know what you don't know, therefore if the instructor didn't teach, is not the diver fault.
However, I think it is also diver responsibility to instruct himself.

 

[Manatee Diver]

Only one dive OP of four I've used in the Caribbean mentions watching your NDL during the dive briefing. It is as important as gas supply (which is always covered). Given that there are users of rental computers who may not dive often or even those with their own computer that are rusty on it it is probably worth mentioning at briefings.

The Caribbean DMs seem like they are pretty good about planning the dives to avoid deco as a worry for all but the deepest dive. Going back through my dive log and I see the closest I got to deco was 22 minutes during my recently trip to Mexico. Of course I did miss the deep dive day, so my maximum depth was 85 feet.

 

[Bob DBF]

My son just finished PADI OW training and he was taught tables, but not computers. I found that odd since I thought tables are no longer taught as well.

I think it's an instructor choice, but with the predominance of computers in diving it has shifted to the dive computer training. Also it's another sale, "since you need one anyway, buy it with your mask, fins, and snorkel".


Bob