Thinking about Performance

[irie1029]

Ok here goes I am new to diving and Air consumptin is twice that of the experienced guys I dove with. To make a long story short... I use charts. The DM Stayed about 50' throughout dive I went to 68 for a 10 of the 35 minutes. Did 3 min stop at 15. I was almost at Mandatory stop (according to chart). The air integrated computer on the reg set console I borrowed said I was at group "G". Would a computer give me that much more "bottom" time? I did consume 2800 psi and by the way NOT in the BC i am now weighted pretty good. My breathing literally sucks. I know how to work on that as the DM gave me pointers.... So to reiterate my question is it acceptable to you manage your dive plan based on the computer? BTW the other guy diving solo was at easy 75 for twice as long as I was but used 1/2 the air he had to be beyond the chart right? Or is it the fact he used half the air so has half the nitrogene issue?

 

[Jimmer]

When you plan a dive based on dive tables, the tables assume you're going to your max depth and staying there for the entire dive. When you use a computer, it tracks your actual depth and nitrogen uptake, which is why your computer will tell you that you have more bottom time left, when the table says you're done. Nitrogen uptake is not based on your breathing rate at all, so even if he was breathing slower than you, he'd still absorb the same nitrogen if you were on the same profile the entire time. He may have been on Nitrox, which would explain why he seemed to be over the table limits.

I hope this helps,
Jim

 

[ditch-diver]

Hi irie.., I'll throw my $0.02 worth in.

I assume by 'charts' you are referring to dive tables and you are comparing your bottom times with your tables as opposed to the computer you were using.

When I got my first computer many moons ago, I did what you did.., sort of did both tables and the computer at the same time. Over time, I learned to trust my computer and now I feel perfectly safe planning a dive based on my computer profile.

The only time I use tables now are for work dives and that is because I have to.

There is an old saying (not that old but I like using it anyway) "You can't suck and blow at the same time" Don't mix yourself up trying to use both tables and computer. If you plan a dive with your computer, go by that. If you plan it based on tables, use them, not both.

One thing I will say is make sure you have a contingency plan in place for if your computer craps out during the dive. If no deco..., we normally plan for an immediate termination of the dive, with a 5 minute SS at 15'.

And to answer the second part of your question.., yes they do give you that much more bottom time. With the constant monitoring of depth, it provides a more accurate dive profile than your tables do, where your deepest is your depth. The computer takes into account all that time you were not at you max depth.., and adjusts your nitrogen loading accordingly.

They are like everything else..., a tool in the tool box. Use it well and it'll get the job done, miss use it and it'll cause you grief.

 

[spectrum]

First it is the time at depth and gas used that determines nitrogen loading. Rate of use is irrelevant.

A computer would not have helped that dive since you used 2800 PSI (of a 3000 PSI fill?) gas was the limting factor.

Since you dove tables the 70 foot depth was calculated for the whole dive when in reality it was only a portion. Calculating loading based on the actual multilevel profile of your dive is how the computer extends your NDL.

You should have some form of dive plan before going in. Knowing that it will be multilevel you will be relying to an extent on the computer. Having a plan gives you control in the event of a computer failure.

Dive often and be patient with yourself and your usage will drop.

Pete

 

[El Orans]

My breathing literally sucks. I know how to work on that as the DM gave me pointers....

Practice makes perfect.

My wife used to take the big tank, then she got comfortable diving. Now she usually ends up with more remaining pressure than me, using a smaller tank.

 

[scubadiver888]

Ok here goes I am new to diving and Air consumptin is twice that of the experienced guys I dove with. To make a long story short... I use charts. The DM Stayed about 50' throughout dive I went to 68 for a 10 of the 35 minutes. Did 3 min stop at 15. I was almost at Mandatory stop (according to chart). The air integrated computer on the reg set console I borrowed said I was at group "G". Would a computer give me that much more "bottom" time? I did consume 2800 psi and by the way NOT in the BC i am now weighted pretty good. My breathing literally sucks. I know how to work on that as the DM gave me pointers.... So to reiterate my question is it acceptable to you manage your dive plan based on the computer? BTW the other guy diving solo was at easy 75 for twice as long as I was but used 1/2 the air he had to be beyond the chart right? Or is it the fact he used half the air so has half the nitrogene issue?

Irie,

Don't stress yourself. If you are using 2800 PSI in a 35 minute dive then focus on conserving air. How much nitrogen loading you are doing is not a real concern. If you use a computer to calculate the nitrogen loading you will, typically, be in a lower pressure group then if you use your dive tables.

I just recently switched to a computer. My first dive with the thing was two weeks ago and it took a little getting used to. I am at a point where, on a two tank dive, I have to check my surface interval and wait for the second dive (had to sit around for 30 minutes just so I'd be in the proper pressure group for the second dive). If you are not in this situation, don't worry about dive tables versus computer. Stick with the dive tables and work on reducing your air consumption.

When you find yourself needing to wait between dives to get to the proper pressure group (according to the tables) then you want to start thinking about using a computer.

I cannot find my dive tables at the moment but my computer has a simulation mode. If I set it for 75 feet it tells me I have less than 30 safe minutes. My dive computer is fairly conservative. I'd guess that the diver you saw at 75 feet had a dive computer with a less conservative algorithm. His computer put him right at the limit. If his limiting factor is nitrogen loading and not air consumption this makes sense.

 

[battles2a5]

While your rate of breathing in itself may not determine nitrogen uptake, increased exertion will put you at greater risk for DCS. My guess is that you are overexerting yourself because you are either overweighted and kicking to stay bouyant or you are just not comfortable in the water yet (sculling, etc.). Either way, I would not recommend pushing the tables or your computer until your technique improves and your RMV comes down a bit. Three of the best things you can do to drop air consumption are 1) Use your BC instead of your legs for bouyancy, 2) stop using your hands and 3) frog kick. It is harder to mask issues 1 and 2 when you kick and glide instead of kick-kick-kick. It just takes a little time and practice.

 

[The Kraken]

Irie . . .

What you did is generally referred to as a "multiple level dive".

As mentioned previously, when planning a dive with the RDP (dive tables), the dive is considered to be a "square profile", that is, you descend to a predetermined depth and stay at that depth throughtout the whole dive. That is how you determine your ending pressure group.

Now, when diving a computer, the programs in the computer determine your times at respective depths and allow for the fact that you went deep, ascended to a shallower depth for a period, and then perhaps another shallow ascent to complete the dive.

The computer calculates for the differences in depths and times and adjusts your nitrogen loading accordingly.

The next time you make a dive like this, pay close attention to the bar graphs on the computer, if it has them, and you will see that your nitrogen loading bar graph will be reduced as you ascend in the water column.

Safe dives . . . . . .
. . . safer ascents !

PS:

As an afterthought . . .

If you know of anyone who has "The Wheel" dive planner and knows how to use it, they should be able to demonstrate how a "multi-level" dive works.

the K

 

[RonFrank]

Computer your dives, and dive your computer!

Dive computers are marvelous devices that take the guess work and mistakes out of dive execution from an NDL perspective. Most divers out there could not plan a multilevel dive to save their lives as most agencies don't train them to learn that skill. I learned on the wheel, so I learned multi-level dive planning.

I follow the computer as it does multi-level dive NDL calculations. IOW's it's not *planning* your dives, it's calculating your NDL based on what you have done on a dive. This is an important distinction.

As for air consumption, work on your buoyancy, and concentrate on taking very deep slow breaths both in and out. I find I normally take air in faster than I release it. IOW's I may breath in for 2~3 seconds, but then release it over 4~5 seconds. Do what is comfortable for you, but take deep breaths both in and out, and do so slowly. As you learn to use your lungs for buoyancy control, your breathing patterns will stabilize, and you will use less air. As you relax you will also use less air. The more comfortable you are in the water the less air you will use until you have more air in your tank at the end of the dive than you did at the beginning!

 

[wreckchick]

I'm going to nitpick for a tiny second because I think it's an important point that hasn't quite been hit yet, a dive computer is no more able to tell you what is actually physiologically happening in your body than a set of dive tables. The tables have been created based on algorithms that seem to mimic the way most people's bodies uptake nitrogen or end up being more conservative that what it actually happening.

Computers can be based on the same algorithm as the tables or some different ones that are out that all have some merit in the way they simulate on-gassing and off-gassing. When you are using a computer it is important to note that there is a huge variation in the level of conservatism between the different manufacturers and algorithms and some settings that the user can adjust. It is by looking at those factors that the user can determine their own safety factor and pick the right equipment and the right settings.

I think the recreational diver benefits greatly from the use of computers as long as everyone understands that it is merely a representation of what it happening, not reality and that pushing the computer is as bad as pushing the tables.

Rachel