Ascending without a dive computer

[divad]

I'm sure you could go without a car today.

I did it for 32 years, in lower Manhattan,...………….....AND I LIKED IT THAT WAY.

( and no, my eyes did not burn out of my skull and my hair did not catch on fire)

 

[barth]

There is no question that using tables is a very safe way to dive. People are writing as if simple safety were the only factor involved. If you want nothing but safety, stay in bed. I guarantee you will not get bent.

The reasons for using computers instead of tables involve things like the ability to do multi-level dives, adjust dive plans on the fly, etc.

I tried it again. Last week in Mexico I changed gauge mode to oc tech. I didn’t like it.

My no deco time was 99 minutes during the dive. Actually 99 means 99 or more. So I still had to do my own planning for a 3 hour cave dive.

During a 3 hour dive, my computer had a problem after 2 hours. I think the computer started up again and logged it as a new dive. The data of the first 2 hours of the dive was lost.. So I still had to do my own diveplanning.

Maybe one day when dives are deeper than dives I do now (51 meter) or dives are getting more complicated than a 3 hour cave dive, gauge mode + wetnotes and/or planning software on my iphone are not enough anymore.

When my grandfather was young, he went everywhere with a horse and buggy with no adverse affects, so I'm sure you could go without a car today.

Do you think he needs a navigationsystem when he is driving a car ? Or do you think he can drive without it and do his own route planning ?

 

[doctormike]

Standard ScubaBoard Exchange:

Poster X: "This piece of gear is great for diving because of the following reasons..."

Poster Y: "Oh, so you are saying that every diver NEEDS that piece of gear? I have done a lot of dives without it, and I survived"

 

[boulderjohn]

There is also a "minimum" ascent rate at which you are essentially making a multi level dive and not an ascent.

This shows a difference between diving with tables and computers.

Tables give you a bottom time that goes until your direct ascent to the surface. They assume you will then ascend at the planned rate. Ascend too slowly, and you have added bottom time. The tables will not be able to calculate that added time, so your numbers will not be valid. You may well have violated the NDLs during your dive without realizing it.

Computers will recognize your ascent rate and include that in calculations. As you ascend, your NDL changes, and the computer will continue to tell you how close you are to it throughout the dive.

 

[boulderjohn]

I tried it again. Last week in Mexico I changed gauge mode to oc tech. I didn’t like it.

My no deco time was 99 minutes during the dive. Actually 99 means 99 or more. So I still had to do my own planning for a 3 hour cave dive.

During a 3 hour dive, my computer had a problem after 2 hours. I think the computer started up again and logged it as a new dive. The data of the first 2 hours of the dive was lost.. So I still had to do my own diveplanning.

Maybe one day when dives are deeper than dives I do now (51 meter) or dives are getting more complicated than a 3 hour cave dive, gauge mode + wetnotes and/or planning software on my iphone are not enough anymore.

I really have no idea what you are talking about here. Your post has me baffled.

First of all, this thread is about a new diver in the Basic Diving forum, not a 3-hour cave dive. However, it looks to me as if basic scuba concepts apply anyway. I have done dives in caves in Mexico myself, and in many of them, you are shallow enough throughout the dive that there is no need to plan for any decompression planning, even during a 3 hour dive. On the PADI tables (which are conservative), the NDL for a dive 35 feet or shallower on air is about 3 1/2 hours. What planning is it that you need to do for such a dive?

In some of the caves there, a good reason for the computer to restart during the dive is that you actually got to the surface during a dive. In that case, your computer will treat it like a second dive with nearly no surface interval. Your previous data is not lost.

If that is not the reason for your computer starting over, then you had a mysterious computer error.

Do you think he needs a navigationsystem when he is driving a car ? Or do you think he can drive without it and do his own route planning ?

Again, I am baffled. What does navigation have to do with any of this?

 

[Photo Girl]

OP, ascending as slow as your smallest bubbles works fine.

OTOH, a basic dive computer is not expensive. Mine only cost $150. It also stores your dive data (i.e. depth, temp, time) that you can download onto your pc, which makes logging your dives a breeze. The dive log software shows a graphic dive profile, a great tool for monitoring improvement of your depth / buoyancy control.

I think once you see all the advantages, you will not want to dive without one.

BTW, I dive with the dive computer on one wrist and my watch and depth gauge on the other wrist. I still plan my dives using the table, as a backup. I also use the 120 rule as a sanity check.

 

[txgoose]

There is also a "minimum" ascent rate at which you are essentially making a multi level dive and not an ascent. The minimum ascent rate has not, to my knowledge, been the subject of research but if you play with deco models then you will probably conclude that if you are not ascending at at least 3m/min that you are still ongassing too much during the ascent.

(apologies if I snipped out relevant parts of your post) Can you explain this more? I am surprised that a person could have too slow an ascent rate. I understand that the tissues that on gas slower will off gas slower. But it seems like a _very_ slow ascent rate, with enough air (not tech gassing), should actually have a person reach the surface in equilibrium. And maybe this is more a discussion of the applicable sweet spot, vs my theoretical and admittedly impractical sweet spot. Anyway, a neat area of thought possibly better suited for a separate thread.

 

[boulderjohn]

Do you think he needs a navigationsystem when he is driving a car ? Or do you think he can drive without it and do his own route planning ?

I am going to take a wild guess as to what this might mean. I am going to guess that you are saying that some people dive in ways that don't require the advantages of a computer. In that case, I agree with you. If you want to be limited in your diving and not use those advantages, you are free to do so.

For example, you are free to dive the bottom time limits of a table rather than the extended limits of a multi-level dive. I did 3 dives in Palau on May 10, with roughly a 1 hour surface interval between the 1st and the 2nd and roughly a 1.5 hour interval between the 2nd and 3rd. Please calculate them on your dive tables of choice and tell me what limits I would have had following the 1st dive if I had chosen to use the tables instead. (All dives were done on EANx 32.)

First dive: 91 feet for 66 minutes.
Second dive: 87 feet for 70 minutes
Third dive: 96 feet for 63 minutes.

 

[boulderjohn]

(apologies if I snipped out relevant parts of your post) Can you explain this more? I am surprised that a person could have too slow an ascent rate. I understand that the tissues that on gas slower will off gas slower. But it seems like a _very_ slow ascent rate, with enough air (not tech gassing), should actually have a person reach the surface in equilibrium. And maybe this is more a discussion of the applicable sweet spot, vs my theoretical and admittedly impractical sweet spot. Anyway, a neat area of thought possibly better suited for a separate thread.

See my post #34 for more information.

You seem to be assuming that all tissues are off-gassing as you ascend. They are not. Tissues will on-gas as long as the pressure of nitrogen entering the body through the lungs is greater than the tissue pressure. Tissues will off-gas as soon as the pressure in the tissues is greater than the pressure in the gas entering the lungs.

Before you begin your ascent, some of the tissues (the faster ones) will have reached equilibrium--the tissue pressure is the same as the inspired gas pressure. When you ascend, the inspired gas pressure drops, so those tissues will now have greater pressure than the inspired gas, and those tissues will begin to off-gas.

Before you begin your ascent, some of the tissues (the slower ones) will NOT have reached equilibrium--the tissue pressure is still lower than the inspired gas pressure. When you ascend, the inspired gas pressure drops, but those tissues will still have lesser pressure than the inspired gas, and those tissues will continue to on-gas.

Those slower tissues will one-by-one reach equilibrium and then begin to off-gas as you ascend, but you will not be off-gassing in ALL tissues until you are on the surface.

 

[JackD342]

(apologies if I snipped out relevant parts of your post) Can you explain this more? I am surprised that a person could have too slow an ascent rate. I understand that the tissues that on gas slower will off gas slower. But it seems like a _very_ slow ascent rate, with enough air (not tech gassing), should actually have a person reach the surface in equilibrium. And maybe this is more a discussion of the applicable sweet spot, vs my theoretical and admittedly impractical sweet spot. Anyway, a neat area of thought possibly better suited for a separate thread.

Buried on the Mares site is a pretty good 5 page document on their algorithm that explains how you can continue tissue loading on that kind of dive profile.
http://docs.softwaremares.com/understanding a dive computer.pdf