cave profiles..

Hi guys and girls...

I am not a tech diver and there are no caves in Nova Scotia. That said, I was on the way home from work today, thinking about hitting the ocean this weekend, if I can get through the snow... and this came up..

Do you folks end up with a lot of sawtooth profiles diving caves? I don't suppose the caves tend to naturally slope down and up in a diver friendly manner..? You must have to plan your routes to account for this.

If this is a bonehead question.... I apologize, caves fascinate me, I would love to try it someday. For now I stick to the North Atlantic...thanks in advance for any responses.... dive safe folks...

chris

Some cave systems will have you going up and down some. Some more than others. Some sytems are very "diver friendly" as far as profiles go. We do have to plan where we are going to make our deco stops but it's usually not that difficult. By the way, sawtooth profiles and making the deepest dive first si not as serious as it used to be, according to some?! Dive Safe-Dive Alot-M

nalfein:

Hi guys and girls...

I am not a tech diver and there are no caves in Nova Scotia. That said, I was on the way home from work today, thinking about hitting the ocean this weekend, if I can get through the snow... and this came up..

Do you folks end up with a lot of sawtooth profiles diving caves? I don't suppose the caves tend to naturally slope down and up in a diver friendly manner..? You must have to plan your routes to account for this.

If this is a bonehead question.... I apologize, caves fascinate me, I would love to try it someday. For now I stick to the North Atlantic...thanks in advance for any responses.... dive safe folks...

chris

Click to expand...

It's not a boneheaded question at all.

Obviously caves vary from one to the next, so it's hard to give a generic answer. And obviously you are at the mercy of the cave in regard to profile.

I.E. you can't plan to spend xx minutes at yy feet then another zz minutes at ww feet.

Generally, the cave systems I've dove tend to get progressively deeper as you penetrate. One thing that you have to be careful with in cave is because there is usually a "hard bottom" and a "hard ceiling" your perception of depth can easily be fooled. What I mean is, you cant look up and see a 100 feet of water above you, or 100 feet below you and just estimate your position in the water column. Therefore it you have to pay a little more attention til you develop the ability naturally.

This is also a good argument for progressive penetration into a cave system. That way you become familiar with it and know the spots where it gets deeper and possibly shallower, and you can plan your bottom mix, and deco gasses and stops accordingly.

There are some good scenarios regarding this in the NSS Cave Diving Manual in the chapter dealing with decompression procedures. Basically what it states is that there are times when it is possible to find yourself need to do a decompression stop deeper than it is possible for you to get in a cave and that this type of scenario should be avoided.

In general though, caves do not produce a terrible amount of sawtooth profiles and proper training and technique teach you how to best plan for and deal with those occurences when it does happen.

Hope that helps.

Thanks Michael, thanks John...... appreciate the feedback.

I'd never really considered the possibility of incurring an obligation where you couldn't get enough depth to make your stop, that's grim... The manual sounds like a great read... I should pick up a copy.

have a great weekend...... on the bottom I hope

chris

nalfein:

Thanks Michael, thanks John...... appreciate the feedback.

I'd never really considered the possibility of incurring an obligation where you couldn't get enough depth to make your stop, that's grim... The manual sounds like a great read... I should pick up a copy.

have a great weekend...... on the bottom I hope

chris

Click to expand...

I'll post a more detailed example sometime later (possibly this weekend).

Good question !


http://www.ekpp.de/images/02-doux-profile.gif

shows a fairly easy profile, since the dive is long. All depths are in meters.

http://www.ekpp.de/projects/gourneyras03_07/survey_G.html
shows are more "fun" profile, going down from 330ft to around 150ft.

We usually run "average depths" for the total decotime and "maximum depths" to get the stop-depth for the deep-stops (if they are not already done on the way out)

Michael

For the "imperial" thinkers i have uploaded my vyper profiles:
http://www.ekpp.de/micha/coly03_ft.jpg
Is the coly 2003

http://www.ekpp.de/micha/gour03_ft.jpg
Is the Gourneyras

I like the vyper for that ! The only drawback is that it stops recording after 999 Minutes

Michael

Cave Diver:

There are some good scenarios regarding this in the NSS Cave Diving Manual in the chapter dealing with decompression procedures. Basically what it states is that there are times when it is possible to find yourself need to do a decompression stop deeper than it is possible for you to get in a cave and that this type of scenario should be avoided.

Hope that helps.

Click to expand...

I agree the NSS example of the impossible profile is an intriguing one, but I am yet to see a good explanation, diagram or dive profile of it. Has anyone seen one?

It doesnt calculate, at least in my brain, how you can generate a stop that is deeper than your present depth, unless you have already broken a decompression ceiling.

If you have a very zigzag profile, I can see how you may need to start decompressing, then descend during the exit due to the geometry of the passage, continue to add to your bottom time, then have to start a second sequence of decompression to exit.

In my mind, it is however impossible to get a tissue loading greater than the depth you are at (assuming you did the first set of deco correctly) therefore it s impossible to become super saturated while maintaining a constant depth.

If you have supersaturated tissues from the first part of the profile, that have not exceeded their m-value, or have decompressed them to below the m-value, they will continue to off gas in those tissues. The tissues that are not yet saturated may continue to on gas, but still cant generate a stop deeper than you are, as once they reach the loading of the depth you are at, they stop on gassing.

I think Im going to have to dust the NSS manual off and look this up again!

If anyone has a link or diagram, post it before my head explodes.

cancun mark:

I agree the NSS example of the impossible profile is an intriguing one, but I am yet to see a good explanation, diagram or dive profile of it. Has anyone seen one?

It doesnt calculate, at least in my brain, how you can generate a stop that is deeper than your present depth, unless you have already broken a decompression ceiling.

If you have a very zigzag profile, I can see how you may need to start decompressing, then descend during the exit due to the geometry of the passage, continue to add to your bottom time, then have to start a second sequence of decompression to exit.

In my mind, it is however impossible to get a tissue loading greater than the depth you are at (assuming you did the first set of deco correctly) therefore it s impossible to become super saturated while maintaining a constant depth.

If you have supersaturated tissues from the first part of the profile, that have not exceeded their m-value, or have decompressed them to below the m-value, they will continue to off gas in those tissues. The tissues that are not yet saturated may continue to on gas, but still cant generate a stop deeper than you are, as once they reach the loading of the depth you are at, they stop on gassing.

I think Im going to have to dust the NSS manual off and look this up again!

If anyone has a link or diagram, post it before my head explodes.

Click to expand...

If you calculate decompression using tables based on max depth and total time you can end up with a first stop depth that's deeper than your current depth. For insance if you are at your max depth for only a short time like if the cave runs at 60 or 80 ft and drops down to 180. Maybe you drop down deep for only a couple of minutes. You're back up in the shallow section when you start you're ascent...except the tables tell you that you're first stop is deeper.

I made up those depths without any tables in front of me so it might not works with those depths but you get the idea.

In reality what we would do if you aren't using a computer is to plan it as a multilevel dive using decompression software or calculate decompression based on a "profile depth" which is less than max depth but more than the shallow depth (some would use an average but it doesn't have to be)

cancun mark:

I agree the NSS example of the impossible profile is an intriguing one, but I am yet to see a good explanation, diagram or dive profile of it. Has anyone seen one?

It doesnt calculate, at least in my brain, how you can generate a stop that is deeper than your present depth, unless you have already broken a decompression ceiling.

Click to expand...

The problem states that you need a 20' stop by the time you reach point A. By the time you swim a considerable distance at a depth of 25' to point B, you've now spent a signficant time below your original stop. This in turn pushes you into a deco schedule calling for a 30' stop, but there is no place deep enough to do it.

One solution would be using advanced decompression techniques and carrying a deco bottle with a higher percent of 02, which would wipe out or greatly reduce your deco obligation. This wasnt addressed in the chapter however, because the scenario was under basic decompression technique.