last stop at 3 or 6m?

[Valery]

thanks guys for all your input its becoming a litle clearer now. Keep giving your opinion

 

[Bubbletrubble]

Well I'm talking about both tech and recr diving.

I know that on O2 I should stay at 6m.

Now decoing with 50% or with air (most of our dive are small deco with air) and knowing that I can set my computer last stop at 3 or 6m, should I care about the gradient and do my last stop at 3m? My instructor state that you off gaz better at 6m while another 1 state that your not doing any good by staying at 6 and he can't find any good reason not to do my last stop at 3m, and that I'm doing no good in terms of off gasing by staying at 6m.

Still can't make up my mind on what's best for me.

@Valéry: Time-out. I'd like to caution you about trying to do too much too fast. It might be a good idea to gain more experience doing recreational-type dives (staying within NDLs) before doing deco dives. Your SB profile indicates 25 - 49 dives if I'm not mistaken.

 

[Diver0001]

I know there might not be a correct answer for this question but I'd like to have an instructor point of view on the following:

Why should I set 6m for the last stop rather than 3m?
Well after speaking with my instructor he insistes that more and more tech diver are now doing there last stop at 6m. I told him that it must be because they are doing there last stop with O2, but he kept telling that it would be better for me to do my last stop at 6m even with air.

What do you think? Some argue that the 3m stop shouldn't be replaced with the 6m and other says that you off gas better at 6m so what's the real story???

Your last stop is at the surface. Everything else before that is just about how you get there.

Here's a thought: You can extend the 6m stop (or any other stops shallower than 6m) indefinitely.... If you can't choose between doing a stop at 6m or at 3m then do them both.

R..

 

[Valery]

I've done the adv nit course this winter which alows me to have up to 15min deco a ean50% (as you already know) and maybe in 1 or 2 weeks I'll start the deco procedure course.

Adv Nit has been the most difficult course I've taken so far, the instructor realy kicked my a$ during training with increadable exersise and triky things

 

[Rick Murchison]

If decoing on air or 50%, I believe the 10' stop is worthwhile.
If using 80%+, then the principle advantage of using 20' is in stopping potential bubble growth without any measurable penalty in off-gassing gradient.
Only downsides are increased oxygen exposure if you're already pushing that, and about 20% - 25% more deco gas consumption for the time you could spend at 10'.
Rick

 

[Trace Malinowski]

Your last stop is at the surface. Everything else before that is just about how you get there.

Here's a thought: You can extend the 6m stop (or any other stops shallower than 6m) indefinitely.... If you can't choose between doing a stop at 6m or at 3m then do them both.

R..

I agree. The last stop is at the surface and you can take advantage of keeping some hydrostatic pressure on your chest by taking time to relax and talk about the dive or debrief it. Cave divers tend to take more advantage of this stop because cave diving often means divers aren't rushed to get back on board the boat by the crew or the surface conditions. If time and conditions allow me to do a surface deco stop when boat diving, I'll hang on the tag line for 10 or 15 minutes.

An ascent is normally divided into 4 - 5 phases:

Bottom Phase - normal ascent rate usually at 30 feet per minute to get off the bottom and cease to "on gas."

Deep Stops - short stops that begin at about 75% of max depth or 80% of max ATA's to take advantage of the bubble model theory.

Intermediate Stops - incorporates 50% of the decompression in the mid-range of the ascent and takes into account bubble and dissolved gas theories and often takes advantage of the oxygen window effect with a gas switch.

Shallow Stops - the other 50% of the decompression time is performed with attention to the dissolved gas theory and will often take further advantage of the oxygen window with a second gas switch being performed at 6m.

Surface Deco Stop Option - 10 or more minutes spent with the torso still submerged.

I often will do the time required at 3m and 6m entirely at 6m. This is true especially if I am using oxygen as a deco gas. Whether I do this or not depends upon what I felt about the dive and how I feel during my ascent. If I feel really good about the dive profile, I may stop at 6m then 3m on schedule. If I feel I need to take more time at depth or feel I want to make sure I didn't close the full advantage of the O2 window too soon, I'll do all shallow stops at 20 feet. When I don't do a shallow gas switch, I tend to move to the 3m stop, but I may extend it to act as a hybrid between the last submerged stop and the surface deco stop. Even when I complete the time for the entire 6m and 3m stops at 6m, I may ascend to 3m on whatever gas I am breathing and further extend the curve. If I feel that the entire profile wasn't as clean as it could be, I may curve my time at 3m and the surface as if they should be part of the ascent plan. Last year, I surfaced from a dive feeling bent and went back down to perform emergency deco as if I had omitted my stops. It seemed to work.

Conditions may also play a role. If spring water is colder at 3m when cave diving than at 6m, I'll stay at 6m. As others mentioned, wave action, surge, and other surface conditions may see me adjusting my final stops based upon whatever is easy or safe.

When I do recreational diving, I incorporate deep stops at 50% of depth until I reach the shallow stops and then I usually do a 3 - 5 minute safety divided between 20 feet and 10 feet or all at 15 feet. Those just depend upon how I feel I should do it based upon the profile and the conditions.

Once I've satisfied the voodoo science of deco theory, then I turn to my gut instinct to plug any holes that may exist in the dam between theory and reality.

 

[ianr33]

If you are decoing on air then you will get out of the water faster doing the last stop at 10' . If you have a significant amount of deco to do it can make a big difference (although if you have that much deco to do air is not the best gas to be doing it on)

Sure you can do the last stop at 20' but unless there are good reasons to do so (big waves) it seems pointless to me.