dive to 300 ft

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Yeah, I have descended in reasonable conditions on 12/65 a few times with no ill effects (although it was annoying getting slammed in the face with surface chop on one dive as we tried to fix a reg leak)

for 10/70 I would almost certainly just breathe the 190 bottle on descent, not just to have something breathable but to save the bottom gas a little too (depending on how much of the 190 bottle you expect to use of course)

Having experienced the first symptoms of Hypoxia @ 6m on 12/65 I'm very wary of doing that now. It doesn't take much exertion for issues to start, and it's something that can be easily avoided.

Thanks
John
 
Interesting to see you guys skipping the 120 bottle. Something we've been considering here as well, as the min gas just starts to get insane with only a 120 bottle, but if you bring the 120 as well, it just seems to get into bottle hell.

Pretty much what we've been thinking about within our team. We're not yet doing 3 deco gas dives, but have run the numbers a few times now as we have some tempting potential wrecks below 250'. Decowise there doesn't seem to be much difference between 21/35 or 35/25, but other factors would make us choose 21/35 over 35/25, such as some leeway with min gas (though you can't really calculate min gas to 21/35 switch), getting on the gas earlier etc. Having both would only start making sense with extreme depth or BT.

It's not really a dive parameter, but I also do prefer to be left with an Al80 of 21/35 than 35/25 if blown out... :)

//LN
 
Having experienced the first symptoms of Hypoxia @ 6m on 12/65 I'm very wary of doing that now. It doesn't take much exertion for issues to start, and it's something that can be easily avoided.

Thanks
John

For sure. Another good reason to skip the 35/25 and bring the 190 bottle which I think makes a better travel gas for that kind of dive.
 
Pretty much what we've been thinking about within our team. We're not yet doing 3 deco gas dives, but have run the numbers a few times now as we have some tempting potential wrecks below 250'. Decowise there doesn't seem to be much difference between 21/35 or 35/25, but other factors would make us choose 21/35 over 35/25, such as some leeway with min gas (though you can't really calculate min gas to 21/35 switch), getting on the gas earlier etc. Having both would only start making sense with extreme depth or BT.

It's not really a dive parameter, but I also do prefer to be left with an Al80 of 21/35 than 35/25 if blown out... :)

//LN

Either way make sure that you have enough back-gas to deal with a loss of that deep deco gas. You will find that it doesn't take much deco to drain that 21/35 bottle and you'll need to think about what to do if you have an issue with that bottle.

J
 
Interesting to see you guys skipping the 120 bottle. Something we've been considering here as well, as the min gas just starts to get insane with only a 120 bottle, but if you bring the 120 as well, it just seems to get into bottle hell.
Once you get into this bottle hell is when its a good time for a support diver.

Once you start having to deal with moving bottles off/on a leash brings in the possibility of dropped bottles. (I have seen 3...mind you, all from the same diver)
 
Once you get into this bottle hell is when its a good time for a support diver.

Once you start having to deal with moving bottles off/on a leash brings in the possibility of dropped bottles. (I have seen 3...mind you, all from the same diver)

I move bottles all the time, without incident. Maybe that diver needs some new (less slippery :) gloves.

3 bottles is one thing.

Once you add a bottom stage + 3 deco then things start to look like the max I really want to do without a lot of support.

Unfortunately most of our diving is "fun" and not project-based so bringing support divers is just not usually practical.
 
No, its because Scubaboard is blocked at work, so I don't spend that much time on it. Plus...maybe its my age, but I find it tougher and tougher dealing with the numbnuts on SB lol
 
So what is proper DIR procedure for a dive like this? Breath hold initial descent, one or two breaths of hypoxic 10/70, or using 35/25 as a travel mix?

Breath hold......Seriously? Do you have any GUE training at all? Seems to me you shouldn't be concerned about how to dive to 300'.
 
Breath hold......Seriously? Do you have any GUE training at all? Seems to me you shouldn't be concerned about how to dive to 300'.
*deeeep sigh* *serenity now...* I do not know how many times I've posted "I'm not DIR trained" right before I begin contributing to a thread in this forum. This thread was no exception -- see post #27. I've never pretended to be GUE, or whatever other DIR flavor of choice...

As for the breath holding, let me try to spell it out to you as to how this comment came to be:
  1. Post #27 - I present a 300 ft dive with a 10 min bottom time using std gases (OPs depth and bottom time) and request divers who are indeed DIR trained to critique the profile.
  2. Post #29 - Brian Nadwidny kindly replies and among his comments he mentions that he "would not use a 'travel gas'". The "travel gas" that I presented in my sample profile is simply 35/25 which would be used for descending the first 100'.
  3. Post #31 - I ask Brian if he uses the hypoxic mix for a minute or less while he gets to 2 ATAs in order to avoid doing one extra gas switch.
  4. Post #35 - Brian says, "You don't need to get to 2 ATAs for a 10/70 to not be hypoxic. More like 1.5 which takes about 10 seconds or less." Ragnar, do you think you could hold your breath for 10 secs or less? Brian further clarifies, "Now then if it was really snotty out and we thought that we needed to have a reg in our mouth for the surface part we would splash in breathing off our 70 bottle or our 120. But this was rarely the case."
  5. Post #45 - I make the first mention of a "breath holding" descent when I say, "It's not a big deal to hold your breath for a minute, it would be less of a big deal to breath 10% from surface to 1.6 ATAs. I gave 2 ATA initally because it's an easy target -- 33 ft, 10 m or 0.2 ppO2 -- which is well within normoxic." Ragnar, please note the comprehensive context of my breath holding comment. Readers in general please note that I am not recommending that you hold your breath at any time while scuba diving and nobody else in this thread has. I personally have never descended on scuba doing a breath hold.
  6. Post #47 - AJ gives a warning about breathing hypoxic gases at surface and refers to a near fatal incident.
  7. Post #48 - gsk3 clarifies that breathing hypoxic mixes at surface could be even more dangerous than holding your breath. He also clarifies that many people do breath hypoxic mixes at the surface for a brief period of time while descending.
  8. Post #50 - I reply to AJ and gsk3 telling them I understand what they say. It is in this post that I wrote the question that you found, shall we say, distasteful. Again, Ragnar, look at the question within the comprehensive context before you start attempting to take the attribution to tell me what I should or should not be doing -- what I do or do not is of no concern to you. Also note that at no time am I even trying to give advice to other people. I am no DIR diver and all I'm doing here is asking questions in a genuine attempt to learn more.
 
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