dive to 300 ft
- Thread starter Crush
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
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
limeyx
Guest
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
JeffG
Contributor
limeyx
Guest
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.
JeffG
Contributor
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
lamont
Contributor
Discussion of helium fraction of gases and "best mix" split out to here:
http://www.scubaboard.com/forums/dir/396160-helium-fraction-standardized-gases.html
http://www.scubaboard.com/forums/dir/396160-helium-fraction-standardized-gases.html
Ragnar
Contributor
Slamfire
Contributor
*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:
- 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.
- 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'.
- 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.
- 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."
- 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.
- Post #47 - AJ gives a warning about breathing hypoxic gases at surface and refers to a near fatal incident.
- 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.
- 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.
Similar threads
