LiteHedded
Contributor
and there was a little more to it than just backgas exploding at max pen
When thirds are not enough....
- Thread starter boulderjohn
- 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
and there was a little more to it than just backgas exploding at max pen
ucfdiver
Contributor
They were also narc'ed on deep air, and knew that there was a gas leak...just didn't solve it because each of them assumed the leak was coming from their buddy.
PfcAJ
Contributor
And underweighted...
It's easier to point out when thirds is enough. The only time I will allow thirds when I'm diving as part of the team is when there are 3 of us diving a system we are all familiar with and doesn't involve any major restrictions. It's not likely to have 2 separate gas failures on a single dive. And the way I see it is if 2 of us do have gas failures, we're dead anyway. Any other type of dive/team configuration requires more conservatism.
ucfdiver
Contributor
You wouldn't dive 1/3rds on swim dive with a team of two when the flow is up at LR/Devils/JB?
You wouldn't dive 1/3rds on swim dive with a team of two when the flow is up at LR/Devils/JB?
I don't mind diving 1/3's on any of those. But then again my normal dive buddy likes to do slow dives where we poke around and look at stuff so thirds doesn't really take us that far. A 1200 psi penetration in those will often result in a 200-300 psi exit as we prefer to take our time going in when we have the most gas, and when it's time to turn, we typically head straight out.
Someone doing dives that takes them further and will take longer to exit need to take that into consideration during gas planning.
The only time I'll dive thirds is when I'm diving in a cave. For internet diving, I religiously stick to 1/10ths. I write a post, then delete 9/10ths of it. Posting more than one tenth of what I write runs me into the risk of too much internet penetration also known as caring way too much about the internet and not enough about real life.
(on a serious note, how many people actually dive something more conservative than thirds at Peacock? I mean actually dive it, not just post that you dive it. And I mean full cave divers, not intro divers, even the intro divers that dive thirds because they think they are Big Cool People that are above the guidelines.)
(on a serious note, how many people actually dive something more conservative than thirds at Peacock? I mean actually dive it, not just post that you dive it. And I mean full cave divers, not intro divers, even the intro divers that dive thirds because they think they are Big Cool People that are above the guidelines.)
Going back to an earlier post:
If the non-breather diver has a catastrophic failure, then he goes on the 40 -- correct? Now that may not be enough gas but ONLY the buddy goes on the 40 since the 'breather diver has no issue.
OTOH, if the 'breather diver has an issue, he goes on the 40 and the OC guy still has full gas.
OTHER THAN 40 may not be enough, I don't see the issue. What am I missing?
I'm a newbie at this so please be kind:
If the non-breather diver has a catastrophic failure, then he goes on the 40 -- correct? Now that may not be enough gas but ONLY the buddy goes on the 40 since the 'breather diver has no issue.
OTOH, if the 'breather diver has an issue, he goes on the 40 and the OC guy still has full gas.
OTHER THAN 40 may not be enough, I don't see the issue. What am I missing?
Me.
I have not dive 1/3rds at Peacock, Hole-in-the-Wall, Twin, and everything I've ever done in MX (maybe 40 different systems).
The only place I have (ever) dove 1/3rds is swimming JB (not scootering). I have not been to Ginnie or any of the other high flow caves which are actually a rarity in the grand scheme of things, just like diving 1/3rds is.
ucfdiver
Contributor
Frankly, I'll dive 1/3rds even scootering in JB or Ginnie (I dive 0/3rds @ Little River because the cave sucks and isn't worth diving) with a UV26/Gavin, because it still allows you to exit the cave swimming with a reasonable SAC, and underestimation of the flow. So no one takes my post out of context, this doesn't apply during flood stage when abnormal flow exists.
There are specific tunnels where I don't dive 1/3rds at Peacock, but for the stuff that isn't tight, I'm fine with 1/3rds. If you want to amuse yourself, search for grand traverse reports, nearly everyone uses 1/3rds to do that. If you read past conversation (as well as an article about it in either nacd/nss journal) people basically admit to diving 1/3rds for that dive fairly often. Then in threads similar to this one, they later post that they drastically back off 1/3rds in no flow.
Specific examples of backing off 1/3rds would be diving 1/4s at Lafayette Blue while swimming, or reserving all of back gas while scootering there due to poor line conditions and lots of silt along with no flow, as well as severely degraded visibility if it rains during your dive. I also don't touch much back gas when scootering Hole in the Wall due to the restrictions which blow out easily, and you can't tow a buddy through. Wilson Springs is another example, because the line and viz aren't the best (video here). Royal Springs requires heavy reserves as well due to there being 3 parallel guidelines, of which only one goes to your primary reel, and having to feel your way out of the cave. A few of the caves on the Wacissa River demand tons of reserve, simply because the line conditions and peculation are such unknown variables that you can't really calculate what's "safe".
It's quite rare that I back slightly off 1/3rds. Usually if I feel 1/3rds is unsafe, it's because of a risk that I can't mathematically represent, and therefore 100 or 200 psi seems to be about as effective as taking Tylenol to stop the pain of a gunshot wound to the chest. Cave fills, massive steel tanks, cheap (ish) stage bottles, dpvs, etc have made it incredibly easy to take extra gas, so if you see that there's a riskm IMO you shouldn't be throwing 100psi at it to give a false sense of security.
Similar threads
