Gas Management for Peacock III/Syphon?

Just curious what kind of gas management plan people use when diving Peacock III, or any syphon for that matter. I've only dove Peacock III once before, and having never been there before, we dove 1/6's. At the end of the dive, that seemed way too conservative. Do people dive it the same as Peacock I? (since both seem essentially no flow). I completely understand the argument that 1/3's is not conservative enough in a cave like Peacock, but what are people really doing in Peacock III? Thanks for your thoughts!

2x gas to exit in reserve

I haven't been in P3 since 2004, but in all the times I've been there, there's never been enough flow to even realize it's a siphon.

Usually I can't tell it is a syphon, so I just add 200 to 300 PSI on top of my usual reserve. There have been a couple of times when the pull was stronger. On those occasions I have been known to dive quarters instead of thirds. For a strong syphon I will dive sixths or look for a different cave.

Mark Vlahos


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Usually 1/4s, never more than 1000 psi penetration. When I see all the duck week being sucked toward the entrance then it's more conservative. Although P3 doesn't usually have much flow I have seen it siphoning at a pretty decent rate a time or 2.

This topic brings back a memory of that system that was a learning experience. About 10 years ago I was diving P3 using alum 80 as travel gas, and 104's as back gas with trimix. Also put a 45 with O2 at the entrance. The travel gas was dropped off after breathing it down 1/3 and continued on to Henley and the rest of the cave on back gas. On the way out switched from the back gas (trimix was even expensive back then) to the travel gas alum 80. On the way out swimming against the strong flow I sucked the alum 80 dry. Still had plenty of gas in the 104's which I switched back to but I was still surprised at how fast I emptied that bottle, and this was not my first dive there.

If you have a lot of gear on you you will notice that flow on exit

Arbitrary rules like quarters or sixths don't make much sense to me. I think you should put more thought into it than that when diving siphons.

I usually dive it in fifths. I look at it this way;

3600 fill
3500 rounded down
700 to get in with
2900 in reserve
1450 for me
1450 for my buddy

That gives each of us twice the gas getting out as we had coming in. If it is syphoning harder, then I adjust fire from there. If I take a stage, then I breath it to thirds unless my buddy is at thirds first, then I drop it when they do.

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Originally Posted by litehedded

if you have a lot of gear on you you will notice that flow on exit

arbitrary rules like quarters or sixths don't make much sense to me. I think you should put more thought into it than that when diving siphons.

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ditto, ditto, ditto

Same here.

We rarely dive to thirds unless we're doing a swimming dive someplace with strong flow out like Ginnie or JB. In no flow/low flow caves we normally pad our gas reserve by reducing the penetration gas by 100-200 psi. In a siphon, we add reserve on top of that based on how much of a siphon we're dealing with, and if it's stronger than anticipated I'll change the plan to increase the conservatism even more. I look at cave diving like I do aviation, where it (almost) never bothers me to stay fat on gas.

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Originally Posted by LiteHedded

If you have a lot of gear on you you will notice that flow on exit

Arbitrary rules like quarters or sixths don't make much sense to me. I think you should put more thought into it than that when diving siphons.

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Not a single person has posted that they use an arbitrary rule like quarters or sixths. Some of us have posted that we sometimes dive 1/4s but everyone so far has posted a few variations. Rather than trying to blame people for something that hasn't even been stated why not contribute something to the thread? For instance, what kind of thought do you put into it when diving siphons?

There are people out there who DO pick a fraction and roll with it. I don't see where anyone accused a particular person of doing that....

You can swim half the freaking cave on a single stage + 1/6ths. Trying to be precise when it's so easy to be conservative is like bringing a graphing calculator to 2nd grade math class. I always attempt to avoid siphon diving if I can go upstream instead (such as a circuit), but if I can't, I'll look in my log book for a similar flow cave, see how far I got on 1/3rds when going against the flow and know that's the furthest I can be when I hit 2/3 remaining.

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Originally Posted by RN

Not a single person has posted that they use an arbitrary rule like quarters or sixths. Some of us have posted that we sometimes dive 1/4s but everyone so far has posted a few variations. Rather than trying to blame people for something that hasn't even been stated why not contribute something to the thread? For instance, what kind of thought do you put into it when diving siphons?

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I didn't really see any thought explained in your post either, just two completely random numbers with no explanation.

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Originally Posted by PfcAJ

I don't see where anyone accused a particular person of doing that....

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The implication was there.

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Originally Posted by jj1987

I didn't really see any thought explained in your post either, just two completely random numbers with no explanation.

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But Brian didn't provide anything at all other than criticism. I provided a starting point and responded directly to the OP regarding what I do at P3. The OP simply asked what people are doing. Brian decided to come in and criticize everyone's response stating

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Arbitrary rules like quarters or sixths don't make much sense to me. I think you should put more thought into it than that when diving siphons.

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Since he brought it up I'd like to read what kind of thought he puts into it.

Somebody call a whambulance! I think you're just really reading into things and jumping to a false conclusion. Guilty conscience? Or just mad because you gave an arbitrary fraction?

Last week there was no noticeable flow at P3. Dove backmount 104's. dropped off a deco bottle at the ledge and didn't notice anything different after picking it up on the way out.

However it has rained a good amount since a week ago. Not sure how that affects things in the area...?

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Originally Posted by PfcAJ

Somebody call a whambulance! I think you're just really reading into things and jumping to a false conclusion. Guilty conscience? Or just mad because you gave an arbitrary fraction?

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Now you're just getting personal. But that doesn't surprise me from you.

There were responses to the OP. If you re-read the OP it asks "what are people really doing in P3". You responded with 2x the gas to exit, which is 1/4s. Mark and I answered with a couple of variations. My response was due to the fact that the amount of flow siphoning in will vary, as you can see by my comment about the duck weed. So actually looking at this again, it appears Brian may have been directing his comment at you seeing as you are the only one that gave an arbitrary rule...

As for a guilty conscience, not the case. Just because I didn't thoroughly explain my technique for gas calculations here doesn't mean I don't do something more than an arbitrary number. I use something similar to what I do for DPV diving, which I'm sure would probably blow your mind. And I don't see any arbitrary fraction in any of my posts.

But hey, again, I don't expect much more from you anyway since you are the one who posted an arbitrary fraction...

Thats not what I said, Rob.

1/4s would be what I said if we were talking about a no flow cave. A siphon has flow. That's why its called a siphon. Therefor, I didn't say 1/4s. 2x the gas to exit is different than 1/4s in a siphon.

I would expect just about anything you cook up to blow my mind.

Maybe we can get the NFSA (not the National Flying Squirrel Association) to install a flow meter at P3.

this thread got fun.
the butthurt is strong in here

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Originally Posted by LiteHedded

this thread got fun.
the butthurt is strong in here

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Two buddies of mine were in P III yesterday and said the flow was virtually non existant at this point in time. Since my default buddy is a living flow-detector, I would tend to believe him and any of the suggested (conservative) gas plans would most likely be fine.

The flow between P2 and P3 is almost nil as well, and if there is flow in the system, it's usually felt there more than anywhere else. IMHO the flow in the restriction there makes a much easier to gauge indicator of the flow in P3 over all.

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Originally Posted by LiteHedded

...Arbitrary rules like quarters or sixths don't make much sense to me. I think you should put more thought into it than that when diving siphons.

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Not that I has direct impact on the conditions at present, but I have a very distinct memory of completing a dive at P3 during high water.

After exiting we broke the gear down then went back to look at the entrance. during that time, the river had come up enough to where it was now pouring dark brown water into the basin which was in turn draining into P3.

Had we exited 20 or 30 minutes later, it was likely we would have experienced a "character building" exit.

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Originally Posted by diveconjeff

Not that I has direct impact on the conditions at present, but I have a very distinct memory of completing a dive at P3 during high water.

After exiting we broke the gear down then went back to look at the entrance. during that time, the river had come up enough to where it was now pouring dark brown water into the basin which was in turn draining into P3.

Had we exited 20 or 30 minutes later, it was likely we would have experienced a "character building" exit.

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Yea that happens there sometimes