Do you actually see people diving with pony bottles?

[lermontov]

Then you don’t have any redundancy on the second dive, and you have to have two sets of gear to switch between double and singles. Two reg setups, two BCs, two weight configurations. Using the 80 first gives redundancy for both dives and you use the same gear.

assuming hes wants/needs redundancy ? is he penetrating? why does he need 2 BC hes slinging the AL80?
why not do as max suggested dive the twins and then use the AL80 as a top up with a whip at SI if hes running independat twins he can run one tank down fill it up with whip, admittedly he wont get a full top up but may be a compromise depending on divers preferences to carrying stage /pony

 

[Gareth J]

I keep seeing statements like this and I keep shaking my head. It is for emergency only if that is the gas plan. It is not for emergency only if the gas plan includes its use.

?

I don't quite understand what your point is.

The gas plan is the primary cylinder(s), with sufficient gas to get you and your buddy back to the surface in the event of a normal OG emergency.

A pony cylinder (3litre i.e. small) cylinder is there as a personal bailout cylinder in the event of catastrophic gas failure. You should know the practical limits of the cylinder. In my mind, the limit for a 3 litre is 30m. Beyond this it is not viable. You are into twinset territory. This fits well with the limitations of a single cylinder, you are unlikely to have clocked sufficient decompression to exhaust the 3 litre in the event you have had to 'bailout'. (To be honest beyond 20m I'm on a twinset any way - in the days I used OC).

Ideally, you should be able to complete all the required decompression independently on the 3 litre in the event you have had to bailout. This is always what I plan on.
At worst, you will get back to the surface having completed most of the decompression. Potentially you will have had to use your buddies AS to complete the last of the stop - if they are still with you. If not, you have a helicopter ride and a lot of O2 to breath.
Remember it is far better being on the surface needing recompression than not being on the surface without any gas!

------------------

When you calculate gas normally, 1/3 reserve of the backgas, 50% on the Stage cylinders (if you are using stages).

Again it depends what you are diving and how you are diving. In the old days of OC diving, I used to try to be self sufficient. I could complete the dive on one of the two stage cylinders if one failed, at a real push i.e just travel, or just deco. If you couldn't do this then it was a KYAGB dive (Kiss Your Ass Good Bye). You where reliant on the rest of the team for deco gas, or staged cylinders (on the trapeze), or gas from the surface.
To be frank, I have spent so long diving self sufficient with redundancy, that I am never entirely comfortable being reliant on other members of the team for gas to get me back to the surface in the event of a catastrophic failure.
I find OC diving relaxing if a bit quaint. I like the luxury of infinite gas that CCR gives me. The only negative is carrying a minimum of one ali80. But to be honest, I have been diving with stages I hardly know they are there these days - two stages don't even get in the way of the camera .

PS - Exactly what MAXBOTTOMTIME said.

 

[agilis]

Introducing the tables as part of basic scuba training takes very little time and is a valuable expansion of a new diver's general understanding. It seems to me informed is better than ignorant. In the same way that familiarity with the operating mechanics of the first and second stage of a regulator contribute to a deeper understanding of what is happening and what a diver is experiencing, an introduction to the tables is more important than fish recognition, and enhances a new diver's appreciation of and insight into what a diving computer does.

 

[Gareth J]

I

{using 50% in ponies}

So you planned on using it, yet didn't include it in your plan. Do you not see anything wrong with that?

You didn't read what I wrote, or I wasn't clear.

When using twinsets, (which are our redundant gas supplies,) we used to also take a Pony. The Pony (3litre) would contain 50% Nitrox.
This was used as a flushing gas on the decompression stop (i.e during ascent once shallower than 18m).
The 3 litre was not part of the gas calculation. Because it may be empty, it may fail, you may have a free flow. It was ONLY as an additional safety during the decompression to flush out Nitrogen.
Gas calculation where only done on the back gas rule of thirds, (based on the worst breathing rate in the buddy pair).

Basically, an unusual system , the 3 litre is not part of the dive plan. Its not used to accelerate the stop, to all intense and purposes it does not exist.
The dive is on air, the decompression is calculated as if it is on air (early computers couldn't do in water gas switches anyway).
It had one major benefit, it significantly reduced sub clinical DCI.

 

[teknitroxdiver]

assuming hes wants/needs redundancy ? is he penetrating? why does he need 2 BC hes slinging the AL80?

You can’t just leave the doubles behind and still sling the 80. Doesn’t work that way. If you mean diving both doubles and 80 on the second dive, then that’s the same as was suggested originally, just in the opposite order.

why not do as max suggested dive the twins and then use the AL80 as a top up with a whip at SI if hes running independat twins he can run one tank down fill it up with whip, admittedly he wont get a full top up but may be a compromise depending on divers preferences to carrying stage /pony

Have you done the math on that? You won’t get much at all out of the 80. If you use it as a stage you can breathe it completely empty if you wanted to.

 

[lermontov]

You can’t just leave the doubles behind and still sling the 80. Doesn’t work that way. If you mean diving both doubles and 80 on the second dive, then that’s the same as was suggested originally, just in the opposite order.



Have you done the math on that? You won’t get much at all out of the 80. If you use it as a stage you can breathe it completely empty if you wanted to.

what do you mean by 2 BCs then? I read max post as use the twins first dive and carry Al80 as pony for second (with the twins) maybe max meant just use the Al80 as a single in which case I agree with you

agreed your not getting a full mix but if carrying a pony is uncomfortable for him then its an option -personally Id go fro sidemount and just change tanks or get a second set of twins -it depends on number of factors

 

[teknitroxdiver]

what do you mean by 2 BCs then? I read max post as use the twins first dive and carry Al80 as pony for second (with the twins) maybe max meant just use the Al80 as a single in which case I agree with you

That’s the way I understood him, thus the need for both double and single tank equipment for his proposed solution.

 

[MaxBottomtime]

That's what I meant. Take a second wing for the 80 and either change a couple of hoses to make a single reg or take a second reg. I guess you could also rig the 80 for monkey diving for the second dive.
If you don't have room on the boat just breathe from the 80 during the second dive. I prefer to not sling anything larger than a 40 but I've seen divers with multiple staged 80s. Whatever you're comfortable with.

 

[mainedvr]

You can’t just leave the doubles behind and still sling the 80. Doesn’t work that way. If you mean diving both doubles and 80 on the second dive, then that’s the same as was suggested originally, just in the opposite order.



Have you done the math on that? You won’t get much at all out of the 80. If you use it as a stage you can breathe it completely empty if you wanted to.

Yes that was my original idea, and lots of great input some kind of off what I was asking but good topic still. We have a local dive boat that does a few deeper dives as I said in the 80-100 range and will let you bring doubles but not two sets and they do not fill tanks. So I was thinking of just taking an AL80 slung, breath it down some or to whatever I plan switch over to my doubles, and do my NDL time, taking into account having gas for a second dive. Then on the second dive just use my doubles or breath the 80 down half and take it as extra redundancy or breath it down to nearly empty and leave it on the boat for the second dive. Either way not really asking for permission or anything just more curious if anyone has done this, part of the original post was how other divers on boats or at dive sites look at you when diving a "pony" or whatever lingo you want to use to describe it, when not doing a "tech level" dive.

 

[lermontov]

Yes that was my original idea, and lots of great input some kind of off what I was asking but good topic still. We have a local dive boat that does a few deeper dives as I said in the 80-100 range and will let you bring doubles but not two sets and they do not fill tanks. So I was thinking of just taking an AL80 slung, breath it down some or to whatever I plan switch over to my doubles, and do my NDL time, taking into account having gas for a second dive. Then on the second dive just use my doubles or breath the 80 down half and take it as extra redundancy or breath it down to nearly empty and leave it on the boat for the second dive. Either way not really asking for permission or anything just more curious if anyone has done this, part of the original post was how other divers on boats or at dive sites look at you when diving a "pony" or whatever lingo you want to use to describe it, when not doing a "tech level" dive.

either way is ok id just breath the pony down on one dive and leave it behind on the other if youve got independent twins you still have redundancy if you want to dive with overhead otherwise take half and half