Best type of Pony Tank setup?

[Big-t-2538]

anything you carry can introduce an entanglement problem. As long as you are streamlined in your configuration, you reduce this risk.

Stop right there...

You see..."anything you carry can introduce an entanglement problem"

To me it doesn't matter how streamlined a pony is....it is an extra piece that I certainly don't need b/c I dive with a buddy. There are many advantages of diving with a buddy as your "pony". 1 - You know you're going to get a working reg in the event you go OOA (you're buddy is breathing off of it right now) 2 - You know that there's enough gas conserved in his tank to get both of you back to the surface b/c you planned ahead for the "worst case scenario". 3 - you're buddy can give you gas in the event you can't move to get to your pony. 4 - you're buddy can un-entangle you in the event you're all tied up

When diving with good team communication, how does a pony help at all? IMO it is an extra piece of equipment that (no matter how streamlined) adds risk & task loading to a dive that isn't necessary. Specifically, entaglement, added weight that has to be compensated for, constant monitoring of the SPG, and it increases drag. Are just a few things off the top of my head.

That aside, I can see the use for a pony if and only if you're solo diving...I'm not a proponent of solo diving...thus I don't like ponys.

 

[Big-t-2538]

I wasn’t being sarcastic. When I asked I did not realize that you where diving single tank and simply wanted to know what you did with the hose.

I know...I just wanted a good reason to use a "simple life" reference today...I didn't intend to upset anyone...sorry if it came across that way.

 

[Genesis]

Stop right there...

You see..."anything you carry can introduce an entanglement problem"

To me it doesn't matter how streamlined a pony is....it is an extra piece that I certainly don't need b/c I dive with a buddy.

Stop right there

I hope you've run those "rock bottom" numbers conservatively. When I do so, for a single AL80, I find that for a deep dive (say, to 100') I am roughly operating on thirds. That makes the entire thing a "touch" dive because I need the rest for redundancy so my buddy has gas if he needs it.

Now if you're diving doubles this does not apply, because you can protect half your gas even with a failure, AND you have more to start with.

But, you can solve the same problem by slinging a pony bottle......

 

[NEWreckDiver]

Stop right there...

You see..."anything you carry can introduce an entanglement problem"

To me it doesn't matter how streamlined a pony is....it is an extra piece that I certainly don't need b/c I dive with a buddy. There are many advantages of diving with a buddy as your "pony". 1 - You know you're going to get a working reg in the event you go OOA (you're buddy is breathing off of it right now) 2 - You know that there's enough gas conserved in his tank to get both of you back to the surface b/c you planned ahead for the "worst case scenario". 3 - you're buddy can give you gas in the event you can't move to get to your pony. 4 - you're buddy can un-entangle you in the event you're all tied up

When diving with good team communication, how does a pony help at all? IMO it is an extra piece of equipment that (no matter how streamlined) adds risk & task loading to a dive that isn't necessary. Specifically, entaglement, added weight that has to be compensated for, constant monitoring of the SPG, and it increases drag. Are just a few things off the top of my head.

That aside, I can see the use for a pony if and only if you're solo diving...I'm not a proponent of solo diving...thus I don't like ponys.

We are definitely talking about different types of diving here. I subscribe to theory that you need to dive to be completely self-sufficient. Being able to rescue yourself and without any assistance from anyone.

Does this mean that I dive sole, not really. But they are not glued to my hip either.

There is more than one way to skin a cat.

 

[Big-t-2538]

I hope you've run those "rock bottom" numbers conservatively. When I do so, for a single AL80, I find that for a deep dive (say, to 100') I am roughly operating on thirds

O.K....let's say 100'....what is the minimum pressure I have to retain to get both me and my buddy to the surface assuming a total gas loss by 1 diver?

Assumptions : Each diver "panics" and has a SAC for the whole ascent of 1cu.ft. per minute, we're diving an AL80 tank, the planned ascent is 30fpm between stops, 1 minute stops at each 1/2 max depth, 30, 20, & 10 feet.

O.K...buddy has signalled OOA....I assume we take 1 minute to solve the issue and get started on our ascent.

We have a total ascent time of 8 minutes if we assume the stops are 30 second stops with 30 second moves.....at an average depth of approximately 50' (100+85+60+50+40+30+20+10 / 8) = 50 feet or 2.51 ATA.

so we have a total of an 8 minutes ascent...1 cu.ft. per minute for 2 divers, so that's 16 cu feet of gas needed * 2.51 ATA = 40 cu ft.

40 (cu ft.) / 77 (cu ft. of actual volume in an AL80 tank) = 0.52 * 3000 psi = approximately 1550 psi.

So...my buddy and I leave the bottom of a 100' dive when either of us hits 1550 psi.

This plan that we dove in the straits this summer gave us about 12 to 15 minutes on the 100' wreck that we dove.

 

[Big-t-2538]

I agree with the idea of being able to rescue yourself....but times arise when that won't be the case, so I don't see the need to plan for it....you have a perfectly capable buddy.

Yes, clearly we have a difference of opinion....there is nothing wrong with that.

We are definitely talking about different types of diving here. I subscribe to theory that you need to dive to be completely self-sufficient. Being able to rescue yourself and without any assistance from anyone.

 

[MikeS]

Oso we have a total of an 8 minutes ascent...1 cu.ft. per minute for 2 divers, so that's 16 cu feet of gas needed * 2.51 ATA = 40 cu ft.

40 (cu ft.) / 77 (cu ft. of actual volume in an AL80 tank) = 0.52 * 3000 psi = approximately 1550 psi.

So...my buddy and I leave the bottom of a 100' dive when either of us hits 1550 psi.

I based the calculations on the following:
* One minute at depth to start ascent.
* 30 ft/min ascent rate to safety stop at 15 ft.
* 3 min safety stop at 15 ft.
* SAC rate of 2.0 cu. ft./min (1 for me and 1 for my buddy) we’re not swimming were going up.
* 77.4 cu. ft. in an AL 80 at 3000 psi or 38.8 psi per cubic foot.

So it comes out like this:
100 ft. 1075 psi
90 ft 951 psi
80 ft 835 psi
70 ft 627 psi
60 ft 535 psi

So basically you need 10 psi per foot of depth plus whatever safety margin you feel comfortable with, let’s say 200 psi for this exercise. On a multilevel dive where you start deep and work your way up, you need to start up at 10 times your depth plus 200 psi. Keeping in mind that this is the point where you head straight to the surface, not start looking for the anchor line. If you want to be more conservative add a bigger margin.

I prefer to dive with PS HP 120 and the numbers are even easier to remember, 10 psi per foot which includes an almost 200 psi margin.

Mike

 

[Genesis]

Sigh....

Ok, let's run some numbers here.

We will assume an RMV of 0.7cf/min, which is fairly close to "normal" for most folks with some experience. There are those of us who do significantly better (I do much of the time) but you can't PLAN on that.

We will also assume you are at 100', with a buddy, and one of your regs locks up hard (no gas) OR you blow an LP hose (equally bad). Whatever the case, you now have ONE tank between the two of you.

Ok, my usual stop profile from a 100' dive is:

1 minute @ 70'.
1 @ 50, 40 and 30.
3 @ 20.
~2-3 from 20 to surface (actually usually 1ft/10 seconds, which is roughly 3 minutes, but surge sometimes makes the last 3-4' effectively a non-issue.)

We'll call the AVERAGE depth on ascent 33' or 2 ATA just to make the math easy; that's a bit conservative but that is ok.

Alright. We start at 99', or 4 ATA. We have two guys now on one tank, who are breathing 5.6cf/min. We give them 1 minute to figure out that this is an "abort" situation and not fixable.

We now bring them to the surface on our ORIGINAL ascent plan, and we figure they might be a bit "fast" getting to the 70' stop. Remember, the idea here is not to blow stops, but people WILL be a bit excited! So we do 2.8cf/min (average) for 10 minutes, or another 28cf, for a total of 33.6cf of gas.

But wait. We made a bad assumption here. We assumed that nobody's breathing rate would be jacked by the problem. Yeah, right. Conservatively, the guy with the problem will have his RMV increased by 50%; let's factor that in. So now we have 3.5cf/min for 10 minutes, + 7.0cf for the first minute, or 42cf.

Now this is a bare minimum, as it does not allow for any increase in the donor's RMV, which is of course also likely.

But this puts "rock bottom" awfully close to THIRDS for a single AL80!

With a HP100 or HP120 things get substantially better, but for the average guy with an AL80 @ 100', you've got a real problem if someone TRULY needs to bail and you're using the typical "be back at the line @ 1000 psi" type of dive planning. You WILL run out on the way up.

A 19cf pony will ALMOST supply one of the two divers in this scenario. If you had one, you could give it to the OOA diver and ascend with him. He would probably run out at the 20' stop. When he does, NOW you give him your long hose, and you have plenty of gas.

 

[Uncle Pug]

UP, back gas is a single for rec diving and is out of service due to neck oring rupture. That leaves your buddies long hose or the 30cft pony being handed to you. If you descide to take the long hose, why would you take it instead of the pony?

I would use my back gas rather than just let it fizzle away... a blown neck o-ring doesn't put the tank out of service... it just ruins your SAC for the dive.

IF the SPG got too low I would take the second stage (on a long hose... yes we dive the same configuration whether singles or doubles) my DIR buddy would have extended at the ready. Since we have practiced airsharing ascents using the long hose as well as making safety stops, this would be the easiest.

 

[Uncle Pug]

How do you stow the extra hose?

as has been described... not stuffed but down the right side under the light can then across the chest and around the back of the neck and into my mouth from the right.

A misconception that folks have (not necessarily you) is that the hose is wrapped around the neck... it is only across the back of the neck. This is the most streamlined and snagless configuration possible. It is very easy as well as quick to hand off the second stage by dipping the head slightly. True... it doesn't work with snorkles.

I personally find the long hose makes doing air sharing ascents much easier as each diver controls their ascent independent of the other and can separate enough to even complete tasks such as shooting a bag without undue concern about entanglement. We practice this. It is fun.