PONY Question

[Northeastwrecks]

MikeS once bubbled...
So to answer a derivative of Northeastwrecks’s question, what good is a 30 cu. ft. pony, my answer is that provides sufficient gas to float a surface marker from 120 feet and make a safe ascent, including safety stop.

To all of you that insist we should all be diving doubles, thank you for your advice. We are appropriately envious. But after careful consideration many of us have determined that doubles, and h-valves, are not a practical solutions. I submit that your efforts would be better spent helping us to understand the limitations of ponies rather than continuing to blast them because at least in my case I can learn from the former and will continue to ignore the later.

Mike

I agree that a 30 is not inappropriate. I use the 46 because it's primary purpose is for deco. That fact that it a form of redundant backup is a bonus.

I'm not suggesting that everyone dive doubles. I'm still waiting to get mine, primarily because of the expense.

Pony's have their place, so long as you plan appropriately. You have done the calculations and tested them. You know the limits and that is important.

My point is that a small pony does not provide the proper backup.

 

[Scuba446]

My PONY selection is based on diving no deeprer than 60 ft - right now, and is there not for ADDED BT or gas, but ONLY IF my K-Valve was to fail.

All my buddies and I are FIRM believers in checking our PSI gauges habitually - and OFTEN! So the pony isn't there so I can rely on it for added BT or deco stops. Its there ONLY in case of a K-valve failure or 1st stage failure on my AL80 - and thats it.

If I was seeking longer BT's, etc. - it'd be doubles. As I said before, as a newbie and FT college student - a $2k twins rig isn't do-able.

 

[jonnythan]

Scuba446 once bubbled...
My PONY selection is based on diving no deeprer than 60 ft - right now, and is there not for ADDED BT or gas, but ONLY IF my K-Valve was to fail.

All my buddies and I are FIRM believers in checking our PSI gauges habitually - and OFTEN! So the pony isn't there so I can rely on it for added BT or deco stops. Its there ONLY in case of a K-valve failure or 1st stage failure on my AL80 - and thats it.

So how much gas will you need to ascend from 60 feet with a stressed SAC for when your valve O-ring blows?

 

[Northeastwrecks]

jonnythan once bubbled...


The way I calculate it, that's an SAC of about 1.2 cf/min to make it to the surface. It's closer to 1.7 if you ran out of air a minute into the 20' safety stop.

I've barely got 40 dives, and my SAC recently has worked out to be about 0.6 - 0.7 cf/min, and I'm in the middle of the pack for my diving group.

What was the pony's starting pressure?

I don't remember the starting pressure, but I do remember checking to see that it was fully pressurized.

My SAC rate varies between 0.4 and 0.7, depending on whether I'm working, working hard or hanging.

I reviewed my log for that dive. I started on the pony about 1 minute before we returned to the line. I deployed the pony at about 95fsw. I signaled my buddy, unhooked the line and fouled the hook (2 minutes max). I did this because we were the last divers up and this was our second dive of the day. Sending someone down on short tanks and without a proper SI would have been dangerous and there was no way the boat was leaving unless the Captain cut the line. (I'd tied off to the hull of the wreck). Besides, it was my responsibility and, unless the emergency were life threatening, I would do it in real life.

Our ascent rate was about 20 fpm, with occassional increases to 30 fpm.

I did not suck the bottle dry, but was getting too close for comfort.

BTW, my calculations show that a SAC rate of 0.6 would come close to emptying the bottle. My numbers are rough, but they match what I experienced and what my decoplanner claims will happen.

My point is that you don't want to push your calculations too close to the edge. Assume that your SAC rate will be up. Assume that you might not be able to leave the bottom immediately. Assume that you buddy might also need air. In that case, what is wrong with a properly sized bottle.

 

[MikeS]

Scuba446 once bubbled...
My PONY selection is based on diving no deeprer than 60 ft - right now, and is there not for ADDED BT or gas, but ONLY IF my K-Valve was to fail.

You can easily test it. On your last dive of the day switch over to the pony before making your ascent. Spend a minute or two at depth. In a real situation you will have to asses the situation and adjust. In the example you gave of a failed K-valve, the escaping air will make you more buoyant and you would have to adjust to regain neutral buoyancy. Don't forget that the increased task loading will make buoyancy control more difficult and that if in that situation your power inflator will no longer work to add air. See how much air you end up with.

Make sure that your buddy knows what your doing before hand so they can keep an eye on you.

Mike

 

[Scuba446]

OK..

 

[Dryglove]

I think everybody is missing the point here.If you were doing a rec dive at 60 ft and your air supply somehow got cut off,would you rather do a emergency ascent(blow and go) or have a 19cuft pony and skip your safety stops(i would take the pony,thats just me though).If you can fit in your safety stop,then more power to you.I also dive with a pony for now....it is for emergency use only and i know my limitations with it.It would be wise to carry a back up with enough gas for all safety stops.Doubles would be awesome but sometimes we cant have our cake and eat it too(yes its a money thing and what about all your buddies diving singles).
I have recently discovered dir diving and am acquiring gear to take dirf in a few months.Why am i doing this.I think the whole system makes sense.I dont agree with some of the attitudes but the majority of guys that are dir on this board have been friendly and very helpful.They have an extremely safety minded approach towards diving,gear and buddy awareness.Im just gonna leave it that so i dont get bashed by the dir haters....lol.

DSAO

 

[Northeastwrecks]

lal7176 once bubbled...
I think everybody is missing the point here.If you were doing a rec dive at 60 ft and your air supply somehow got cut off,would you rather do a emergency ascent(blow and go) or have a 19cuft pony and skip your safety stops....
DSAO

Option D. None of the above.

I would rather have my 46 cu. ft. deco bottle filled with EAN50 and a buddy with a fully working system and a 7 ft. hose (whether on doubles or singles). At 60 ft., my deco mix will act as a nice, O2 rich redundant gas (I normally deploy it at 70). I can do whatever I need to in order to control the situation and make sure that other people are not in danger. Then I can make a leisurely ascent with proper stops.

What people are forgetting is that 19 cu. ft. is not the only size pony out there. Aluminum is the preferred construction for deco's and stages, so even larger sizes are not particularly expensive, especially since you already have a pony regulator. Moreover, if you pick the right gear, you can still use it when you progress to more technical diving (assuming that is an ambition).

Figure the absolute worst case you can imagine. For example, assume (1) catastrophic back gas failure; (2) a fair distance from the ascent line; (3) with a buddy who is also low on gas, or injured, or entangled (you pick).

At 60 fsw, and regardless of your SAC rate, a 19 cu. ft. bottle will not allow you to deal with the situation. A larger bottle, on the other hand, might. You could (1) assist buddy; (2) shoot a lift bag; and (3) conduct an ascent, buddy breathing if necessary and appropriate. You might not make it all the way up, but you will be in better shape.

Personally, I would rather carry the larger bottle. I don't want to be put in a situation where I have no options. More gas = More options.

The situation described above is unlikely. So is the equipment failure we've been discussing. To me, the marginal cost is worth it.

 

[Scuba446]

"Moreover, if you pick the right gear, you can still use it when you progress to more technical diving (assuming that is an ambition)."

Thats not a big goal of mine right now. I'd much rather tote a 19 in cu bottle in 60 ft of fw than an AL40. Kinda overkill, I think for what we are currently doing now.

 

[Northeastwrecks]

That is fine, but that's not the real point of my post. It's sort of a bonus that the equipment has other uses.

How about the increased safety factor?

BTW, I'm not trying to get on your case personally. I understand what you are trying to do. I'm simply suggesting that there are better ways to accomplish it.