Used the 13 cu-ft pony this weekend

[In10se]

Ok..i understand..but a 13 or a 19 is PLENTY to get out of trouble?

Well, by PLENTY I'm not trying to imply there'd be enough time to order in a pizza but considering it's a redundant air supply ... meaning the buddy would be there during ascent ... PLENTY means enough to get topside safely.

You did ask a very good question.

I'm new, but as far as I've learned a pony is nothing but a redundancy. I gotta say that so far I like the streamlined method of combining the secondary with the power inflator on the BC. One less combination of things to worry about failing. If either one of us goes into an OOA situation the OOA buddy gets the primary and the the secondary gets some use. With proper gear maintenance, and a proper dive plan in place, a pony is just hanging there in case Murphy shows up. If Murphy kills my secondary then the pony will get used.

Yeah yeah yeah ... I know ... that was all nos417 basic dive 101 stuff. I just put that out there for reference.

lets assume that Murphy's due diligence causes my GTS plan to become a reality. If we're both (both meaning my wife and I) running 19cft pony tanks, can we get from 75'/100' back to topside? Is a 19cft going to qualify as PLENTY?

I'll test the theory of PLENTY sometime in the next month and post how much emergency use I get from a 19cft, with my poor sac rate, on an ascent. I'll even wind myself a little to stimulate a stressed situation, and I'll include an extra deco stop for good measure. I'll also keep a log on all this so that if the 19cft pony runs dry we'll know what would have been needed to get the job done. I'll make sure to have a freshly filled main tank, I'll do this on my first dive so I'm also fresh, and I won't do this without a well seasoned DIMWIT along for a buddy. My fellow DIMWIT can add cometary on the experience.

With a test run on a 19cft pony I'll better be able to answer the question: PLENTY? Dam good question, and I don't think I wanna find out the hard way.

 

[merxlin]

Once you start diving as a team instead of everyone for himself, the latter of which is unfortuneately very common in recreational diving, you'll find that the deeper recreational dives, i.e. say 90 ft+, require more gas than 13 or 19 ft^3 to get you AND your buddy to the surface in a safe/slow/controlled manner. I am not considering solo diving here, that would be a whole separate thread. I'm sure you can do some calculations yourself?

OK, so at 90 ft with a very stressed sac rate of 2.0 would be a consumption rate of 16 cu/ft minute at 90 ft. and at an accelerated ascent rate of 1 ft/sec you could get one person to 60 ft in 30 seconds, or 8 cu.ft of air. Your rate is now 8cf/min so need 4 cu ft to get to 30 ft. Rate is now 4cf/min and you have 7 cf of air (19-8-4). 15 seconds to 15 ft uses 1 cf, and now your rate is 3cf/min, so you could do a 2 minute stop at 15 ft and make the surface.

Is this optimal? No. Does it keep your buddy alive and not bent? Probably. And as has already been pointed out, if you AND your buddy are OOA at 90 ft either you have the worlds worst Karma, or you effed up real bad. Then it might still be possible to get there if you both keep calm. So for the recreational diver, a 19 should be enough in most situations.

 

[sheck33]

OK, so at 90 ft with a very stressed sac rate of 2.0 would be a consumption rate of 16 cu/ft minute at 90 ft. and at an accelerated ascent rate of 1 ft/sec you could get one person to 60 ft in 30 seconds, or 8 cu.ft of air. Your rate is now 8cf/min so need 4 cu ft to get to 30 ft. Rate is now 4cf/min and you have 7 cf of air (19-8-4). 15 seconds to 15 ft uses 1 cf, and now your rate is 3cf/min, so you could do a 2 minute stop at 15 ft and make the surface.

Is this optimal? No. Does it keep your buddy alive and not bent? Probably. And as has already been pointed out, if you AND your buddy are OOA at 90 ft either you have the worlds worst Karma, or you effed up real bad. Then it might still be possible to get there if you both keep calm. So for the recreational diver, a 19 should be enough in most situations.

If you just care about getting to the surface and you don't care in what shape you get there then yes sure by all means.

My example was meant to illustrate that it take more than 13 or 19 ft^3 to do a proper* ascent from 90 - 100ft. After 15 - 20 min at around 100 ft, which is a pretty typical recreational dive, rocketing to the surface will have consequences.

* of course we can debate about what a 'proper' ascent looks like...

Lets take your example here. SAC of 2.0, which is pretty high but not unthinkable, at 90ft means 2 ft^3/min x 3.72 ATA = 7.5 cuft/min for on person. When a problem develops it takes time to recognize it and decide on action, you will likely spend at least 1 min or more doing that. Just recognizing there is a problem takes 7.5/13=58% or 7.5/19=40% of your available air supply depending on which tank you take. Not very comforting numbers.

For example using the same reasoning leads to the conclusion that an Al80 is not enough to do 100ft dives.

 

[wedivebc]

Once you start diving as a team instead of everyone for himself, the latter of which is unfortuneately very common in recreational diving, you'll find that the deeper recreational dives, i.e. say 90 ft+, require more gas than 13 or 19 ft^3 to get you AND your buddy to the surface in a safe/slow/controlled manner. I am not considering solo diving here, that would be a whole separate thread. I'm sure you can do some calculations yourself?

Since team diving negates the need for a redundant breathing system in recreational diving your argument is pointless. The pony negates the need for a team member to supply or recieve gas.
You are saying the 13cuft is inadequate when in reality it is only inadequate for the type of diving YOU chose to do, but is quite adequate for the use the OP intended.

 

[SparticleBrane]

I'm still wondering how the OP thinks he was successfully diving in a 3-knot current.

 

[fl-diver]

I'm still wondering how the OP thinks he was successfully diving in a 3-knot current.

I don't know what you consider "successful" but we dive in 3 knot current pretty regularly in south Florida (the Palm Beach/Jupiter area). Fortunately the current generally runs parallel to the reef ledges.

I see this discussion all the time. Obviously it is not always practical to dive doubles and this guy wasn't even scuba diving initially. He took a pony bottle down to collect some gear and fish. Luckily he had backup scuba gear on the boat. He didn't die of shallow water blackout, he recovered his gear, didn't get bent and had air left over in his pony bottle. I would call that a success.
I guess he should have done a deep stop and at least a 3 minute safety stop to off gas from his couple minutes on the bottom.

I want to see pictures of the fish.

 

[merxlin]

If you just care about getting to the surface and you don't care in what shape you get there then yes sure by all means.

I was using an OOA situation for recreational divers. 1ft/min was the norm for a long time, yet I noted it as an accelerated rate based on today's standards.

My example was meant to illustrate that it take more than 13 or 19 ft^3 to do a proper* ascent from 90 - 100ft. After 15 - 20 min at around 100 ft, which is a pretty typical recreational dive, rocketing to the surface will have consequences.
* of course we can debate about what a 'proper' ascent looks like...

I believe 20 minutes bottom time would be a stretch for a recreational diver just based on air consumption alone.

Lets take your example here. SAC of 2.0, which is pretty high but not unthinkable, at 90ft means 2 ft^3/min x 3.72 ATA = 7.5 cuft/min for on person. When a problem develops it takes time to recognize it and decide on action, you will likely spend at least 1 min or more doing that. Just recognizing there is a problem takes 7.5/13=58% or 7.5/19=40% of your available air supply depending on which tank you take. Not very comforting numbers.

For other emergencies I agree. But if the dive was planned at all, and BOTH members are not OOA, then a slower ascent is possible with the OOA buddy using the pony for ascent and then possibly having to use the Octo from the donating diver for final safety stops, etc. In an OOA situation, I would not take 1 minute to determine cause of action. Pony up the OOA diver, and slowly head for the surface. That doesn't take a minute.

Again it is not ideal, but is better than not having the extra 13 or 19 ft of air.

 

[spectrum]

Here's an old post that works up a gas requirement. Answering the question without a scenario or limits is just opinion.

In the old post you can see that if nothing goes favorable to worst case then a 19CF won't let you make a SOP return to the surface. Significant problem solving is perhaps the biggest risk since that keeps you at a high usage depth. The safety stop should be expendable but does much less to help the gas budget.

Pete

 

[SparticleBrane]

I don't know what you consider "successful" but we dive in 3 knot current pretty regularly in south Florida (the Palm Beach/Jupiter area). Fortunately the current generally runs parallel to the reef ledges.

How do you KNOW that it is 3 knots? How did you actually measure it?

 

[magicwanz]

How do you KNOW that it is 3 knots? How did you actually measure it?

It's been measured for years, 2 m/s or 4 knots is not uncommon.

Researchers use undersea cables, current meter moorings and Pegasus profilers, and all three methods produce transports that are within 1-2 Sv of each other.

The Florida Current

Also note that the seasonal transport for the Florida Current is typically at its maximum in the month of July.

Regards,

Chris