Pony bottle skills

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MaxBottomtime:
I use an isolation manifold and backup reg in case of reg failure or tank failure. While both are rare, I am prepared for them without having to carry an extra tank and reg that I hope to never use. To me, diving with a pony is like keeping a spare gas can in the back seat of your car. Sure, it's there if you need it, but simple trip planning and watching your gauge/knowing your car's milage works very well.
I disagree on two points, if I am driving on normal roads there is a gas station every few miles, if one is off road spare gas could make the difference between a long walk and driving. So far in 30 years of diving I have yet to find a refill handy while low on air.
Secondly many boats her in NJ require a pony, i doubt the captain will change his policy from what is said on this board. Everybody makes valid points from where they stand on this issue. Dive what makes you feel safe, and be the good buddy that everyone is refering to.
 
OE2X:
You want to be neutral at the end of your dive when you tank goes much more positive. Generally this means about a 10 pound swing.

AL80s are only a 5 lbs swing.

I could believe that being negative enough to get down at the beginning of the dive, could lead to roughly neutral at the end of the dive if you had +5 lbs from the air, minus a couple lbs for wetsuit compression at 15 fsw and maybe start a lbs or two negative to get down.

This probably works for this guy, but fails miserably with drysuits and big tanks.
 
lamont:
AL80s are only a 5 lbs swing.
.

Ooops you are right. Been quite a while since I dove AL80's.

Still a 5 lb swing is a fair bit to deal with. I can generally handle the 2.5 lb swing of an empty 40 as long as I still have back gas.
 
Okay, lets talk buoyancy control, a subject I've written papers about in years past (many years past, by the way--IQ6 & 7). If a person starts out neutral, and by neutral I am saying neutral on a full breath, at the surface at the beginning of a dive, what is that going to do to you at the end. It has a lot to do with what types of tanks you are diving, and how many. I usually dive either my twin steel 42s (1800 psi service pressure--the "old" LP tanks), or a steel 71.2 (64.7 cubic feet at 2250 psi). The buoyance characteristics of my twin steel 45s is approximately 2.4 pounds per cylinder, or 4.8 pounts total (negative, they don't become positive, even in salt water). The published data I got on a single 71.2 cylinder is that they are negative 2 pounds full, and positive 3.5 pounds when empty. These figures are for salt water, and the difference is about the same (4.8 pounds and 5.5 pounds). I was given two AL 80s, and they go from a negative 3.4 pounds to a positive 2.5 pounds), about a six pound difference.

Now, if I am at eye level on a full breath at the beginning of a dive, I will be at eye level at the end of a dive at the surface with a full exhale (I have a 5 liter vital capasity). If I inhale completely (remember Archimedes' Principle), and fill my lungs with 5 liters of air, I have displaced:

5 liters = 0.176573334 cubic feet
Sea water weighs 64 pounds per cubic foot.
0.17657 cubic feet times 64 pounds per cubic foot equals 11.3 pounds
(0.17657 ft3 x 64 lbs/ft3 = 11.3 lbs)

This means that I can more than compensate for the gain in buoyancy of 5 pounds from breathing alone. This is the art of diving, to be neutral at all times during a dive.

A wet suit looses buoyance at depth, and hence we developed buoyance control devices (BCs; I say "we" because I was one of those doing the experimentation and publishing on the subject of buoyancy control in those days). This was done in response to wet suit diving, especially in colder waters. Wet suits loose almost all their buoyance by 33 feet in fresh water (probably a bit deeper in salt water). How do I know? I took off my weight belt in Clear Lake in the 1970s, and tied it to the boat anchor. I was at perfectly neutral buoyancy. When I wanted to surface, I simply went up to my weight belt, and put it back on. Those were the days when I wore 16 pounds of weight in fresh water, and 22 in salt water (it's a bit more now, with 20 pounds more body weight).

Dry suits were a different story. For years none of us used a buoyance control device when diving dry suits. We put on a CO2 life vest in case of a leak, and loss of the suit's buoyancy, but BCs were not used in the early days of dry suit diving.

This is how Sport Diving was conducted early on, and how we taught buoyancy control. I emphasize that this is "Sport Diving," and not "Technical Diving."

Let's look at DIR technical diving, as was posted above:

Web Monkey said:

Anybody can make it to the surface. The trick is to do it without getting DCS.

Can you swim 60 feet in 2 minutes then stop for three minutes and wait while still underwater?...

A couple of steel tanks, an aluminum tank or two, a few regulators, a manifold, a couple of dive lights lights, a backplate, wreck reel, and maybe a camera and a couple of strobes while diving in fresh water would probably do it...

I will answer these questions, but first let's talk about buoyancy of tanks. His "couple of steel tanks" are probably HP120, 3500 psi (overfill) tanks, which are -18.1 pounds each when full, and -9.2 pounds when empty, a swing of 8.9 pounds each, or 17.8 pounds for twins. There is no way of compensating this weight swing with breath control--you must depend on the BC (Cousteau put floats on the triple tanks they used when he was in a similar situation diving deep). Add to this the other tanks, and the "wing" becames a must. Also, because the tanks are now a part of your weighting system for your suit, you no longer have the option of taking them off. Note the huge difference in pressure between full and empty; when you do this, you get greater buoyance changes.

This is why I have stayed with the older cylinders--I like their buoyance characteristics and I don't like the newer cylinder's buoyancy characteristics. I have seen new students with these new cylinders so overweighted in a pool, wearing only the scuba and no wet suit, that performing simple tasks such as staying afloat for an extended time with no air in the BC was nearly impossible for a small woman in the class.

Now, Web Monkey asked how to do an emergency swimming ascent without getting DCS? It is easy--you don't go near the "knife edge" of the no-decompression limits for Sport Diving. Web Monkey is obviously a technical diver, and there are different parameters for technical diving. Talking about DCS, I still have not had an adequate answer to my original question--why don't technical divers insist on a decompression chamber for their decompression dives? If you cannot surface without risking DCS, you are not Sport Diving anymore, and technical divers are at high risk of DCS and dying because they have no chamber available. Can I swim 60 feet in two minutes and complete 3 minutes of a precautionary stop in an emergency swimming ascent? No, I cannot, but I also don't need to either. Technical divers, who either are decompression diving or at the edge of the no-decompression tables, do need to. They probably should also have periodic long-bone x-rays to see whether they have experienced "silent bubbles" and may have asceptic bone necrosis from it (non-symptomatic).

Now, about the original purpose of this thread, using a pony bottle. If you want to Sport Dive, you probably don't need one. If you get into technical diving, you must have one (or one of the several alternatives). It simply depends upon what type of diving you are doing.

One last piece of information. In order for diving instructors to keep their exemption from the Commercial Diving Regulations, they are required to dive with either J-valves or a pony bottle (per the OSHA Commercial Diving regs, Appendix C). These instructors are also required to do no-decompression dive profiles to maintain this exemption. If they do not, then a decompression chamber is required under the Commercial Diving Regulations. The requirement for the pony bottles for diving instructors is probably the reason the charter boats now require them. Only diving instructors who are employees come under these regulations, which is why probably most DIR instructors are independent contractors. If they aren't independent contractors, and teach decompression diving, then they are probably in violation of OSHA regulations. You can check them out at:

http://www.osha.gov/SLTC/commercialdiving/

http://www.osha.gov/SLTC/commercialdiving/standards.html

SeaRat
 
John, I think it is useless. The divers today are "tech" driven even in a recreational circumstance. Rec dive, tech dive bla, bla. You were writing papers on diving before some of these fellows were born.
Pony is a hot botton word, I think I would call my pony if I were to have one an assymetric doubles rig--lol.
Like you I still use the Navy Tables and I think we dive alot alike in method and equipment and style and we both often solo dive.
I saw several posts in this thread claim that without their favorite buddy they would just drink beer and stay dry, well, your observation concerning the recompression chambers is astute---I think I will stay dry and crack a beer before purposely going into decompression without a chamber.
Safety stops are good and I do them but the Navy tables do not require them, I generally stay within the tables by 10 to 20 percent, but a direct ascent is acceptable.
I fully agree with you on the bouyancy stuff and the "normal" over weighting of divers today using current methods and training.

If the operators in your area require a pony, get yourself one, rig it in a manner common to what is done in your area, I was not entirely kidding about rigging a pony as an assymtric double. N
 
John C. Ratliff:
Now, Web Monkey asked how to do an emergency swimming ascent without getting DCS? It is easy--you don't go near the "knife edge" of the no-decompression limits for Sport Diving. Web Monkey is obviously a technical diver, and there are different parameters for technical diving.

We don't do technical diving. My buddy and I are still having fun within rec limits, although there are some deeper wrecks we would like to see and will probably start tech training next year. However, we do like to minimize risks where possible.

We don't consider an ESA to be a prudent option when the other option is to carry a redundant air source and do a normal ascent.

Yes, either of us could probably do an ESA from pretty much any recreational depth. However the risks are significantly greater than doing a normal ascent from these depths, so we choose to carry a redundant air source to eliminate these risks.

The current ascent rate recommendations are based on minimizing risk to the diver. If "blow and go" were a great way to get to the surface, we'd all be doing it on every dive, since it eliminates a lot time we waste going slow.

Terry
 
John C. Ratliff:
Now, if I am at eye level on a full breath at the beginning of a dive, I will be at eye level at the end of a dive at the surface with a full exhale (I have a 5 liter vital capasity).
This makes me want to ask...

If you're eye level with a "full exhale" at the end of the dive, doesn't that mean that you're positively buoyant, even with emtpy lungs?

In other words, at the end of this dive, there is no way for you to stay down at, say, 10 feet, even with totally empty lungs (much less while breathing your 2 L tidal volume), without swimming downward. Right?
 
gentlemen,
this has been an informitive thread with lots of good participation
this summer i have signed up to take sdi's solo diver certification.
will they teach the course with the pony slung or strapped to the back?
will they teach the course using a spg?
thank you in advance
regards,
 
Nemrod:
I fully agree with you on the bouyancy stuff and the "normal" over weighting of divers today using current methods and training.

Not sure what planet you guys are living on, but I see you dive in socal and fla...

When you get down to 45 degrees F in the water or colder you're gonna want to start using a drysuit, and your SAC rate will go up. Read all the threads about divers being surprised by how much their SAC rate shoots up when they go to colder climates to dive. Big steel tanks become more useful up here, so do drysuits. The result is that you're gonna be almost 10# negative at the start of a dive becuase you don't get suit compression, and you have more swing because you carry and use more gas. If you try to start out a dive so that you're neutral with a full exhale you will wind up doing a ballistic ascent from 60 ft.

Wetsuits and AL80s or other small tanks are a whole different ballgame. Even with a drysuit and an AL80 I should *barely* be able to get down with gravity on a full exhale at the start and yet still be able to hold my stops. If you're diving wet with an AL80, I could see how swimming down at the start would be acceptable and still let you hold your stops.
 
lamont:
Not sure what planet you guys are living on, but I see you dive in socal and fla...

When you get down to 45 degrees F in the water or colder you're gonna want to start using a drysuit, and your SAC rate will go up. Read all the threads about divers being surprised by how much their SAC rate shoots up when they go to colder climates to dive. Big steel tanks become more useful up here, so do drysuits. The result is that you're gonna be almost 10# negative at the start of a dive becuase you don't get suit compression, and you have more swing because you carry and use more gas. If you try to start out a dive so that you're neutral with a full exhale you will wind up doing a ballistic ascent from 60 ft.

Wetsuits and AL80s or other small tanks are a whole different ballgame. Even with a drysuit and an AL80 I should *barely* be able to get down with gravity on a full exhale at the start and yet still be able to hold my stops. If you're diving wet with an AL80, I could see how swimming down at the start would be acceptable and still let you hold your stops.

I hear what you are saying, but it goes against my own experience with dry suits. I dove a dry suit for about ten years, an Aquala rubber dry suit, and found my surface air consumption (SAC) went down, not up, compared to diving in a wet suit in the same waters. It did so because I was warmer and more relaxed than in a wet suit. I'm posting a photo of me taken by Bruce Higgins in Clear Lake, Oregon (headwaters of the McKenzie River in the Cascade Mountains east of Eugene) in 1974 in an Aquala dry suit. I was wearing a single steel 80 tank, and double hose regulator.

So what is the difference with today's dry suits? Perhaps, you have set yourselves up for higher air consumption. See whether this scenario fits? The dry suits today are not as streamlined as the flexible rubber ones used in the 1970s (at least some are not). Since they are not as streamlined, more effort is needed to move forward. This results in more work, which results in the need for more air. So HP steel cylinders which are negative are used because they hold more air in the same package. But they also add to the work done because you add a bit of bulk and negative buoyancy, so better, bigger BCs are used. This also increases drag in the water, so work is done swimming, and more air is consumed per given time (SAC rate increased). Because of this, the diver considers doubles, and upon acquiring them, finds a further increase bulk, which leads to a bigger wing, and an increase in SAC. Basically, you set up a self-fulfilling prophesy of needing more air. But the more air you feel you need, the less streamlining and greater the drag, especially with technical divers who put on doubles, then add two slung stage bottles to boot. So you go to an underwater propulsion vehicle to carry everything.

Does this fit?

SeaRat

PS--Lamont, it seems that we agree on the breath control and basic buoyancy questions above. To answer someone else's question, slightly positively buoyant on the surface is not the same as being in the same configuration/tank pressure at ten or fifteen feet. That would be essentially neutral again. Also, I usually have some air in the tank when I surface, so it is not at its worst-case either for buoyancy.
 
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