Doubles for Intro/Basic (Cave)?

[vicp]

If one is limited when using doubles for Intro/Basic Cave training/certification to 1/6 gas to turnaround and for a max of 1 year from date of certification, what is the piont of using doubles (for cave at this level)? If one's doubles are smaller (let's say double 95s), you would actually get to use less gas before having to turn back than with a single 108.

To me it seems that it would be better to use a single (w/H or Y) for intro cave training and diving, take tech courses (adv nitrox, deco, doubles, etc.) and then take the Apprentice cave where doubles are required.

Am I missing something (other than the redundancy of 5/6 gas for exit) that would point to a benefit of doubles for intro/basic cave?

Thanks

[Oister]

When I took Intro I did it in doubles because that was what I was diving in the NE. Why change your configuration for a few extra cubic feet of gas and lose some redundancy.

[cmufieldhockey8]

More gas is a huge reason to dive doubles. You can dive 6ths on the doubles where as diving 3rds on a single tank gets you the same amount of gas but is much more risky. If you plan to continue your training past intro you might as well get the practice in doubles so when you take apprentice you are very comfortable in your gear.

[sandy]

An advantage to taking Cavern and Intro with doubles is that you would be training, diving, and working on your trim, bouyancy, skills, etc. with equipment that will take you through the remaining cave classes. Diving at the intro level is more about practicing and refining skills/techniques that you learned in class than seeing how far you can penetrate. There is plenty of cave to see while diving on 1/6. Also, NACD and NSSCDS (not sure about the others) restrict Intro to no deco. If you dive doubles from 1/6 to 1/3 you will hit deco in many caves. Remember also that 1/3 is the max you want to go whether with a single or doubles. There are many reasons why you may want to dive less than 1/3. Air consumption increases during lights out, silty conditions, and air share incidents even in a controlled class environment.

I took Intro using a single H-valve thinking I would not go any further. If I had known then what I did after completing Intro, I would have taken Intro using doubles. If you do take intro with doubles, make sure you have experience with them first as your instructor will not want to be giving instuction on diving doubles.

Good luck with your training.

[ffdiver5597]

Looking at the standards for both NACD and NSS-CDS, NACD seems like the push for single tank with the H or Y valve, where NSS-CDS teaches it more towards doubles. Am I wrong in this? Is there major differences between the basic cave cert and the intro to cave?

Its seems that if you are going to be diving in doubles for apprentice and full why not start in intro to cave also. Getting a few feet futher back in the cave doesn't really seem worth it not to get comfortable in doubles.

[rotor60driver]

Which agency has a 1 year limit on Intro/Basic? That is usually only Apprentice and that is because it is not really a cert. but a training level that is used when unable or not wanting to do a Full Cave course all at once.

LP95's with a "cave" fill to 1/6th will only be about 6ft3 or so less gas than a LP108 with a "cave" fill to 1/3rd. This is just my opinion but that extra little gas is not worth the lack of redundancy. That gas might get you 100 - 200 feet (depending on depth and SAC) further back and now you are there without the redundancy provided by twin cylinders.

Might as well start diving the way you want to be diving later on.

[cmufieldhockey8]

LP95's with a "cave" fill to 1/6th will only be about 6ft3 or so less gas than a LP108 with a "cave" fill to 1/3rd. This is just my opinion but that extra little gas is not worth the lack of redundancy. That gas might get you 100 - 200 feet (depending on depth and SAC) further back and now you are there without the redundancy provided by twin cylinders.



Agreed, And you should turn before 3rds anyway so you hardly have any more usable gas.

[flyguy199]

Which agency has a 1 year limit on Intro/Basic? That is usually only Apprentice and that is because it is not really a cert. but a training level that is used when unable or not wanting to do a Full Cave course all at once.

LP95's with a "cave" fill to 1/6th will only be about 6ft3 or so less gas than a LP108 with a "cave" fill to 1/3rd. This is just my opinion but that extra little gas is not worth the lack of redundancy. That gas might get you 100 - 200 feet (depending on depth and SAC) further back and now you are there without the redundancy provided by twin cylinders.

Might as well start diving the way you want to be diving later on.

I believe the NSS-CDS Basic Cave cert. is time limited to 18 months. The NACD Intro. to Cave cert. (in doubles) is limited to 12 months.

[sandy]

Which agency has a 1 year limit on Intro/Basic? That is usually only Apprentice and that is because it is not really a cert. but a training level that is used when unable or not wanting to do a Full Cave course all at once.

I am fairly certain that NACD has a 1 year limit on Intro if trained in doubles. I think they added the doubles option sometime in 2008. I think NSSCDS had the option first but I am not sure if they have a time limit.

[vicp]

NACD has the the max of one year limit on using doubles for intro if trained with doubles and have instructor's approval. After the doubles time period expires, you still have the intro/basic cert but only with singles. Don't know about NSS-CDS as I don't have their cave manual and and there is nothing specific that I can find on their web site.

So - the recommendation (I sort of agree with it) is to get doubles training and experience prior to taking intro/basic and do that training with doubles.

2 (or 3) more questions:

1. Is it even worthwile to configure any tanks for H or Y or simply go straight to doubles?

2. If one gets trained and comfortable with doubles, does any cavern diving (within certification limits) still need to be done with singles (If so, would having an H/Y configuration with 2 first stages be useful or even "legal")?

Thanks

[sea2summit]

Not to totally take this in a diff direction but any failures I've had with the first stage or valve I've always found out about as soon as the valve is cracked. Any other failure has been the neck o-ring during a dive (or any time it decides it's done). I really don't know why people think a H or Y valve adds any safety but that's just me so flame away.

[RN]

NACD has the the max of one year limit on using doubles for intro if trained with doubles and have instructor's approval. After the doubles time period expires, you still have the intro/basic cert but only with singles. Don't know about NSS-CDS as I don't have their cave manual and and there is nothing specific that I can find on their web site.

So - the recommendation (I sort of agree with it) is to get doubles training and experience prior to taking intro/basic and do that training with doubles.

2 (or 3) more questions:

1. Is it even worthwile to configure any tanks for H or Y or simply go straight to doubles?

2. If one gets trained and comfortable with doubles, does any cavern diving (within certification limits) still need to be done with singles (If so, would having an H/Y configuration with 2 first stages be useful or even "legal")?

Thanks

If you're planning on going all the way through cave, then get in the gear you'll be diving caves in. That can't be a single tank, so that leaves you with the option of backmounted doubles or sidemounted cylinders. Why learn the skills in a single tank if you're not going to dive in a single tank? The purpose of training and practice is to build muscle memory. Your muscle memory is going to be a little different in back or sidemount than in a single tanks.

As for the different agencies, NACD and NSS-CDS are the only agencies that have time limits on their certifications. IANTD prints "Completed in Doubles" right on the Intro card and does not have an expiration date. If you're interested in completing your training through a certain agency but don't want to be rushed to move on, find an instructor who can issue multiple certs. The course should be the same regardless of the agency you receive your certification through. I teach cave through a few different agencies and just make sure the small differences in standards are incorporated into my courses so I can issue all the certs if a student wants all of them.

I wouldn't bother setting up H or Y valves. Just go for the doubles or sidemount cylinders.

There is only one location that concerns itself with how many tanks you're diving. Every other site you go to doesn't check anything other than to see if you have a cert card. Getting into doubles or sidemount now and practicing in the cavern zone after you get comfortable with it in OW is the best way to go about it.

[350xfire]

If one is limited when using doubles for Intro/Basic Cave training/certification to 1/6 gas to turnaround and for a max of 1 year from date of certification, what is the piont of using doubles (for cave at this level)? If one's doubles are smaller (let's say double 95s), you would actually get to use less gas before having to turn back than with a single 108.

To me it seems that it would be better to use a single (w/H or Y) for intro cave training and diving, take tech courses (adv nitrox, deco, doubles, etc.) and then take the Apprentice cave where doubles are required.

Am I missing something (other than the redundancy of 5/6 gas for exit) that would point to a benefit of doubles for intro/basic cave?

Thanks

The faster you get in doubles the faster you'll get used to them!!!

[LCF]

We were talking about this the other night. On the one hand, we see so many threads saying that people are rushing further into the caves than they should be, given their experience level. Some instructors wish people would space out their classes and take their education more slowly. But you have an agency that's basically telling you you have to get through Full Cave in a year! It doesn't make sense to me.

My Cave 1 card was good forever, as long as I got 25 dives every three years. There was no pressure to go and take the next level class before I was ready.

[DA Aquamaster]

I agree, if you plan on going to full cave eventually, it makes sense to start in doubles as soon as possible. I came to cave diving after technical wreck diving, so I started cavern in doubles with the advantage of lots of time in doubles with rock solid trim and buoyancy in them. It made completing cavern and intro very easy as all the focus could be on the cave skills, not the dry suit and doubles.

Consequently, I recomend using doubles, but get comfortable in them before you show up for any class as you want toi focus on the class, not weighting, trimming and managing a new doubles configuration.

I also think it makes sense to do advanced nitrox and deco procedures either before a full cave course or concurrent with a full cave course. If you do it post full cave, do deco procedures with one of the very small number of cave instructors that teaches it with a travel gas/stage in a cave environment.

In my opinon if you are going to do doubles you need to either use a redundant wing, or a drysuit, and the drysuit makes sense on long dives with extensive deco. Again, it makes sense to get real comfortable with a dry suit before showing up for a class, and deco in a dry suit pretty much requires a pee valve to ensure you stay properly hydrated.

------

My understanding is that NSS-CDS allowed 18 months in doubles post basic cave if you trained in doubles and had the instructor's signature.

NACD did a keep up with the Jones's thing, but screwed the pooch by limiting it to 12 months rather than 18 months. Many instructors are cross certified for both so if the option exists it makes more sense to go NSS-CDS than to go NACD. In effect, adopting the shorter limit meant it did not do anythig to make the NACD sert more attractive.

The other issue is that (at least my understnnding of it) an NACD instructor cannot sign you off for doubles at the intro level if they are only an intro level instructor.

---

I agree with Lynn that limiting the use of doubles at Intro if you trained in them makes zero sense. But I think the logic is that most NSS-CDS divers will go on to become full cave. The GUE approach of cave 1 with the ability to do a limited number of jumps/navigational decisions is based on the idea that some divers may decide to never go beyond Cave 1, so it is a fundamental difference in philosophy.

That said, whether you do IANTD, NSS-CDS or NACD, I think it is a very bad idea to go straight from intro/basic to full cave. You learn a lot with a year of so of actual cave diving between intro/basic and full and the outcomes are much better in terms of skills, experience, judgment and confidence levels.

If I were king of NACD or NSS-CDS, I'd push doubles at basic/intro with no expiration date and strongly suggest 25 non training cave dives between basic/intro and full cave. I think it (along with tighter standards/better screening by instructors) would produce safer cave divers and would also hopefully reduce the number of full cave certified rototillers I see out there.

[rotor60driver]

We were talking about this the other night. On the one hand, we see so many threads saying that people are rushing further into the caves than they should be, given their experience level. Some instructors wish people would space out their classes and take their education more slowly. But you have an agency that's basically telling you you have to get through Full Cave in a year! It doesn't make sense to me.

My Cave 1 card was good forever, as long as I got 25 dives every three years. There was no pressure to go and take the next level class before I was ready.

I'm with Lynne on this one. There should be no need to rush.

Now the other part of the discussion becomes the "limitations" placed on the different levels of training. I have seen some folks posting what they think different limitations are and other folks whom I know are instructors posting what I am fairly certain some of the S&P's of the organizations say, but let's look at what we can find for "joe" diver to know what his/her limits are.

I don't have certifications from that many agencies so here is what I know. The following "limits" are written on the backs of the cards. Hopefully someone else will post from cards I don't have on here.

TDI Cavern Card "Trained to dive within the daylight zone, 200 linear ft, max depth 130ft/40ft visibility. No restrictions no deco dives. Cave diving rules of training, guideline, air management, depth & lights apply."

TDI Intro to Cave Diver "Max depth 130ft w/30ft visibility, no deco dives, no restricitons, reserve 2/3 air supply to exit, continuous guideline to exit, at least (3) battery powered lights per diver."

NACD Apprentice to Cave Diver (has expiration date) "130 feet maximum depth, 1/3 air rule, 20 feet minimum starting visibility, Simple jumps and gaps only, Limited decompression, No Stage or DPV use, Max of 1.4 ATA for working portion of dive, Max of 1.6 ATA for decompression.

TDI Full Cave Diver "Trained to cave dive to the standards of guideline, air management, depth and light rules established for safety in the overhead environment to a depth of 130ft."

NACD Cave Diving (No limitations printed on the card)

Also let's look at what some web sites say:
NSS-CDS Website
http://www.nsscds.org/test/drupal/trainingprograms

NACD Website
http://www.safecavediving.com/training.shtml

TDI Website (couldn't find anything that gave information on limitations) Can't find my manual and don't remember the exacts it gave for limitations doubles vs. singles for intro or cavern.

IANTD Website (couldn't find anything that gave information on limitations)

So where am I going with this, hmmm I forgot. Really though I know that each Instructor should be informing their students of the limits and restrictions of their training and then it is up to that person to dive within the limitations. Some organizations also post the information in their training manuals, but not all. Also do as RN said and find the Instructor you want and see if he trains for an organization that has the program you want. If you know you want to go to Full Cave then just get some experience in doubles or sidemount and do all your training in that gear.

OKAY SORRY FOR THE HIJACK! Good luck with your training.

[RN]

Here are the limitations for TDI:


Penetration is limited to one-third air rule.
Forty msw/one hundred thirty fsw maximum depth.
No gear removal in cave.
Safety and decompression stops appropriate or necessary.
Maintain a continuous guideline.
Proper cave diving equipment is used.

Here are the limitations for IANTD:


In most cases, no dives may be conducted to depths greater than 130 fsw. When conditions warrant it Cave Diver Programs may be conducted to a maximum depth of 160 fsw, provided the students are qualified as Advanced Recreational Trimix or Technical Diver.

Oxygen partial pressure may not exceed 1.4 ATA during the working portion of the dives, nor exceed 1.6 ATA during the decompression portion of the dives.

There's more to the IANTD limitations, but those are the main ones that fit within this topic.

[rcpalmer1]

If one is limited when using doubles for Intro/Basic Cave training/certification to 1/6 gas to turnaround and for a max of 1 year from date of certification, what is the piont of using doubles (for cave at this level)?

I am new to the cave side of diving like the OP. I have/had the same question. I think the seasoned cave divers are missing what he is saying.

I have been deco certified with doubles for years. I have been diving in the ocean not caves. I have looked at a few different agency standards.

According to NSS which I think the OP is referring to, if I used my double 100's I could only use 1/6 of my air or 33cf. If I used a single 120 I could use 1/3 or 40cf. I would preferred to use my doubles for the extra safety but since bringing the extra 80cf of air would actually decrease my usable air 7cf the single tank is the better choice to increase bottom time. I think this is the point vicp was trying to make. Why carry an extra 40lb tank if it is only going to shorten your dive.

The answer I have heard that makes the most since to me is that they are trying to limit your penetration. When they made the standard they were probably thinking of a person using a single or a set of doubles using the same size tanks. Standards are what the agency thinks is the best way to keep every diver safe on every dive. They may not make the most since in every circumstance but if you follow them they will keep you safe.

Just my 2 cents

[sskasser]

I am new to the cave side of diving like the OP. I have/had the same question. I think the seasoned cave divers are missing what he is saying.

I have been deco certified with doubles for years. I have been diving in the ocean not caves. I have looked at a few different agency standards.

According to NSS which I think the OP is referring to, if I used my double 100's I could only use 1/6 of my air or 33cf. If I used a single 120 I could use 1/3 or 40cf. I would preferred to use my doubles for the extra safety but since bringing the extra 80cf of air would actually decrease my usable air 7cf the single tank is the better choice to increase bottom time. I think this is the point vicp was trying to make. Why carry an extra 40lb tank if it is only going to shorten your dive.

The answer I have heard that makes the most since to me is that they are trying to limit your penetration. When they made the standard they were probably thinking of a person using a single or a set of doubles using the same size tanks. Standards are what the agency thinks is the best way to keep every diver safe on every dive. They may not make the most since in every circumstance but if you follow them they will keep you safe.

Just my 2 cents

Great first post! Welcome aboard, lil bro!

[rcpalmer1]

Great first post! Welcome aboard, lil bro!

I was going to keep that a secret!!! Now I will be I will be expected to hangout with the smart kids like you.

[d_berman]

Have you taken your cavern and intro class yet?
Are you currently diving doubles ?

If you aren't currently in doubles, then taking the class in a single tank may be a good idea. Much better than throwing on a set of doubles and trying to take the class right away as it does potentially take some time to get used to them.

If you are active and comfortable in doubles then as many others seem to suggest, dive them.

Just enjoy the dives and don't fuss too much about "lost distance". There is lots to see, fun to be had and experience to be taken in.

There may be a tendency to look at the "extra gas" as a waste; try to look at it as a bonus to have so much extra and a thank goodness you didn't need it. Worst case scenario, surface talk the dive over with your buddy and do it again (possibly getting a little further).

Dave

If one is limited when using doubles for Intro/Basic Cave training/certification to 1/6 gas to turnaround and for a max of 1 year from date of certification, what is the piont of using doubles (for cave at this level)? If one's doubles are smaller (let's say double 95s), you would actually get to use less gas before having to turn back than with a single 108.

To me it seems that it would be better to use a single (w/H or Y) for intro cave training and diving, take tech courses (adv nitrox, deco, doubles, etc.) and then take the Apprentice cave where doubles are required.

Am I missing something (other than the redundancy of 5/6 gas for exit) that would point to a benefit of doubles for intro/basic cave?

Thanks

[Slüdge]

A few stray points:

If you're not proficient in doubles, take cavern in a single. You will learn more different skills in cavern than any other diving course, not including open water. It's hard to concentrate on a bunch of new skills while at the same time learning doubles.

You don't have to learn doubles in a cave. There's this great new invention, called "open water." Get totally comfortable in all facets of doubles THERE, before taking them into the caves. The caves would appreciate it.

If you're trying to figure out how to get a few extra feet of penetration (1/6 of double 95s vs. 1/3 of a single 104), you need to step back and look at the big picture. Slow down and stop sucking air like a Hoover. I can go from Peacock 1 to the Peanut Restriction on less than 1/6 of double 80s. Go slow!

Now go out there and enjoy yourself! This is play, not work.

[vicp]

I have taken cavern twice, 10 years ago with NSS-CDS and 2 months ago with NACD as a refresher. I have cavern certifications from both and did both classes with a single tank.

As I seem to have gotten the bug for for overhead and technical (not necessarily very deep or extended deco), I am looking towards getting more overhead experience and training and intro/basic cave seems to be the next step. Even though I have been diving for over 30 years (just about all ocean) and am a Divemaster, I am fairly new to overhead (~20 dives) and have never used doubles.

Looking at the cave requirements and limitations made me ask the original question about whether it made sense to use doubles for intro/basic cave given the restrictions (1/6 gas, time limits, etc.) specified by NSS and NACD.

After thinking about what everyone has said, I think that I will just get more experience with my newly acquired dry suit and double up my LP108s in the very near future and possibly take a Tech (doubles?) class so that I get very comfortable with all the new gear before taking inro/basic cave. I may also try to find a certifying agency (IANTD, others?) that does not time limit doubles use for intro/basic cave.

BTW, is there a doubles restriction for cavern? NACD says 1/6 and under instructor supervision. What about after the class?

My NSS-CDS cavern manual from the time I took the cavern class 10 years ago (First Printing, 1988 ), discusses singles, doubles, K, J, Y (dual) valves and manifolds but does not mention anything about using only singles or any doubles restrictions. They only recommend that team members use the same size cylinders filled to the same pressure.

I take this to mean that if I feel comfortable and competent in doubles, I can dive them legally in cavern zones with my NSSCDS cert. Is this correct?

Thanks

[rotor60driver]

According to NSS which I think the OP is referring to, if I used my double 100's I could only use 1/6 of my air or 33cf. If I used a single 120 I could use 1/3 or 40cf. I would preferred to use my doubles for the extra safety but since bringing the extra 80cf of air would actually decrease my usable air 7cf the single tank is the better choice to increase bottom time. I think this is the point vicp was trying to make. Why carry an extra 40lb tank if it is only going to shorten your dive.



Welcome aboard! This is exactly what I was saying in my previous post. You are only talking about 7cf more with less redundancy. You will only increase bottom time by minutes and distance by a short distance in most Florida caves. I am not saying to go out and try new gear first thing in a cave but instead of doing any cave training in a single get the doubles experience in OW (like Sludge posted). I don't have issue with singles for cavern diving though so get lots of experience running lines and dealing with flow and such in the cavern zone.

Most of all Have FUN!

[tflaris]

If one is limited when using doubles for Intro/Basic Cave training/certification to 1/6 gas to turnaround and for a max of 1 year from date of certification, what is the piont of using doubles (for cave at this level)? If one's doubles are smaller (let's say double 95s), you would actually get to use less gas before having to turn back than with a single 108.

To me it seems that it would be better to use a single (w/H or Y) for intro cave training and diving, take tech courses (adv nitrox, deco, doubles, etc.) and then take the Apprentice cave where doubles are required.

Am I missing something (other than the redundancy of 5/6 gas for exit) that would point to a benefit of doubles for intro/basic cave?

Thanks

Diving in doubles in in my opinion significantly different than single tank configuration. Regardless of the gas that can be used on any single dive you would be preparing yourself for apprentice and full cave.

Good Luck

[skip]

If one is limited when using doubles for Intro/Basic Cave training/certification to 1/6 gas to turnaround and for a max of 1 year from date of certification, what is the piont of using doubles (for cave at this level)? If one's doubles are smaller (let's say double 95s), you would actually get to use less gas before having to turn back than with a single 108.

To me it seems that it would be better to use a single (w/H or Y) for intro cave training and diving, take tech courses (adv nitrox, deco, doubles, etc.) and then take the Apprentice cave where doubles are required.

Am I missing something (other than the redundancy of 5/6 gas for exit) that would point to a benefit of doubles for intro/basic cave?

Thanks

Using less or more gas is not really an issue in cavern/intro. You get in, do your drills, get out and do it again. With doubles you can do two dives before needing a fill (that's a benefit). For Decompression Techniques, NAUI requires doubles (intro to tech, adv nitrox, can be done with H-valve single), and as other's have said at some point you will want doubles anyway. so why not start with doubles? one good reason is that you want to take the cavern/intro course now and not after spending more money for more gear and spend the time in open water getting used to it.

The gas differential is a nonissue, but the other things are worth considering.

skip

[willardj]

I am like many. I did my Cavern in doubles waited a year them did Basic in doubles. I have had no problem diving 1/6. I have 95's and a good sac rate too. I have made it from P-1 to Olsin on 1/6's. I did about 75 dives at cavern and lil over 110 at Basic lvl.

The main thing to think of is don't worry about how far you can go. Spend most of your time on skills and proficiency. You will be amazed how quick things will come. Then it want matter how much gas you have on your back. :) There is so much to see at these lvl's. Have fun

[DA Aquamaster]

If you're trying to figure out how to get a few extra feet of penetration (1/6 of double 95s vs. 1/3 of a single 104), you need to step back and look at the big picture. Slow down and stop sucking air like a Hoover. I can go from Peacock 1 to the Peanut Restriction on less than 1/6 of double 80s. Go slow!Sludge is correct - focusing on pentration is a mistake and misses several of the larger issues.

In my opinion, too many divers focus on pentration distance and on artificially reducing their SAC rate. Swimming fast uses more O2 - swimming twice as fast requires 4 times the energy and burnes 4 times the O2. Also, each liter of O2 metabolized generates .92 liters of CO2 and CO2 is the thing that triggers the urge to breathe. So..swimming faster greatly increases SAC - far out of proportion to any increase in speed. Divers try to "cheat" by skip breathing and artifically reducing the num ber of respirations per minute. But that means they exhale less often and consequently retain CO2.

Higher CO2 increases the urge to breathe, dialates blood vessels (and can give you a killer headache), exacerbates nitrogen narcosis and has been implicated in greater suceptibility to oxygen toxicity. All of it is bad.

The problem is that the focus on pentration in conjunction with agency efforts to limit pentration by limiting them to 1/6th in doubles and 1/3rds in a single creates a situation where an intro diver is more or less encouraged to skip breathe, etc to improve their penetration distance - rather than just relaxing slowing down and letting that reduce their SAC rate and in turn increase their distance.

[Michael Stroeck]

Sludge is correct - focusing on pentration is a mistake and misses several of the larger issues.

In my opinion, too many divers focus on pentration distance and on artificially reducing their SAC rate. Swimming fast uses more O2 - swimming twice as fast requires 4 times the energy and burnes 4 times the O2. Also, each liter of O2 metabolized generates .92 liters of CO2 and CO2 is the thing that triggers the urge to breathe. So..swimming faster greatly increases SAC - far out of proportion to any increase in speed. Divers try to "cheat" by skip breathing and artifically reducing the num ber of respirations per minute. But that means they exhale less often and consequently retain CO2.

Higher CO2 increases the urge to breathe, dialates blood vessels (and can give you a killer headache), exacerbates nitrogen narcosis and has been implicated in greater suceptibility to oxygen toxicity. All of it is bad.

The problem is that the focus on pentration in conjunction with agency efforts to limit pentration by limiting them to 1/6th in doubles and 1/3rds in a single creates a situation where an intro diver is more or less encouraged to skip breathe, etc to improve their penetration distance - rather than just relaxing slowing down and letting that reduce their SAC rate and in turn increase their distance.

:clapper High flow? Swim smart and slow!

[RN]

I have taken cavern twice, 10 years ago with NSS-CDS and 2 months ago with NACD as a refresher. I have cavern certifications from both and did both classes with a single tank.

As I seem to have gotten the bug for for overhead and technical (not necessarily very deep or extended deco), I am looking towards getting more overhead experience and training and intro/basic cave seems to be the next step. Even though I have been diving for over 30 years (just about all ocean) and am a Divemaster, I am fairly new to overhead (~20 dives) and have never used doubles.

Looking at the cave requirements and limitations made me ask the original question about whether it made sense to use doubles for intro/basic cave given the restrictions (1/6 gas, time limits, etc.) specified by NSS and NACD.

After thinking about what everyone has said, I think that I will just get more experience with my newly acquired dry suit and double up my LP108s in the very near future and possibly take a Tech (doubles?) class so that I get very comfortable with all the new gear before taking inro/basic cave. I may also try to find a certifying agency (IANTD, others?) that does not time limit doubles use for intro/basic cave.

BTW, is there a doubles restriction for cavern? NACD says 1/6 and under instructor supervision. What about after the class?

My NSS-CDS cavern manual from the time I took the cavern class 10 years ago (First Printing, 1988 ), discusses singles, doubles, K, J, Y (dual) valves and manifolds but does not mention anything about using only singles or any doubles restrictions. They only recommend that team members use the same size cylinders filled to the same pressure.

I take this to mean that if I feel comfortable and competent in doubles, I can dive them legally in cavern zones with my NSSCDS cert. Is this correct?

Thanks

All of the training agencies limit penetration to 1/6 of doubles, 1/3 of single at the intro/basic level. The purpose of intro/basic is to learn new skills in a new environment while keeping you somewhat close to the exit point with lots of air. Of course, that's all in perspective. I have done 2000' + penetrations before hitting 1/6s. It just depends on the depth of the system. All of the agencies I'm familiar with limit cavern diving to 1/3s of usable gas. None of them differentiate between doubles or single. And since you're penetration is limited to 200' linear from OW, turn pressure will not limit your penetration distance. At the level you are at, the best thing to do would be get into a set of doubles, or try sidemount, in OW. Get comfortable in the double tank set up then start venturing into caverns you are familiar with. Once you're comfortable there, move onto intro/basic. Don't worry about the agency. They are all pretty similar. There are minor differences in standards, but not enough to make any of the courses that different. In fact, the courses I teach incorporate the standards from all the agencies I teach for so I can issue certs from all of them if the student desires all of them. It's a lot easier than changing my course depending on what card I'm issuing. You can save yourself some time in the transition to doubles/sidemount by taking a course. A good course can save you 2-3 dozen dives of tweaking, but you'll still need a dozen or so dives after that to get more comfortable in the new configuration. Finally, look at the 1/6 limitation this way...you can do 2 dives off of one fill. This saves you money and saves you time running back to the fill station.

[rox@ucf11]

We were talking about this the other night. On the one hand, we see so many threads saying that people are rushing further into the caves than they should be, given their experience level. Some instructors wish people would space out their classes and take their education more slowly. But you have an agency that's basically telling you you have to get through Full Cave in a year! It doesn't make sense to me.

My Cave 1 card was good forever, as long as I got 25 dives every three years. There was no pressure to go and take the next level class before I was ready.

The way it seems to me with intro in doubles and a time limit is the understanding that if you do an intro course in doubles, you will eventually be continuing your training. If you decide later that intro is as far as you want to go, you still have the singles/intro card.

[LCF]

So, I trained in doubles, I've been diving caves for a year in doubles, and all of a sudden, I can't do it any more? It just doesn't make sense, but maybe in part that's because I think doubles are a darned good idea in a cave, and since I dive primarily in Mexico, sixths allows a lot of really pretty, fun diving. I could see someone who just doesn't get to do that many cave diving trips being satisfied at Intro for a long time.