50 replies to this topic

[intotheblue]

I’m considering taking the plunge toward more Tech-oriented diving. Among the gear considerations is
diving doubles. So, my first question is how big should a beginners setup be in terms of tank size? And should I look at aluminum or steel?

I know that if I start getting into large steel tanks that I would have to dive dry due to weight issues and wing size but what about diving wet? What's the max size I should look at?

are there other considerations, too?

Hey FG... long time! haven't read the whole thread, so pardon if I tread where others have been... but the main things I would first consider are what are the intentions or needs for diving doubles and who will you be diving with and what are they using? Do you need more gas or do you need redundancy? Are you diving with an "air hog"? Are YOU an air hog??? (not likely, but to be considered by anyone making such decisions). Understanding your real motivations for diving doubles will help you to make a wiser and less costly choice. I was big into cave and wreck diving up until a couple years ago, now I haven't been in a cave or wreck in almost two years. I have split some of my doubles into singles for use offshore with "H" valves to achieve redundency, needing less extra air than when cave or wreck diving. You might achieve your need by starting with a single with "H" valve and later adding another with an isolator for a doubles set-up. Less investment up front, and less hassle than toting around a set of doubles. Some boat owners don't really like to see doubles on their boats (they tend to create more wear and tear) and you may be more limited than you have considered. When I started in doubles, my goal was training and equiping to dive the Andrea Doria, a five year goal. I knew I wanted to dive cave and had cave diving friends that I would be diving alot with in Florida, so getting set up with doubles pretty quickly made sense for me. However, before I did that, I bought a pair of steel 95's to use while teaching classes as singles. They quickly became my first set of doubles. Being in a cave, my weight issues were not as critical, as I dove dry for redundant buoyancy. Diving "wet" in open water where you may have a long distance to the surface that you cannot get to if bouyancy is lost (some say you can crawl out of a cave if you have to, although I'd hate to rely on that), wearing heavy tanks is discouraged, thinking being you should be able to swim any tanks you wear to the surface when in open water. There are other means for achieving redundant buoyancy, but extra wings and extra-large wings create more drag and air trapping hazards. The issue can become more complex than you might imagine, so knowing what your diving intentions are really helps choose the right equipment, while saving money in the long run.

I hope you have lots of experience, and that you enjoy your expansion into "more technical" diving. Your potential task loading goes up significantly, but your equipment to handle any emergency, once you become accustomed to it, will mitigate most of the problems once you have the training and gain more experience with it. Sheck used to say... there's not a problem in diving you can't handle, if you have enough "air" (gas). That is mostly true, but there are a couple problems even air won't solve!

ITB--

[captsteve]

perone..... you need about a third "more" weight in salt water. that more than compensates for some set-ups. however, its also important to note that there are lots of options for both steel and aluminum tanks. some low pressure steel tanks are actually neutral when empty( at least they are advertised that way). i will try to get links together to post.....if i dont loose my internet connection again!

[Dive_buddy]

One picture is worth a thousand words.



The yellow one on the left is an AL 80, the red one on the right is an HP 80.

Here is a link to a site with some specifications for some of the more popular tanks.
SCUBA Cylinder Specifications

Below is an exscript from a that list.

..........................................................Alum................St
eel
Manufacturer & Nominal Capacity......Catalina C80.....Faber 80
Service pressure psi..........................3300.................3180 +10%
Actual air capacity, ft3...........................77.4...................80
Outer diameter, in...................................7.25...................7.25
Length without valve, in........................25.1...................19.99
Empty weight, lbs (w/o valve)...............34.4...................32.5
Buoyancy Empty, lbs (w/valve)...............-7.22.................-0.2
Buoyancy Full, lbs (w/valve).................-13.22.................-5.9

As you can see the steel tank is more compact. Which is best? I can not answer that for you. I wear a 7mil F/J that has 26 pounds of lift on it's own. For me, HP tanks are a Godsend. If I only wore a 3mil shorty, I might follow PerroneFord's train of thought and want the buoyancy of Aluminum tanks.

If you are thinking of getting to Tech diving, I would recommend that you get together with your potential dive buddies and ask them. As I understand the DIR concept, everyone has the exact same gear with the exact same set up (saves on confusion in a tight spot). They may be able to steer you in the right direction so that your beginner tanks can be used as your veteran tanks as well.

Hope the pics and the link help.

[PerroneFord]

One picture is worth a thousand words.

Below is an exscript from a that list.

..........................................................Alum................St
eel
Manufacturer & Nominal Capacity......Catalina C80.....Faber 80
Service pressure psi..........................3300.................3180 +10%
Actual air capacity, ft3...........................77.4...................80
Outer diameter, in...................................7.25...................7.25
Length without valve, in........................25.1...................19.99
Empty weight, lbs (w/o valve)...............34.4...................32.5
Buoyancy Empty, lbs (w/valve)...............-7.22.................-0.2
Buoyancy Full, lbs (w/valve).................-13.22.................-5.9

I've never even seen a Catalina 80. Everyone I know has Luxfers. Generally Catalina's are known to have poor buoyancy characteristcs and ride poorly as they empty.

As I understand the DIR concept, everyone has the exact same gear with the exact same set up (saves on confusion in a tight spot). They may be able to steer you in the right direction so that your beginner tanks can be used as your veteran tanks as well.

Ummm, not exactly. All DIR setups are not exactly the same and often with good reason. The same basic gear is the same, but with variances for things like SAC rates, photography/video, team captains, bag man, reel man, etc.

GUE recommends AL80s for ocean diving, and generally matching steel tanks for overheads. So if you want to go DIR, get AL80s for the ocean, and match your gear to your team for other kinds of diving.

[6Gill]

One picture is worth a thousand words.



The yellow one on the left is an AL 80, the red one on the right is an HP 80.

Here is a link to a site with some specifications for some of the more popular tanks.
SCUBA Cylinder Specifications

Below is an exscript from a that list.

..........................................................Alum................St
eel
Manufacturer & Nominal Capacity......Catalina C80.....Faber 80
Service pressure psi..........................3300.................3180 +10%
Actual air capacity, ft3...........................77.4...................80
Outer diameter, in...................................7.25...................7.25
Length without valve, in........................25.1...................19.99
Empty weight, lbs (w/o valve)...............34.4...................32.5
Buoyancy Empty, lbs (w/valve)...............-7.22.................-0.2
Buoyancy Full, lbs (w/valve).................-13.22.................-5.9

As you can see the steel tank is more compact. Which is best? I can not answer that for you. I wear a 7mil F/J that has 26 pounds of lift on it's own. For me, HP tanks are a Godsend. If I only wore a 3mil shorty, I might follow PerroneFord's train of thought and want the buoyancy of Aluminum tanks.

If you are thinking of getting to Tech diving, I would recommend that you get together with your potential dive buddies and ask them. As I understand the DIR concept, everyone has the exact same gear with the exact same set up (saves on confusion in a tight spot). They may be able to steer you in the right direction so that your beginner tanks can be used as your veteran tanks as well.

Hope the pics and the link help.

Just to clarify the tanks in the picture are not the ones listed in the specs below the picture.When comparing the two tanks with capacity being approx the same the height of the tank is being shorter is not always better.At 5'10" I find the Genisis 80(short tank in the pic) sits high up on my back causing a head heavy condition when in horizontal trim which I need to offset.Also not easy to see in the picture is that the tanks use valves of differnet tank neck dia. so avalibility of valves and interchangibility might be an issue.It is important to consider the total weight shift from a full tank to empty.High pressure tanks tend to have a greater weight change.If your looking at diving nitox or trimix where and how you get fills should be thought about.Low pressure tanks are easier to fill when using partial pressure filling.Also cheaper if your doing your own fills.
As Dive Buddy pointed out if diving with a group a common tank size has a couple advantages.The first is ease of gas planning on a dive(math is easier) and also for sharing of tanks(going away?borrow a set from someone in the group not going,no need to change anything or do calculations with a different set of numbers)
It is really hard to just say "theses are the tanks you need" as there are alot of varibles(as people have brought up) and you need to figure out what's important.The thing to remember unless you buy some odd ball tank you can always sell it but (using myself as an example) I have tanks ranging from 30cuft to 130cuft in that I use granted some more oftenm then others.Plus I'm still on the look out for more tanks if I can get a good deal.

Eric

I've never even seen a Catalina 80. Everyone I know has Luxfers. Generally Catalina's are known to have poor buoyancy characteristcs and ride poorly as they empty.

This is more an issue when using the tanks(both the 40 and 80) as deco/stage bottles.When used as back gas not as noticable but if your going to buy tanks might as well get the ones that work better in more applications.

Eric

[captsteve]

One picture is worth a thousand words.



The yellow one on the left is an AL 80, the red one on the right is an HP 80.

Here is a link to a site with some specifications for some of the more popular tanks.
SCUBA Cylinder Specifications

Below is an exscript from a that list.

..........................................................Alum................St
eel
Manufacturer & Nominal Capacity......Catalina C80.....Faber 80
Service pressure psi..........................3300.................3180 +10%
Actual air capacity, ft3...........................77.4...................80
Outer diameter, in...................................7.25...................7.25
Length without valve, in........................25.1...................19.99
Empty weight, lbs (w/o valve)...............34.4...................32.5
Buoyancy Empty, lbs (w/valve)...............-7.22.................-0.2
Buoyancy Full, lbs (w/valve).................-13.22.................-5.9

As you can see the steel tank is more compact. Which is best? I can not answer that for you. I wear a 7mil F/J that has 26 pounds of lift on it's own. For me, HP tanks are a Godsend. If I only wore a 3mil shorty, I might follow PerroneFord's train of thought and want the buoyancy of Aluminum tanks.

If you are thinking of getting to Tech diving, I would recommend that you get together with your potential dive buddies and ask them. As I understand the DIR concept, everyone has the exact same gear with the exact same set up (saves on confusion in a tight spot). They may be able to steer you in the right direction so that your beginner tanks can be used as your veteran tanks as well.

Hope the pics and the link help.

Just to clarify the tanks in the picture are not the ones listed in the specs below the picture.When comparing the two tanks with capacity being approx the same the height of the tank is being shorter is not always better.At 5'10" I find the Genisis 80(short tank in the pic) sits high up on my back causing a head heavy condition when in horizontal trim which I need to offset.Also not easy to see in the picture is that the tanks use valves of differnet tank neck dia. so avalibility of valves and interchangibility might be an issue.It is important to consider the total weight shift from a full tank to empty.High pressure tanks tend to have a greater weight change.If your looking at diving nitox or trimix where and how you get fills should be thought about.Low pressure tanks are easier to fill when using partial pressure filling.Also cheaper if your doing your own fills.
As Dive Buddy pointed out if diving with a group a common tank size has a couple advantages.The first is ease of gas planning on a dive(math is easier) and also for sharing of tanks(going away?borrow a set from someone in the group not going,no need to change anything or do calculations with a different set of numbers)
It is really hard to just say "theses are the tanks you need" as there are alot of varibles(as people have brought up) and you need to figure out what's important.The thing to remember unless you buy some odd ball tank you can always sell it but (using myself as an example) I have tanks ranging from 30cuft to 130cuft in that I use granted some more oftenm then others.Plus I'm still on the look out for more tanks if I can get a good deal.

Eric

steel tanks come in other dimensions, but are usually of much less volume........not nec shorter....i think that was the point. it has become clear to me that some people just prefer al while others prefer steel. i would rather be just slightly negative on the tank while others would prefer to be more positive. i also agree that depending on the diving you are doing, you can fine tune..................a faber 85lp is -neutral- empty but 6.0 + full. a 72 2250 is -3neg empty.
i prefer the steel because there is less drag in the current i dive in. the current is far more dangerous than tank weight.

[Dive_buddy]

Okay, I can see it's “Disclaimer time”!!

You guys remind me of a friend of mine. He is a Buyer for a local chain store. His job is to buy sweaters from manufacturers to sell in the stores. Yup, he is a knit picker too.

Anyway, the picture was for an example, just to show the size difference in tanks of the same, approximate volume. As for not hearing about a Cat-80, I wouldn't know from shinolla. All my tanks are Sherwoods except for my Cat-30 pony bottle.

The exscript was simply to show some of the differences in tank stats. As the site says, the list is not all inclusive and may contain errors. But it is still a very good resource when looking at tanks. I used it when looking for my first tanks. And if you noticed, Sherwood is not even on the list. It's a guide, not a gospel.

Eric, did you just not mention it, or did you fail to notice? The big yeller one is a Yoke fitting and the short little feller is DIN. By the way, the AL-80 is part of my save-a-dive kit. When a dive buddy does not have a tank or a full tank for that last dive of the day, out it comes.

And I agree about the 80s. They mess up your trim something fierce! I normally dive HP-100s. I use the 80 only when my 100s are used, or if I'm with a new (read “that I don't know) dive buddy. I know we ain't staying down long enough for me to use the 100 up. But it will be too low to use on a second dive. So I use the 80s. But then I have to shift weight around, my trim is off and it's an ugly, ugly, ugly thing.

Once again, I have enjoyed this thread. And must give proper credit to the originator for this thread. To her, I most sincerely say:

Tanks!

[ScubaGypsy]

GUE recommends AL80s for ocean diving, and generally matching steel tanks for overheads. So if you want to go DIR, get AL80s for the ocean, and match your gear to your team for other kinds of diving.

In my GUE-Fs class it was recommended to use Al80s in the ocean for wetsuit diving but to use steel doubles for drysuit diving in the ocean and in freshwater.

[PerroneFord]

In my GUE-Fs class it was recommended to use Al80s in the ocean for wetsuit diving but to use steel doubles for drysuit diving in the ocean and in freshwater.

And I have a photo of your Fundies instructor making a dive in the Torgugas, on the Araby Maid. Proudly wearing his TLS350, AL80 doubles, and two Al40s for deco bottles.

The idea here is not whether to dive steel or aluminum. It's about diving a "balanced setup" Yes, you can dive steel tanks in the ocean, even wet. If you normally wear a 7mm suit and 30 pounds of weight, The a pair of steel 130s will STILL give you some ditchable weight to wear in the ocean. Just be sure you can swim them up and get yourself slightly positive in the water. Remember that neutral at the surface means your mouth is underwater (eyes at water level). So you better be able to tread water a while, or have plenty of gas in your tanks. My *PERSONAL* feeling is that I want to be about 4-8 pounds postitive at the end of a dive. or with a loss of my wing. I am not a strong swimmer and not that fit. So the right choice for *ME* is one where my setup helps keep me alive.

I would LOVE to dive a set of 104s in the ocean. I could drop my weights, and my trim would be excellent without me having to have the V-weight or weightbelt I have to use with my Al80s. But until I get a lot more fit, and become a lot better swimmer, and I get a drysuit, this is just not going to happen for me. I apologize if I have offended anyone by offering my opinions here, maybe stronger than I should. I would simply HATE to see anyone get into real distress moving to doubles because they didn't consider the safety factors. It's clear that the divers here are thinking about what they are doing, so I'll shut up now on this thread.

Thanks,

-P

[6Gill]

Eric, did you just not mention it, or did you fail to notice? The big yeller one is a Yoke fitting and the short little feller is DIN. By the way, the AL-80 is part of my save-a-dive kit. When a dive buddy does not have a tank or a full tank for that last dive of the day, out it comes.

Hi there Dive Buddy,
My refrence was in refrence to the thread size in the tank neck...there are 2 in North America. A 3/4" and a 5/8".You can get 3/4" in both DIN and yoke but the 5/8" is only avalible in DIN.THis would limit the avalibility of valve options on tanks using the 5/8" neck size.The 203Bar manifold also allows you to easily use DIN/yoke by the use of a screw in insert.
I'm sorry if you felt I was nit picking your post as that is not what I had in mind.I did not think you felt that the picture and the chart were related but was more concerned that others with less knowlage/experiance with tanks might draw a wrong conclusion.I for one do look foward to your post
Tanks are something that people take for granted usually concerned with capacity(which doesn't always match the said number),is it DIN/yoke and steel/aluminium.There are books written devoted to tanks,their markings,cre of ect.Alot of people don't give them the respect considering the potential for damage that a tank is capable of.

Eric

[6Gill]

I apologize if I have offended anyone by offering my opinions here, maybe stronger than I should. I would simply HATE to see anyone get into real distress moving to doubles because they didn't consider the safety factors. It's clear that the divers here are thinking about what they are doing, so I'll shut up now on this thread.

Thanks,

-P

Perrone,
I don't think an aplogy is needed and the whole reason for this thread is the sharing of knowlage,ideas and opinions. Ultimatly we decide for ourselves how we use the information but if it's not out there we don't have that option.As long as things do not become an attack on the person but a disscusion on the pro/cons of the idea and most things have strengths and weaknesses so I look foward to your input on this and other threads.

Eric

[intotheblue]

...
The idea here is not whether to dive steel or aluminum. It's about diving a "balanced setup" Yes, you can dive steel tanks in the ocean, even wet. If you normally wear a 7mm suit and 30 pounds of weight, The a pair of steel 130s will STILL give you some ditchable weight to wear in the ocean. Just be sure you can swim them up and get yourself slightly positive in the water. Remember that neutral at the surface means your mouth is underwater (eyes at water level). So you better be able to tread water a while, or have plenty of gas in your tanks. My *PERSONAL* feeling is that I want to be about 4-8 pounds postitive at the end of a dive. or with a loss of my wing. I am not a strong swimmer and not that fit. So the right choice for *ME* is one where my setup helps keep me alive.

I would LOVE to dive a set of 104s in the ocean. I could drop my weights, and my trim would be excellent without me having to have the V-weight or weightbelt I have to use with my Al80s. But until I get a lot more fit, and become a lot better swimmer, and I get a drysuit, this is just not going to happen for me. I apologize if I have offended anyone by offering my opinions here, maybe stronger than I should. I would simply HATE to see anyone get into real distress moving to doubles because they didn't consider the safety factors. It's clear that the divers here are thinking about what they are doing, so I'll shut up now on this thread.

Thanks,

-P

Of course if you're diving doubles in the ocean, you're probably in need of some serious deco. 4-8 lbs positive at the end of a dive could make it hard to stay at deco depth. Diving wet, at a depth of 100' would give roughly 1/4 the buoyancy as when you were neutral at the surface... and less at greater depths. It is tougher to swim up "overweighted" tanks than you might think, especially if you're not "that fit" (I am speaking generally here for the benefit of un-trained/inexperienced "doubles divers", and not directly pointed to this post).

I have dived OW "wet" with double 104's and don't recommend it. It's a lot of weight. Try Fabre 108's (OMS sells). They have better characteristics for OW and weight can be added if needed.

There may be other mitigating factors to consider, but using aluminum in OW while "wet" is generally considered the way to go. Another factor with Aluminum 80's, they are easier and cheaper to come by. Make all weight additions (ss backplate, v-weight, etc.) with careful considerations as to what will happen to buoyancy at the depth you could find yourself. I did "practice set-up" dives at Lake Travis in Texas in an area where I could crawl to the surface if needed, then adjusted weighting to make sure I could make it to the surface and still stay submerged for deco. Swimming 200 feet straight up with an un-ditchable excess weight can be very tiring.

Another factor to consider here is that we are seeing people with less and less experience move into technical diving. Well, even very experienced divers may not have the real judgement to understand all of these concerns unless they are really exposed to them or experience them in a quality training setting. I realize that divers of all experience levels read these posts, so please seek out a good professional with the appropriate credentials and experience to guide you, and use common sense and other resources (like diving forums) to check what you are told. Who was it that said... "trust, but verify"? Also, realize that it is very difficult to provide comprehensive answers to questions asked on the i-net, and sometimes even in person. Make sure you understand an answer before you act on it.

--

[gcbryan]

If someone can show me how to do the multi-quotes it would make life easier.

Just a few points/mistakes?/questions about this thread.

Mention was made somewhere in the thread about checking the shift full to empty for an individual tank. I just want to point out in case it's not obvious that the shift itself doesn't depend on the tank but rather how much gas the tank holds. Air weighs the same whether it's in an aluminum or a steel tank. The shift will be about 6 lbs for 80 cu ft. whether the tank is aluminum or steel. However the starting point will be different with steel being more negative and aluminum less so but the shift due to using up air will be the same. In most cases however steel tanks are larger and therefore hold more air since you rarely see aluminum tanks larger than 80 cu ft.

Just to elaborate on steel tanks of equal size being lighter than aluminum (counter-intuitive), it's because steel is much stronger than aluminum and therefore the tank walls don't need to be as thick (as aluminum) for the same strength.

Perrone, you mentioned that more weight was needed in fresh water when correcting Capt. Steve but then in the next sentence you say that when you go to salt water you use more? I'm guessing that this was just an oversight but I just want to mention this so everyone is on the same page. I know some mainly dive in fresh water and some mainly in salt water so it is possible that not everyone has had to think about these things so that's the only reason I'm bringing this up. Fresh water = less weight.

I have a question regarding those talking about making sure one can swim a steel tank up after a BC failure and it being easier with an aluminum tank. Unless you are talking about ditching your weight belt it should be the same shouldn't it? And if you are talking about ditching your weight belt then swimming up would be the least of your problems. I'm confused here. Steel tanks take more weight off of your weight belt but it goes right to your back. The weight is the same unless you are talking about ditching the weight belt. Help me out here.

I'm also a little confused about what Perrone is describing regarding liking to have all that positive buoyancy at the surface/tanks getting a little floaty at 1,000 psi, etc. What if you breath your tanks down to whatever your minimum is and are trying to hold a stop at 10 fsw?

Also, there was something mentioned about one's drysuit flooding and having to take it off to avoid sinking down to the bottom. Remember water is neutrally buoyant. If you completely flood your drysuit you do not take it off.

I know I"m overlooking something here but these questions/thoughts came to me reading this thread and trying to follow the various pieces of advice.

Help a fellow out.

Edited by gcbryan, 26 January 2006 - 09:41 AM.

[ScubaDadMiami]

Mention was made somewhere in the thread about checking the shift full to empty for an individual tank. I just want to point out in case it's not obvious that the shift itself doesn't depend on the tank but rather how much gas the tank holds. Air weighs the same whether it's in an aluminum or a steel tank. The shift will be about 6 lbs for 80 cu ft. whether the tank is aluminum or steel.

Correct. However, that could result in becoming neutral, or somewhat negative, with steel tanks, compared to positive as much as 8 pounds with double aluminums.

I have a question regarding those talking about making sure one can swim a steel tank up after a BC failure and it being easier with an aluminum tank. Unless you are talking about ditching your weight belt it should be the same shouldn't it? And if you are talking about ditching your weight belt then swimming up would be the least of your problems. I'm confused here. Steel tanks take more weight off of your weight belt but it goes right to your back. The weight is the same unless you are talking about ditching the weight belt. Help me out here.

Assuming an ocean dive, if you are diving double 120 steels, you are over 21 pounds negative when first jumping in with full tanks. At the end of the dive, you are neutral. So, you will need less weight than with aluminum tanks to offset your positive buoyancy of the rest of your equipment.

With aluminum 80s, you are at about negative 12 or so at the start of the dive. You should be neutral at the end. You will need about 8 pounds or so of lead to offset the tanks' positive buoyancy at the end of the dive. Add to that to compensate for your remaining equipment.

Of course, both of these scenarios are based on empty tanks. So, you really should be a little more negative than this at the end of the dive if you have gas left in your tanks. However, the point is, if you have a wing and drysuit failure with double steels at the beginning of a dive, there is quite a bit of difference in the effort required to swim these up compared to aluminum 80s. Even if you ditch weight, you will still be pretty negative in the steels when compared to the aluminums.

Also, there was something mentioned about one's drysuit flooding and having to take it off to avoid sinking down to the bottom. Remember water is neutrally buoyant. If you completely flood your drysuit you do not take it off.

You are right. However, since the thermals you are wearing under the suit have some positive buoyancy, that will be at least partially lost once flooded. Then, you could become extremely negative. Also, don't forget that, when you get back to the surface, you might require a crane to get out of the water and back onto the boat.

[intotheblue]

thanks to trace and the ginnie springs clinic, i am working on that setup myself.... i really like the low pressure 72 steel tanks. at a 10percent overfill they hold 77 cubic feet. they are much less BULKY and more comfortable than the al80 and hold about the same gas at much less pressure (2250 +10percent). because you use so little air, i cant imagine you needing anything with more capacity. when i asked trace about why the market promotes aluminum tanks, he gave me several answers, but i think the biggest factor is cost. there are also the newer high pressure steel tanks...i have no experience with them and would love some feedback.
my advice would be to go rent a set of al63 and a set of steel 72 and al80s and experiment with al and steel backplates to get your weight right. the steel tanks shouldnt be as much of a problem in saltwater. ultimatly, the biggest problem with steel tanks seem to be, " what can you swim up from depth if your bc fails"
i really dont like aluminum tanks, and after trying on a set of double al80 tanks i definatly would prefer to go with steel. just remember what is right for someone else might not be right for you, and i was really lost on this subject till i started asking trace and norm questions at ginnie springs.

Well, I guess I had to read the entire thread after all. Is someone making "new" stl 72's??? Stl 72's for the longest time that were rated at 2250 lbs (plus a 10% overfill) and were actually about 64.7(or something close to that) cu ft cylinders. They were only 71.2 cu ft. when overfilled. They were called 72 cu ft. Anyone have different data than this??? Most other "low pressure" steel cylinders I am familiar with are rated to 2460 lbs (U.S.) and can legally receive a 10 % overfill if the last test indicated it was ok to do so. Of course, Europe and cave divers use these cyliniders beyond that, but you should make sure you have a thorough understanding of the cylinder and its condition and applicability for such overfilling (still violates DOT regs).

Most of the steel 72's around are older and many will not pass hydro... and I'm not sure if they actually fail or if testing facilities are going out of their way to remove them from service. I have had several that looked great (in and out), never had significant overfills, and were "failed" by local testers. Nobody I have talked with in the cave community would think of "cave-filling" a stl. 72. Most are used as cave deco cyls. that are left clipped off at 20 ft in the cave where their negative buoyancy holds them in place on the floor somewhere... and they are usually only filled with about 2200 psi of O2.

Now... later we may have to re-visit the issue of weighting in fresh vs. salt water... if someone else doesn't clarify that. I'm out of time for now.

Happy diving...