Tank size for new divers

[Scuba_Vixen]

Well, some people have lungs the size of coffee cans but the guy asking this question probably has twin gallon jugs. Given this, decreasing the air consumption rate is problematical. Size, weight and muscle mass make it so. Other than metabolism, air consumption is partly a head game. Free diving builds endurance and self control and is a more rigorous training method than any kind of indoctrination in a class setting. Some unusually nervous people seem to improve with SCUBA experience, especially if they have moderate height and weight. One way to test this is to start them with a double hose regulator then move on to the single hose when they stop complaining of air 'starvation'.

Your theory that anyone that's big, and therefore has big lungs is a "natural born Hoover" just is Not supported in reality. There are many big guys in diving with working sac rates of .6cfm or better and resting sac's of .5 or better. There is a greater number that's slightly higher, but still close. The ONE thing they all have in common is: They were Much Worse when they first started.

You're suggesting a new diver use a lame excuse (his size), to not even try to significantly improve. I think most of us here are of the opinion that you need to rethink your position a bit.

If you fail to get better as you go on, .... You're actually then, Getting Worse .....

Darlene

 

[pescador775]

You ignored two practical suggestions which I made for reducing air consumption. Also, I repeat that it is more difficult for really big men to lower peak air consumption. Even if 'SAC' is lowered while resting these men respond differently to stress and exercise. In a foot race, or while struggling underwater, regardless of SAC (LOL, acronyms galore) a big man will use more air than a small one or especially, a woman. It is simple physics. Given this, it is wrong to instruct a big man that he will eventually be able to use a small tank when it is obvious that he needs more air. To make it simpler to understand, a reduced air consumption level while sitting on thel bottom of a pool is often achievable through accomodation and relaxation. However, increase in air consumption will be proportionately greater when struggling with a bushel of oysters, restrictive dive dress, cold water and current. There are exceptions which some might be tempted to 'jump on'. Let me beat the learned doctors to it. As I have said, it is possible through mind control and relaxation techniques for certain determined individuals to actually lower metabolic rate. These people are about as common as Olympic athletes and are generally found in the small population of freedivers. Divers who repeat the same clear water dive learn to relax and use less air. The first time he dives a cold bay while trying to hook an anchor into a wreck and can't figure in which hand to hold the light becauses visibility is 3 feet, then work rate and air consumption will rise. Later, it becomes apparent that the small tank that he recently bought is running low and his buddy is wondering why the dive is being aborted. (Grrrrrrr)

You're suggesting a new diver use a lame excuse (his size), to not even try to significantly improve. I think most of us here are of the opinion that you need to rethink your position a bit.

 

[jonnythan]

There's a difference between a larger tank and one that holds twice as much as a "normal" tank. 100 cf is fine, 120 cf is ok but still a bit bit.. 150 cf is gigantic. You'll literally never use that much gas, and if you do you will probably find yourself deep into deco.

Unless you plan on spending over three hours at 30 feet (which you could, even with a bad SAC). That much gas for a newbie is unnecessary at best and possibly dangerous.

 

[pescador775]

Yeah, I agree. The 149 is good for one deco dive with a 10-15 minute stop plus some air left over for an anchor pull. This is what the twin 72 rig was used for and I would expect the same profile with the single tank. However, I do note that the deco tables were more liberal in those days. A 120 should be more than adequate for most reef dives to 60 feet and a bounce to 130 feet.

There's a difference between a larger tank and one that holds twice as much as a "normal" tank. 100 cf is fine, 120 cf is ok but still a bit bit.. 150 cf is gigantic. You'll literally never use that much gas, and if you do you will probably find yourself deep into deco.

Unless you plan on spending over three hours at 30 feet (which you could, even with a bad SAC). That much gas for a newbie is unnecessary at best and possibly dangerous.

 

[Scuba_Vixen]

Yeah, I agree. The 149 is good for one deco dive with a 10-15 minute stop plus some air left over for an anchor pull. This is what the twin 72 rig was used for and I would expect the same profile with the single tank. However, I do note that the deco tables were more liberal in those days. A 120 should be more than adequate for most reef dives to 60 feet and a bounce to 130 feet.

WTF are you thinking ....... Deco dive planning with a single tank !!! Now you're putting the noose in the end of that rope. You guys must really do things differently where you are.

Darlene

 

[nyresq]

WTF are you thinking ....... Deco dive planning with a single tank !!! Now you're putting the noose in the end of that rope. You guys must really do things differently where you are.

Darlene

If you use an H-valve you have the same redundancy (sp?) as diving doubles with the exception of a tank o-ring extrusion, which is extremely rare to begin with.
There are lots of people who use H-valves or Y-valves for deep or penetration dives with full deco procedures. I don't think diving a single tank with an H-valve is having a death wish. I've been diving for 14 years and have never had a tank ring blow, nor have I ever seen one go, and know onlyone person who said they had one go.... and that was on a valve that was hand tight with rust around the neck.
Proper deco uses a deco mix in addition to your back gas. Doing deco with out using a seperate high O2 deco mix (50 or 100%) in a sling bottle is like driving a ford escort at a racing school.
If you've taken the class and can use a high O2 for deco, why wouldn't you???
With the big tanks that are available these days you get more gas then the doubles people were diving 10 years ago...

 

[pescador775]

Shush, that cuts into tank sales.

If you use an H-valve you have the same redundancy (sp?) as diving doubles with the exception of a tank o-ring extrusion, which is extremely rare to begin with.
There are lots of people who use H-valves or Y-valves for deep or penetration dives with full deco procedures. I don't think diving a single tank with an H-valve is having a death wish.

 

[nyresq]

Shush, that cuts into tank sales.

well they still have to buy sling bottles don't they!!!! :lol2:

 

[Scuba_Vixen]

In the post that I called to task, there was never any mention, not even a hint, of anything other than use of the single tank with the usual recreational K valve and reg setup.

I have no issues with H or Y valve setups on large capacity singles for those *properly trained* to make use of them. That configuration for light deco diving with appropriate deco gas is not unusual. The issue is that one needs to be *Properly trained and experienced* before diving at that level. By the time most anyone has completed adv. nitrox / deco proced. ... they likely have at least 100 to 200 dives under their belt and in that time, have gotten their sac rate well under control.

The initial post was from a gas guzzling new diver who wanted support for buying the biggest tank commonly available as a band aid approach to his novice level breathing skills. That just encourages bad habits, making them even harder to break later, when the realization that it's a bad habit sinks in.

I think the only responsible response is to warn him off of that approach, and towards something more like: experience, lots of skills work, and maybe an hp100.

Darlene

 

[Wreck]

Take this as advice, not as a slam, but as a new diver, you dont need a cylinder that holds 149 cu ft of gas. Rethink your choice of cylinder. Your logic is sound, but the choice of cylinder is wrong. That sam logic will work with a E7-100, which is much lighter, more manageable, and more along the lines of what you need for the types of dives you will be doing in the immediate future. Dont get ahead of yourself.

I'm still a brand-new diver, but decided to buy my own tanks early on. I did some math and found out I would break even between costs of rentals and owning my own tanks after 75 dives, excluding the annual visual. I plan to make 50 this summer alone. Big tanks are are a big investment, and I did not want to end up not using the ones I bought initially in favor of something more suitable for later types of diving.

The thought of having a bit more bottom time (within NDL) was one thought that went through my mind as I eyed the pair of PST 119s I have now. However, I learned that's not really a big issue (as others have explained) through my own experience. The thought of having a bit of extra air in case of anything totally unexpected (stress or emergency) happening and that I could burn air with reckless oblivion and still have more left over than my experienced buddy with an 80 was a bonus that made me more relaxed about dealing with any unforeseen risks. Those aren't really good reasons to get something big though.

My main reason to go with bigger tanks was that I fully intend to move into deep diving (adv trimix) within a couple years. Tech guys here that do that type of diving are using these same tanks configured as doubles. So I considered these larger tanks an investment into my future that I could also appreciate using NOW. This reasoning may not apply to the original poster though.

I know these are wider than the standard 80, but I don't really notice much additional aquadynamic drag in comparison..... yet.

Someone pointed out that having more capacity is an invitation to violating NDL. It's a valid argument, but I doubt any of us were taught to use remaining air capacity as the only guage for NDL. I think most divers understand this so it's practically a moot point to me except for those who are tempting Darwinism to strike.