What size of steel tank for beginner doubles?

[1_T_Submariner]

I too am interested in this topic. Not to Hijack just a question.

Would you want to try to size your tanks to be close to your partners taking into account gas consumption etc...?

I am 5' 10' and my 3500 psi steel 120 is just a little to tall for me. Would this make the same tanks doubled worse or better?

 

[dannobee]

Either way there is little or no reason to buy an LP tank when you compare dimensions, bouyancy traits and capacities at various pressures as the 3442 psi tanks offer more gas in the same size/weight package.

Sure there is. If you frequently dive off of boats with compressors, or your shop doesn't pump to high pressures, you'll be left with far less gas than the rated pressure, especially if their fills are hot.

I don't know where you're from, but here in sunny California, the dive boats rarely pump over 3000psi. With the LP tanks you can tell them to pump them to 3000 and when they cool back down, they'll be just right.

If you're diving with double HP80's, then get a short, hot fill, you'll have less gas than you would with a big single tank.

 

[Walter]

I'd match my tank size to the amount of air I need for the dives I'm planning. Lynn makes an excellent point with regard to double 72s vs a single 130, but doubles are easier to dive, they don't roll you over as easily, the weight is more evenly balanced across your back, so there's no need to balance a heavy tank on the center of your back.

 

[Gilldiver]

I put this together a while ago, but I feel it is still current. However, I would add that an old set of steel 72s from the 1970s make for a nice first set for open water wreck diving with little if any penetration.

In the garage is a set of these 72s, 2 sets of 80s, a set of 100s, 3 sets of 120s and a bunch of 40s, and 80s for stages and a single steel 125. They all have their uses but I find that the 72s, the single 125 and one 40 are the most used for my normal/common diving between 60 and 130' on open or flattened wrecks up here in the Northeast.

Pete Johnson

After 28 years of diving, every time I get asked about doubles I ask back "what do you want to do?" Doubles let you do two things that a single can't- stay longer at shallower depths and go deeper. Both of these bring on DECO and/or gas planing problems very quickly. If you are not prepared for DECO and gas plans, then stay with the singles and NDL diving. If you want some extra gas, a small 20/30/40 bottles as a pony or stage work well.

Now what do you do with the extra gas - most divers will use the gas for exploration of some type be it wrecks, caves, reefs, or photos. At this point the diving has become a tool that lets you do that other thing.

For anyone who wants to go further and get into doubles. I always recommend starting with the old standard aluminum 80's. Why?

Less cost - for your first set of doubles picking up 2 80's used can be done for less then $160 (sometimes much less say $50 each), add a manifold (new $200/used $100) bands (new $65-$100/used $50). Total cost $300-$350. Or a little over what you might pay for a single steel tank. A new set of tanks, manifold and bands will run at least $750 and can get up to a grand. Also, as you travel around the world you will most likely only find aluminum 80's. So if you plan to travel, get used to using them.

Weight - I think you can figure this part out. Steels on land suck and for boats, it is not getting off that you worry about (gravity will see to that) it is getting back on. A fully rigged set of 120 or 130's will be a bit*h to control on a marginal day and bucking ladder.

Now go diving - a lot.

Is this what you really want to do? Do you want to put the time and money into it? Will you get bored in 2 years? The sad fact of it is that many, if not most, of the people who post on this board will drop out of the sport in 3 years or less.

OK, if you made the jump to deep/long diving and need more gas then the 80's. Break up the set, the 80's are now called stage bottles, and get the steel tanks you need to do that thing you want to do. The manifold can be reused and maybe the bands.

Now you have a large set of steel tanks, 2 80 stages, and most likely a 20-40 foot small bottle. You now have the tanks to jump 200-250+ feet or go a long way back into a cave- if you want to.

Many will question the 80's because of trim but we can work you through that problem quickly.

Now go diving, - A lot. Play with your rig, adjust the BC/back plate and compensation weights till you get what works for you There is no substitute for experience.

As for your regs, the posts above go through the standard way of rigging them. I might also suggest that you get Y or H valves on your singles and a dedicated BC for the doubles. That way your regs and back plate transfer between the doubles and singles with no changes in configurations.

Finally have fun.

Pete Johnson

 

[Grey_Wulff]

I'm also in the process of putting together my first set of doubles. We're starting tech training shortly and both courses we're considering require a minimum 200cf setup. Thus, I'll be doubling my HP100's rather than doubling either set of my 80's.

Grey_Wulff

 

[WD8CDH]

Quote:
Originally Posted by DA Aquamaster
Either way there is little or no reason to buy an LP tank when you compare
dimensions, bouyancy traits and capacities at various pressures as the 3442 psi
tanks offer more gas in the same size/weight package.


Sure there is. If you frequently dive off of boats with compressors, or your shop doesn't pump to high pressures, you'll be left with far less gas than the rated pressure, especially if their fills are hot.

I don't know where you're from, but here in sunny California, the dive boats rarely pump over 3000psi. With the LP tanks you can tell them to pump them to 3000 and when they cool back down, they'll be just right.

If you're diving with double HP80's, then get a short, hot fill, you'll have less gas than you would with a big single tank.

DA is correct, The HP tanks have almost the same weight/buoyancy traits as the equivilent LP tanks with the same fills. For example, the HP Steel X7-100 holds 80 cu ft at 2640psi. The LP 85 holds 82.7 cu ft at the same pressure but weighs 1 pound MORE, is .7" LONGER and requires 2.5 pounds MORE weight on the weight belt to achieve neutral buoyancy.

Double HP 80s at 2640psi would require a LP-120 to hold almost the same air. But the single 120 would require a little over 7 1/2 pounds MORE weight on the belt, would be almost 10 inches longer and would hold 8 cu ft LESS air.

Also remember a fill into a LP tank will be just as hot as a fill into a HP tank at the same pressure.

 

[DeepSeaExplorer]

I put this together a while ago, but I feel it is still current. However, I would add that an old set of steel 72s from the 1970s make for a nice first set for open water wreck diving with little if any penetration.

In the garage is a set of these 72s, 2 sets of 80s, a set of 100s, 3 sets of 120s and a bunch of 40s, and 80s for stages and a single steel 125. They all have their uses but I find that the 72s, the single 125 and one 40 are the most used for my normal/common diving between 60 and 130' on open or flattened wrecks up here in the Northeast.

Pete Johnson

After 28 years of diving, every time I get asked about doubles I ask back "what do you want to do?" Doubles let you do two things that a single can't- stay longer at shallower depths and go deeper. Both of these bring on DECO and/or gas planing problems very quickly. If you are not prepared for DECO and gas plans, then stay with the singles and NDL diving. If you want some extra gas, a small 20/30/40 bottles as a pony or stage work well.

Now what do you do with the extra gas - most divers will use the gas for exploration of some type be it wrecks, caves, reefs, or photos. At this point the diving has become a tool that lets you do that other thing.

For anyone who wants to go further and get into doubles. I always recommend starting with the old standard aluminum 80's. Why?

Less cost - for your first set of doubles picking up 2 80's used can be done for less then $160 (sometimes much less say $50 each), add a manifold (new $200/used $100) bands (new $65-$100/used $50). Total cost $300-$350. Or a little over what you might pay for a single steel tank. A new set of tanks, manifold and bands will run at least $750 and can get up to a grand. Also, as you travel around the world you will most likely only find aluminum 80's. So if you plan to travel, get used to using them.

Weight - I think you can figure this part out. Steels on land suck and for boats, it is not getting off that you worry about (gravity will see to that) it is getting back on. A fully rigged set of 120 or 130's will be a bit*h to control on a marginal day and bucking ladder.

Now go diving - a lot.

Is this what you really want to do? Do you want to put the time and money into it? Will you get bored in 2 years? The sad fact of it is that many, if not most, of the people who post on this board will drop out of the sport in 3 years or less.

OK, if you made the jump to deep/long diving and need more gas then the 80's. Break up the set, the 80's are now called stage bottles, and get the steel tanks you need to do that thing you want to do. The manifold can be reused and maybe the bands.

Now you have a large set of steel tanks, 2 80 stages, and most likely a 20-40 foot small bottle. You now have the tanks to jump 200-250+ feet or go a long way back into a cave- if you want to.

Many will question the 80's because of trim but we can work you through that problem quickly.

Now go diving, - A lot. Play with your rig, adjust the BC/back plate and compensation weights till you get what works for you There is no substitute for experience.

As for your regs, the posts above go through the standard way of rigging them. I might also suggest that you get Y or H valves on your singles and a dedicated BC for the doubles. That way your regs and back plate transfer between the doubles and singles with no changes in configurations.

Finally have fun.

Pete Johnson

Nice post...

The number one factor for selecting doubles is the intended use and the required gas volume. That's why most divers end up with several sets, because they do more than one type of diving.

The exposure suit isn't really an issue because you can properly setup with either, both AL and steel tanks can be dived wet or dry.

I always recommend starting with AL 80s for just the reasons you mention. They make the best starter set and have the best all around usage. The only exception would be if you're going straight to cave diving. That would be the only case where I would recommend starting with steel tanks.

 

[dannobee]

Double HP 80s at 2640psi would require a LP-120 to hold almost the same air. But the single 120 would require a little over 7 1/2 pounds MORE weight on the belt, would be almost 10 inches longer and would hold 8 cu ft LESS air.

If you're splitting hairs, the two HP80's would weigh 30 lbs each-not counting the bands and manifolds. The single LP120 would weigh 45 lbs. And the 3442psi tanks would hold 122 cu ft-roughly the same as the LP120.

But I do see what you're saying.

 

[DA Aquamaster]

DA is correct, The HP tanks have almost the same weight/buoyancy traits as the equivilent LP tanks with the same fills. For example, the HP Steel X7-100 holds 80 cu ft at 2640psi. The LP 85 holds 82.7 cu ft at the same pressure but weighs 1 pound MORE, is .7" LONGER and requires 2.5 pounds MORE weight on the weight belt to achieve neutral buoyancy.

Double HP 80s at 2640psi would require a LP-120 to hold almost the same air. But the single 120 would require a little over 7 1/2 pounds MORE weight on the belt, would be almost 10 inches longer and would hold 8 cu ft LESS air.

Thanks for underscoring the point with some numbers.

Divers often look primarily at volume when selecting a tank but fail to look and compare the whole package and miss the point that a 3442 psi tank of a given size holds a lot more gas at its service pressure than a LP tank of similar size and weight and further miss the fact that both tanks hold very close to the same amount of gas when both are filled to the LP tank's much lower service pressure.

So in short, short fills on a 3442 psi tank are not an issue as you are going to get a lot more gas in your 3442 psi tank (of similar size and weight compared to the LP tank you may have bought instead) at 3000 psi than you would have gotten with a full fill in a low pressure 2400 psi tank at its 10% overfill pressure of 2640 psi.

And 5 years from now, the 3442 psi tank can still be filled to 3442 psi while the LP tank will be limited to only 2400 psi unless you can find a test facility that will (+) rate it again for the 10% overfill.

With the widespread availability and sound service record of 3442 psi tanks, LP tank really do not make nearly as much sense anymore as they used to.

 

[PerroneFord]

With the widespread availability and sound service record of 3442 psi tanks, LP tank really do not make nearly as much sense anymore as they used to.

Depends very much on where you live.