Steel tanks dangerous?

[fisherdvm]

So my understanding is ... as one get larger tanks in singles ... one is exposed to the dilemma of not being able to swim up if the tank is too negative at the beginning of the dive. An advantage of aluminum tank is shifting that weight to the weight belt.

 

[boulderjohn]

So my understanding is ... as one get larger tanks in singles ... one is exposed to the dilemma of not being able to swim up if the tank is too negative at the beginning of the dive. An advantage of aluminum tank is shifting that weight to the weight belt.

Correct.

To repeat what I said earlier, your total package as a diver--you, your thermal protection, your weights, your gear, your tanks--is neutrally buoyant when its total weight equals the weight of that volume of water. If 2 tanks are about the same size and one weighs less than the other, then you need to add weight somewhere else to balance that out.

As I also indicated above, a key reason many people like steel tanks is gas volume. The steel 120 mentioned above has about 50% more gas in it than an AL 80.

 

[Soloist]

So my understanding is ... as one get larger tanks in singles ... one is exposed to the dilemma of not being able to swim up if the tank is too negative at the beginning of the dive.

You may understand, but I am throughly confused by your statement.

 

[DanielRJones]

So my understanding is ... as one get larger tanks in singles ... one is exposed to the dilemma of not being able to swim up if the tank is too negative at the beginning of the dive. An advantage of aluminum tank is shifting that weight to the weight belt.

aluminium or steel you are only negative at the start of the dive the weight of air in your tank that you will use in your dive so you will be about 6lb negative on a 100cf tank that does not matter if it is steel or aluminium. You will also be negative the compression of your thermal protection. the thicker your protection the more buoyancy it will loose as it compresses.

aluminium tanks are heavier on the land than steel tanks but in the water due to them being bigger are lighter by about 4lb when comparing similar tanks.

this means you will have to wear an additional 4lb of weight if you are diving an aluminium tank. Yes this means you have more weight on your belt that if you ditch it may help you do an uncontrolled ascent to the surface with a 5mm wetsuit i have to still wear 12lb of weight with a 12l steel tank so i still have plenty to dump and having tested myself at 27m in a 7mm wetsuit i can wind myself in on my DSMB.

 

[Remy B.]

Honestly I think you are overthinking it and you have not get your buoyancy under the arm.

a BCD failure is most cases on the inflator, which leave you to the oral inflator, but if your inflator is bad you will spotted on your surface check, if you have a leaking BCD it is normally nothing mayor, if it is a mayor leak that means that you are not taking care of your equipment.

Even if it is a mayor leak, at the end it is a plastic sac that will trap air on the opposite side of the leak, meaning that you need to shift your position so that air get trapped.

It seems that your are patching some problems with something that is not likely to happen and that if it happen it can be dealt with,

 

[fisherdvm]

a BCD failure is most cases on the inflator, which leave you to the oral inflator, but if your inflator is bad you will spotted on your surface check, if you have a leaking BCD it is normally nothing mayor, if it is a mayor leak that means that you are not taking care of your equipment.

It seems that your are patching some problems with something that is not likely to happen and that if it happen it can be dealt with,

 

[fisherdvm]

I think most failures are at the attachment of the inflator hose to the bc. Which is usually one of the highest point in the profile of most divers. It has happened to me once. But thanks for pointing out the options. In the water, one can not decipher where the leak is. Hindsight is 20/20z.

 

[Magnus Lundstedt]

The real problem is not the difference between Alu or steel tanks. Other than you can have more ditchable weight with Alu tanks.

The problem is thick wetsuits with big swing in boyancy.

To solv that problem you can use Alu tanks and get more weight in the belt, but with thick wetsuits you get big boyancy swing and if you ditch weight in 30 meters you are going to get a fast ride to the surface when you come up a bit.

My take on the problem is that you can either get a dry suit that dont swing as much, or you can get yourself some redundant lift, DSMB/Liftbag can help.

 

[Colliam7]

So my understanding is ... as one get larger tanks in singles ... one is exposed to the dilemma of not being able to swim up if the tank is too negative at the beginning of the dive. An advantage of aluminum tank is shifting that weight to the weight belt.

Yes.

But, isn't the issue more complicated than just steel cylinders vs aluminum?

1. If you use a steel cylinder, vs aluminum, you are probably using a cylinder that is more negative at the beginning AND end of the dive. So, you would adjust your weighting for the cylinder.

2. The difference in your buoyancy at the beginning and end of a dive is the weight of the air used. The change in buoyancy is shown below for a series of cylinders:
a. 80 cf (AL or steel) 6.5lb
b. 100 cf (AL or steel) 8.1 lb
c. 120 cf (steel) 9.7 lbs
d. 130 cf (steel) 10.5 lbs

So, the difference between the beginning and end of a dive, even for a HP 130 is (only) ~10.5 lbs. Yes, as the size of the tank (irrespective of metal) increases, the added weight at the beginning of the dive is greater.

3. The admonition against diving wet suits and steel cylinders is most often voiced with regard to double steel cylinders. The double steels may be so negatively buoyant that the diver requires no added weight and, in fact, is still negatively buoyant with empty cylinders at the end of a dive. If that was the case, AND the diver had an additional 16 lbs (e.g. diving double HP 100s) to swim up at the beginning of a dive, it might be difficult.

4. There is nothing that can be done to change the loss of buoyancy associated with the compression of a wetsuit, other than not dive as deep, or wear thinner suits, where the change in buoyancy between the surface and depth (e.g. 100 ft) is less.

5. Something can be done with a drysuit - add air, presuming that a buoyancy failure which would create a problem was limited to the diver's primary buoyancy source.

I think the thread would be better titled, 'Should I always dive a balanced rig?". I see no evidence to support 'steel tanks dangerous?' or even, 'Large tanks dangerous?'.

 

[Soloist]

I think the thread would be better titled, 'Should I always dive a balanced rig?". I see no evidence to support 'steel tanks dangerous?' or even, 'Large tanks dangerous?'.

Exactly! There have been other threads about balanced rigs, why not post the question there? This is the problem with sensationalized titles about “virtual diving” scenarios. Pose the question properly and intelligently if you are actually interested in a productive discussion. It is irresponsible to purposely scare people in the “Basic Scuba Discussions” forum with such nonsense and is a disservice to new divers. The moderators should change the thread title to prevent unnecessary confusion.