Steel vs Aluminum in cold water ?

[JohnAC]

Hi all,

I am in the process of switching from a stab jacket bc to a Hog rig. I dive primarily in the Socal area and always wear 7mm suit. I purchased a steel back plate and am wondering about steel vs aluminum tank. I usually dive a barrowed NB aluminum 80, but am considering steel 100.

I have read threads on bouyancy issues with steel tanks in OOA situations, but I am not interested in tech or doubles, just a little more air & less weight on the belt as a rec diver.

Anyone dive 7mm wetsuit, single steel tank, bp/w, Socal area? How much lead are you carrying?

I weigh 186lbs. In my jacket rig I carry 6lbs on AL tank & 22lbs on a belt. I look forward to taking some of that off in the new Hog rig.

Thanks for your comments!

 

[Thalassamania]

There are several issues, the most import, in my mind, is that once you use a heavy backplate (or a weight integrated BC) you can no longer remove your tank without being a candidate for a Trident Missile trip to the surface. I often dive aluminum and steel tanks with a 7mm wetsuit. I wear all my lead on my waist and use a plastic backback.

 

[Charlie99]

Just as important, if not more important than the change to a steel tank, is the effect of going to a steel backplate, and a single tank adaptor if you add that.

It's not like it's rocket science to figure out the approximate weighting changes.

You have a NB AL80 -- which is close to neutral when empty. Look at the empty buoyancy spec for whatever tank you are considering. It will probably be a few pounds negative when empty --- that's how many pounds of lead you will be taking off of your belt for the tank change.
http://www.huronscuba.com/equipment/scubaCylinderSpecification.html

Your backplate will probably be another 6 pounds negative. Then you may or may not have a few pounds negative buoyancy in a single tank adapator.

Total it all up together and find out how much lead you'll shed. It will still be less than 22 pounds, and you will probably still have more lead on your belt than the air in the tank weighs -- so if your wing won't hold air on the surface at the beginning of a dive, at the worst case you can drop lead to get positive.

 

[JohnAC]

There are several issues, the most import, in my mind, is that once you use a heavy backplate (or a weight integrated BC) you can no longer remove your tank without being a candidate for a Trident Missile trip to the surface. I often dive aluminum and steel tanks with a 7mm wetsuit. I wear all my lead on my waist and use a plastic backback.

What is your trim like with all that weight on the waist?

Obviously you are extremely experienced!

Have you ever had to ditch your rig?

 

[Thalassamania]

What is your trim like with all that weight on the waist?

Obviously you are extremely experienced!

Have you ever had to ditch your rig?

Trim is just fine, and yes I have had to remove my rig.

 

[Eris Lucan7*]

It is unimportant what you use aslong your tanks have a proof.

On a stop with a traedership at the old German Warmarineoutpost at the Kronprinzesin

Marta Ilands in the antartiks, we had used a the Sationary warmaircompressor and

the tank as emergncy Option,thats the best in cold water.

E.L.7*

 

[Luis H]

There are several issues, the most import, in my mind, is that once you use a heavy backplate (or a weight integrated BC) you can no longer remove your tank without being a candidate for a Trident Missile trip to the surface. I often dive aluminum and steel tanks with a 7mm wetsuit. I wear all my lead on my waist and use a plastic backback.

I totally agree. I don't like this tendency to have a heavy rig and a buoyant diver.
Always believe in being close to independently neutral from my rig.

What is your trim like with all that weight on the waist?

Obviously you are extremely experienced!

Have you ever had to ditch your rig?

I adjust my trim by moving my weight belt up or down just a bit (with a 20+ Lb weight belt it doesn’t take much moving to change trim). Within reason, I can adjust or change my trim while swimming.

I have also had to remove my rig underwater several times, to untangle rig, check for leaks and inspect rig, etc. etc.


I used to swap rigs underwater with my buddy to test/ try each others regulators (back in the 70’s, I worked in a dive shop and had access to many regulators to try). We were both equally neutral.

 

[Thalassamania]

I totally agree. I don't like this tendency to have a heavy rig and a buoyant diver.
Always believe in being close to independently neutral from my rig.

I adjust my trim by moving my weight belt up or down just a bit (with a 20+ Lb weight belt it doesn’t take much moving to change trim). Within reason, I can adjust or change my trim while swimming.

I have also had to remove my rig underwater several times, to untangle rig, check for leaks and inspect rig, etc. etc.


I used to swap rigs underwater with my buddy to test/ try each others regulators (back in the 70’s, I worked in a dive shop and had access to many regulators to try). We were both equally neutral.

Great minds think alike, on the other hand ... so do ours.

 

[John_B]

I totally agree. I don't like this tendency to have a heavy rig and a buoyant diver.

Given that your initial gas weight is maybe 6 lbs for an AL80, at the start of a dive do you plan for the rig to be overweighted or the diver?

John

 

[nereas]

The problem lies in the thick wetsuit. Until you fix that, you cannot afford a lot of non-ditchable weight. A steel tank is non-ditchable weight. Attached to a steel backplate is even more of the same.

On a shallow dive there might not be any problems, as long as there was an ocean floor underneath you that you could crawl around on, to arrest your descent. On a deep dive to a pinnacle, this all changes. If you miss the pinnacle, you are then S-O-L.

The general rule is this:

wetsuit + aluminum tanks

drysuit + steel tanks

steel backplate + aluminum tanks + wetsuit

steel backplate + steel tanks + drysuit

Therefore the suggestion with a thick wetsuit like a 7mm would be with an aluminum tank. You can add a steel backplate if you want, but the rest of your weight should be ditchable. And no more steel than that, until you get a drysuit, which does not shrink at depth and then suddenly re-expand on ascent, like a wetsuit does.