How to choose a tank

[mike_s]

That is not always true. My body is negatively buoyant. In a 3mm wetsuit, I am neutral. In a 7mm wetsuit, I am positive. I think most people are something close to neutrally buoyant.

You are correct. I should have said most people bodies are positive buoyant. (they float).

Not everyone does.


I guess what I was trying to point out that not ever shoe fits ever foot. it shouldn't be assumed that wetsuit divers should never use steel tanks. People are different and so are tanks.

 

[dschonbrun]

I'm a wetsuit diver, and I'm considering using a steel tank with my BCD. It would mean I could carry less weight on my belt.

 

[ekewaka]

I guess what I was trying to point out that not ever shoe fits ever foot. it shouldn't be assumed that wetsuit divers should never use steel tanks. People are different and so are tanks.

That is precisely my point. There are some divers who can use steel tanks with a wetsuit, and there are some who should never use steel tanks with a wetsuit. It should not be assumed that steel tanks are always better. They are better for some divers and not for others.

 

[nereas]

I'm a wetsuit diver, and I'm considering using a steel tank with my BCD. It would mean I could carry less weight on my belt.

Then as I said above, if you are seriously considering wearing steel tanks with a wetsuit, then you should also wear a double-bladder wing for redundancy, since you are likely to remain "negatively buoyant" (i.e., un-buoyant) during your entire dive, even with your tank almost empty.

Oxycheq offers these kind of wings, and you can attach one to your BPW or your B/C, whichever you have. You surely should not be wearing a jacket style BCD with steel tanks and a wetsuit, however, since there is no redundancy in that.

 

[FredT]

Dry divers will generally do better with steel tanks as it'lll reduce their overall weight requirement when on deck, or getting back on deck from a dive.

Wetsuited or bare skin divers will require more thought. I prefer steels, but I don't dive thick wetsuits any more. Thick foam suits and deep dives may require aluminum tanks for optimum buoyancy.

As a rule with my inherent buoyancy characteristics though if a magnet won't stick to the tank it's off my "buy it" list. Consider a steel tank a "lifetime" investment if properly cared for. A 6351 Al bottle is scrap now most places since many shops chose to ignore the DOT requirement for eddy current testing and have a blanket refusal to fill them. A 6061 Al bottle is good or 10 to 15 years normal seawater use at best unless exceptionally well maintained and filled ONLY at a "pristine" air source. I still haven't found a consistantly "pristine" air source. I'm still diving some steel bottles older than I am. Considering I've been diving almost 40 years that says a lot for the life expectancy of the steelies.

My simple buoyancy requirement is to always be able to swim up my rig even if the BC looses all lift. Diving appropriately sized single steels FOR ME this isn't a problem as I float pretty well all by myself. Diving doubled high capacity steels requires either a dry suit or lift bag to lift the tanks if the wing gets eaten by an oil rig during a nantucket sleighride. Oil rigs off the MS and LA coast are effectivly bottomless, in that either the water just gets thicker or the depth is deeper than a diver can go open circuit and make it back to the surface still breathing.

FT

 

[rainman_02]

Let's see...

A single AL80 has a buoyancy swing from -1.4lb to +4.4lb. I wore somewhere around 20lbs of lead with a 7+mm suit (Polar Tri-density 6/7/9) and a 6lb backplate. At the end of the dive, I am neutrally buoyant at 10 feet with 500psi in my tank and no air in my BC. That means I am 5lbs negative at the start of the dive (plus whatever suit compression).

A single X7-100 has a buoyancy swing from -10lb to -2.5lb. I wore about 14lbs of lead with the same suit and plate. Again, I am neutral at the end of the dive...so I am 7.5lbs negative at the start (plus suit compression).



That is a WHOPPING 2.5lbs difference. Think I can swim that up? You bet. Even considering a total BC failure, I can swim against it and get to the surface where I can ditch my weight belt. Then I'll be really positive.


References:
Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan
Scuba Tanks, Aluminum 80's, Pony Bottles, Spare Air Bottles, Steel Cylinders

 

[rainman_02]

The point of that little exercise was simply: you do not need redundant buoyancy for the weight you can swim up. It is a concept called a "balanced" kit.

 

[Stu S.]

Most of you have the chart already. It should help the decision-making process. I take off four pounds of lead to go from AL to a Faber FX-100. That still leaves 12 to ditch in salt water. My pal has Worthington 100's and takes off more lead than me for the same purpose.

It's all here, in the cylinder section.

TECHDIVINGLIMITED.COM

 

[nereas]

Most of you have the chart already. It should help the decision-making process. I take off four pounds of lead to go from AL to a Faber FX-100. That still leaves 12 to ditch in salt water. My pal has Worthington 100's and takes off more lead than me for the same purpose.

It's all here, in the cylinder section.

TECHDIVINGLIMITED.COM

VERY NICE updated table, Stu, thanks!

 

[nereas]

Let's see...

A single AL80 has a buoyancy swing from -1.4lb to +4.4lb. I wore somewhere around 20lbs of lead with a 7+mm suit (Polar Tri-density 6/7/9) and a 6lb backplate. At the end of the dive, I am neutrally buoyant at 10 feet with 500psi in my tank and no air in my BC. That means I am 5lbs negative at the start of the dive (plus whatever suit compression).

A single X7-100 has a buoyancy swing from -10lb to -2.5lb. I wore about 14lbs of lead with the same suit and plate. Again, I am neutral at the end of the dive...so I am 7.5lbs negative at the start (plus suit compression).



That is a WHOPPING 2.5lbs difference. Think I can swim that up? You bet. Even considering a total BC failure, I can swim against it and get to the surface where I can ditch my weight belt. Then I'll be really positive.


References:
Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan
Scuba Tanks, Aluminum 80's, Pony Bottles, Spare Air Bottles, Steel Cylinders

It really depends on whether one or both of your legs is cramped also. And if so, then you can "swim up" -0-. And then you would die. RIP.

Then your buddies will probably split up your gear.