weight difference AL80/Steel

[all4scuba05]

help me understand this...I weigh 140 lbs...my legs are the strongest part of my body but not like a muscle head's...AL80's make it so i have to wear 20 lbs...I do mostly beach dives...why should I use Steel tanks? all I hear is that it lets me take weight off my belt...what good is that if the steel tank is now heavier than the AL80? Seems like all I did was move weight from my waist to my back...

Once i'm in the water, it all weighs the same...after all I make sure I'm neutrally bouyant...so as far as weight is concerned...when i'm walking to and from the beach, is when I feel the workload...

just want to understand the theory better because i'm about to switch to steel...

 

[xSandman3]

You have to carry extra weight to compensate for the positive buoyancy of an empty AL80...up to 5lbs or so positive. Most steel tanks are neutral or slightly negative at the end of a dive. You're right, walking across a beach at the beginning of a dive is pretty much the same regardless of tank metal, but there is a really noticeable (to me) difference when you're walking back after the dive.

 

[rjchandler]

Seems like all I did was move weight from my waist to my back...

...

Correct. This will affect your trim both underwater and on the surface. Some people really hate weight belts - the less on the belt the better. On that hike across the beach having your shoulders take more of the load will feel better. You also made more of your weight non-ditchable. YMMV

 

[gfisher4792]

From the DiveRite website:

Cylinder Serv.
Press. Dia. Height Weight(lbs.) Buoyancy (full:empty) (lbs.)
E7 Steel 80 3442 7.25 20.00 28.0 - 8.5 : - 2.5
Aluminum 80 3000 7.25 26.10 31.4 - 1.4 : + 4.4

So, actual weight-wise, a steel tank is lighter (due to AL needing thicker metal to handle the pressure). And like xSandman said, you have a big positive buoyance swing near the end of a dive that you have to be weighted to compensate for. Simplistically, you can wear ~6 pounds less lead with a steel than an AL.

EDIT: Stupid formatting! Anyway, weight is 28 lbs. steel, 31.4 lbs. AL, and steel's buoyancy is -2.5 pounds empty and AL is +4.4.

 

[teknitroxdiver]

What that (^^^^^) means is that not only is the tank 3.4# lighter, you can take almost 7# off your weight belt. So, you walk to the water with 10.4# less weight on your back and hips.

 

[all4scuba05]

ok...now it makes sense...maybe my friend had a larger steel than my AL80...because when i lifted it up with BCD and 6lbs of weights, it was definitely heavier than my AL80 setup.

 

[JeffG]

ok...now it makes sense...maybe my friend had a larger steel than my AL80...because when i lifted it up with BCD and 6lb of weights, it was definitely heavier than my AL80 setup.

It could very well be...don't confuse dry weight on land with buoyancy characteristics in the water.

 

[spectrum]

ok...now it makes sense...maybe my friend had a larger steel than my AL80...because when i lifted it up with BCD and 6lbs of weights, it was definitely heavier than my AL80 setup.

See this recent post of mine:
http://www.scubaboard.com/showpost.php?p=1191538&postcount=16

Pete

 

[BrianS]

I personally prefer more weight over my shoulders/back than a weight belt on my hips.

 

[all4scuba05]

spectrum and teknitroxdiver...you both should be a teachers...you explained it exactly how it needs to be told to clear up all the confusion. For once someone knows how to present the evidence that steel makes sense.