weight difference AL80/Steel

[spectrum]

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.

Thanks for the kind words. I'm just trying to give back some of what others helped me learn here on Scubaboard over the past year. It's not the sort of detail that dive classes seem to get into.

Now if the price premium on the E7-100s weren't so high..... :11:

Pete

 

[cummings66]

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.

But would it always make sense? For me I wear 8 lbs of lead weight with an AL80, if it is as stated with steel then I'd need 1 lb of lead. That's not a lot to dump.

 

[Orlando Eric]

Yeah Aluminum tanks are awful. You can't trust them. Evil things. You better send them to me! I will keep them locked up where they can not hurt anyone.. Especially those AL 100' s!

Eric

 

[wolves64t]

I think the biggest advantages of steel tanks are seen in cold water where you have to wear a lot of weight in order to compensate for the amount of insulation you need. The difference between eight pounds and one pound may seem meaningless to you but the difference between twent-four pounds and sixteen may make a huge difference to someone else.

 

[docmartin]

But would it always make sense? For me I wear 8 lbs of lead weight with an AL80, if it is as stated with steel then I'd need 1 lb of lead. That's not a lot to dump.

sounds like you are talking about warm water diving. you should be able to swim up an AL80 plus 8lb of lead. if you are, then no worries about the equivalent steel with 1lb of lead. if you are not (this is unlikely) then it would be an issue that you don't have ditchable weight.

 

[docmartin]

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.

this analysis is right on. however, it holds only true for the E7 80. the PST tanks are very light relative to their volume. for an LP steel tank such as a Faber the weight comparison does not hold true. they are heavier on land at 33lbs for a Faber 85. however, under water they are neutral when empty. so you save 4.4lbs in lead over an aluminum 80. subtracting the 1.6lbs weight difference on land you still come up ahead schlepping your tank to the shore but not by as much as with the E7 80.

 

[cummings66]

Yes, I've been in warm water for the 8lbs of weight

I call water warm if it's above 65 degrees f.

To be honest, I think it would be nice to only have one extra lb of weight to carry, it would make things a little nicer, but 8 lbs isn't much and for that matter 16 isn't too bad either. A 7mm suit with 8lbs for cold water would be nicer of course.

 

[spectrum]

this analysis is right on. however, it holds only true for the E7 80. the PST tanks are very light relative to their volume. for an LP steel tank such as a Faber the weight comparison does not hold true. they are heavier on land at 33lbs for a Faber 85. however, under water they are neutral when empty. so you save 4.4lbs in lead over an aluminum 80. subtracting the 1.6lbs weight difference on land you still come up ahead schlepping your tank to the shore but not by as much as with the E7 80.

You're right that the numbers work the best for the E7-80. The E7-100 is less dramatic but still comes out favorable to an AL-80 and gives you 22% more breathing gas. The biggest point is that it's really nice to have a tank that does not go positive and thus require weight for it's own sake. The lighter dry weight (walking across the beach swimming mass) is the next advantage. This will vary as you grind through the LP, MP and HP offerings. Some old Scubapro branded MP 72s were something like 8.5 pounds negative when empty! Like most things generalities are dangerous so run the numbers for whatever you're considering.

I also agree that as exposure protection goes down the criticality goes down. The buoyant aluminum cylinder does have advantages for diving wet with doubles or as stage bottles where negative steels would be too much of a good thing.

Pete

 

[cmalinowski]

Isn't just the difference in bouyancy characteristics that you can adjust? I mean all things being equal, if an al80 is +4lbs at the end of a dive and a steel whatever is -1, then I can remove 5lbs from my weight belt. It is that simple, is it not?

 

[teknitroxdiver]

Yep.