AL80 Doubles...Worth It???

[Michael Guerrero]

Hey All,

I'm considering buying a set of AL80s to use as doubles. This would serve as both a rec setup and tech as I move into deep air and deco diving. I plan to dive these in lakes/quarries and ocean/wreck, but no caves and likely no team diving.

I have a couple concerns. First is the volume. If using 3rds, it's only 100 cu ft, vs. the 130 cu ft I'd get from steel 100s. I supposed I could always sling a stage bottle for extra bottom gas (I think this is what the DIR guys advocate).

Second concern is trim. Based on the numbers I've found it looks like the tanks will be a few pounds negative w/ 50 cu ft left considering the bands, manifold, and regs. However, I'm concerned about going from a feet heavy attitude at the start of the dive to a feet light attitude at the end when most of the gas has been consumed.

I would be diving these dry and wet, but it's the wet that really is the concern.

Appreciate any inputs.

Mike

 

[boulderjohn]

Choosing the right size tanks is really a challenge. I don't think it is possible to pick a size tank that fits all situations. If you max out the volume of gas available, you will get very heavy tanks that offer a lot of resistance. Smaller tanks have less volume, but the ease of diving may increase your SAC rate enough to make a difference.

I have a set of twin steel 108s that are very nice for long Florida cave dives. If I am doing a deco dive in the ocean, though, the extra volume often does me no good because my buddies have smaller tanks and we plan on their volumes. This means I am struggling with clumsy, heavy tanks for no benefit.

I would like to give you a quick, easy answer, but I don't know it.

 

[PfcAJ]

al80s wet are awesome. rules like 'thirds' for OW can be overly conservative in some instances and overly aggressive in others. I suggest reading about the concept of 'minimum gas'.

 

[rongoodman]

They're all you'll see in the Mexican caves(not counting the SM rigs). Adding a tail weight helps with the trim when they start to go tail light. Adding a stage for extra gas is no problem, and they're considered safer for wetsuit diving by several tech agencies. An alternative might be Faber LP85s, especially if you can find a local shop who will overfill them.

 

[Michael Guerrero]

Thanks. 3rds is definitely conservative for OW, but I'm also looking at wreck pen, which is why I am thinking about it. Will look into the minimum gas thing.

Anyone have thoughts on trim? Anyone actually dive AL80s wet that can tell me if they noticed what I'm describing (start foot heavy, end head heavy)?

 

[rongoodman]

They trim out fine for me in a wetsuit with a few pounds as a tail weight. I'm not sure why you think they would start out foot heavy. I agree that an understanding of minimum gas is more useful than just "thirds".

 

[Instructor_Tom]

"personal Opinion"

I would not double up AL80s, I can get the same gas fill in a single LP108 that you will get from your double AL80s.

if you are really looking for more bottom time and getting in to stage decompression look at LP tanks to double up. Even LP95s will give you 108cft of gas per with a proper 3000psi fill.

also the LP tanks have a better trim configuration and don't go tail light to an extreme like AL will.

as stated this personal opinion.

T.


Sent from my iPad using Tapatalk HD

 

[Michael Guerrero]

I guess it's because of the tendency of ALs to turn valve down when empty. Any weight I use to offset that (tail weight, strap a weight to the tank, etc.) I'm thinking may cause me to have too much weight toward the feet until I've consumed enough gas for them to be back in balance. Maybe it won't be a big deal and something I can manage w/ the bubble in the bladder. I just don't have experience with it.

 

[PfcAJ]

The butt light thing is really inconsequential in my experience. You dive the gear, the gear doesn't dive you.

A single steel doesn't give you the redundancy needed for technical diving. 2/10 would not dive.

 

[rongoodman]

I think you'll find that any set of doubles is going to be head heavy, it's just that the Al80s might be a little more so when empty. It's pretty typical for new doubles divers to want to be "head up" to compensate for it.