Difference between Double steels & AL 80's

[tstormdiver]

I've got a chance to cave dive in Mexico after the first of the year (super excited!!!!). I've been told they primarily dive doubled AL80's there. I have dove singles AL 80's & double 85's, 95's & 108's . For those that may be familiar, what are some differences in trim & weight? In MX, I will be diving a 7mm wetsuit. In a 5mm wetsuit (same as the 7mm) & a single AL 80, I typically wear 16# weight & do fine,.... in doubles I use no weight. I know there is typically a swing of about -2 lbs to + 4lbs when nearing empty. Is this even worse when they are doubled? I am hoping to be able to try a set out at the quarry, but because of temps will have to dive dry in heavy undies (sorry,... I'm a warm water wuss). I'm just trying to get a basic understanding of how weighting & trim will be affected. Thanks....

[TSandM]

Tammy, can you get to a pool? You really need to find this out in the exposure protection you are going to use.

Double Al80's with bands and manifold and two regulators, are somewhere close to neutral when empty. But they are also profoundly butt-light. And in MX, you have to weight yourself for moderately salty water, because you WILL need to be able to descend through the halocline.

I use 7lbs with a dry suit and thin undergarment and double Al80s, but I have to hang the whole 7 lbs off the bottom bolt to be in balance when the tanks get low.

[maus711]

tank-specs-format-for-logbook.xls

Take a look at the attached tank weight characteristics and plan your weight requirements. Then trim to suit your needs.

Mike

[Dive-aholic]

The first time we went to Mexico my wife and I were still backmount. When we used AL80s (there are some steels down there) we just used 4lb V-weights and we were fine. We were diving 7/5 wetsuits with 1mm skins.

[tstormdiver]

Tammy, can you get to a pool? You really need to find this out in the exposure protection you are going to use.

Double Al80's with bands and manifold and two regulators, are somewhere close to neutral when empty. But they are also profoundly butt-light. And in MX, you have to weight yourself for moderately salty water, because you WILL need to be able to descend through the halocline.

Something happened to my post when I went to edit it....

Unfortunately the pool with the wetsuit is not an option. No one at my LDS has any doubled AL80's (everyone dives steels). I have called & asked around. An out- of- town friend has offered a set for me to try, at a big get- together in late Nov. By then the water will be much to cold (for me) to dive a wetsuit of any kind. I can either dive the wetsuit at home with steels (which really doesn't help me) or dive the AL80's at the quarry with my thickest undies (650gm). I'm guessing those thicker undies will be close to, or more buoyant than the 7mm wetsuit. Being a bit negative (as long as I'm balanced) shouldn't be a huge issue for me. I do have 5# & 7# V-weights & a 5# tail weight to play with. I plan to dive them both full & then drain them to <500psi to get a good idea of the buoyancy swing.

[TSandM]

Well, you could take a single tank setup into the pool in your wetsuit, and in your drysuit with the thick undies, and see what the weighting difference is. Then you could weight yourself with the Al80s and thick undies, and subtract the difference for MX.

I think you're going to find something in the 5 to 7 lb range will work, but again, be aware they are very butt-light when low!

[Dive-aholic]

Something happened to my post when I went to edit it....

Unfortunately the pool with the wetsuit is not an option. No one at my LDS has any doubled AL80's (everyone dives steels). I have called & asked around. An out- of- town friend has offered a set for me to try, at a big get- together in late Nov. By then the water will be much to cold (for me) to dive a wetsuit of any kind. I can either dive the wetsuit at home with steels (which really doesn't help me) or dive the AL80's at the quarry with my thickest undies (650gm). I'm guessing those thicker undies will be close to, or more buoyant than the 7mm wetsuit. Being a bit negative (as long as I'm balanced) shouldn't be a huge issue for me. I do have 5# & 7# V-weights & a 5# tail weight to play with. I plan to dive them both full & then drain them to <500psi to get a good idea of the buoyancy swing.

For weighting purposes get in the pool in the suit you plan on diving and your doubles BP/W with a single AL80 on the back. Clip another AL80 on as a stage. This won't help with figuring out with trim but you'll at least have your weighting figured out and can move it around as necessary once in Mexico.

[Lobzilla]

Tammy,

I dove AL80 doubles off West Palm Beach with a 7mm wetsuit, AL backplate (for travel) and a 6# soft V weight.

team.jpg

You can ask elvisisalive, the diver on the right, what he used.

With drysuit I use a 4# soft V weight and a 7# tail weight in fresh water and another 5# on the waist belt in salt water.

I disagree with Lynne on the problematic trim characteristics of the tanks. AL80 doubles is the "go-to" choice if 150cuft are enough for the Eastern GUE crowd. I also dove AL80 doubles dry on Vancouver Island this summer and they got along with the PNW waters just fine . When Bob Sherwood recommended AL80 doubles I thought he was kidding but they are now the gold standard I measure everything else against in terms of trim. Just got myself another set of Catalinas in "dirty bastard" finish and Bob is showing off a pink set these days.

Sherwood_DiverRescueDemo.jpg

Ask whether they have lead shot (pellets) where you are going and then bring two or three of the soft v weights from XS or Highland. Due to the length of the AL80s you can use these pouches as V weight, tail weight and even double tail weight if necessary. The short and square tail weight pouches do not work as well on AL80s IMO.

[idive2]

I don't dive doubles or caves so I cannot comment on that. I can say though the one thing I notice when
switching from my single steel LP85 to an AL80 is a light lifting type effect on my jacket BC as the tank gets
below 1000 PSI. Even when I have added the extra weight for the aluminum tank to the BC I still feel this
effect especially if my BC is not real snug. The V weights that the doubles divers are using probably would not
produce this effect. The steel tank tends to stay negative and I become familiar with an ever present weight there
and when it is not there I do feel the difference. Also the AL80 when compared to say an LP85 will be lighter at the
bottom. My trim is always a bit better when using the AL80. It is acceptable with the LP85 but I can feel the difference.

[parzdiver]

I have some experience switching from a single AL80 to double AL80's during a couple trips. Generally, I feel the switch between the tanks didn't need any adjustment in additional ballast. The additional positive buoyancy of the second tank is essentially offset by the negative buoyancy of the bands, manifold and extra regulator. I was able to breathe the doubles down pretty far and was neutral at the last deco stop.