Doubling AL80's, bad idea?

[kidspot]

xScubaStephx - It's partly a matter of philosophy - Militant Medic, and several of us others out here who subscribe to the DIR philosophy of diving, don't like the problems a double bladder can bring to the game, so if not diving a drysuit we avoid diving a rig which would get the upper hand on us in the event of a wing failure. Usually this means sticking with AL80's (or bouyant steel tanks like lp72's) instead of heavier steel tanks. If you are doing dives which require more gas than a set of doubled up AL80's provides, you'll probably be looking at a good deal of deco time, which means needing the extra exposure protection a drysuit offers... If you do a search for "balanced rig" there's a lot of info out there.

Dhampton - a set of double AL80's will be a good way to get into doubles, not overly large, and since you're a smaller person I'm assuming you'll get lots of bottom time off them. If you're diving does not require larger steel tanks, why not start with AL80's and then if you need them later get steel doubles and convert the old AL80's to dive singles or large stage bottles. AL80's are quite versatile, and if you've already got them ... why not use 'em.

I found there's not much additional weight required for my double AL80's because the isolator bar, extra reg and bands add up to about the same amount of weight the extra AL80 requires... so not a lot of difference.

Of course first of all, decide why you're wanting to dive doubles ... lots of expense beyond just the tanks (though with steel tanks that's a big chunck of the expense) For me it was partially needing the extra gas to keep up with my smaller dive buddies, partly because I wanted to learn something new, and mostly just curiosity

Aloha, Tim

 

[DivingCRNA]

Steel tanks remaining neutral near the end of the dive is a plus.Then you wouldnt need any weight.

Steph-

ALL tanks are more bouyant when empty than when full. AL 80 tanks just happen to float on their own (barely) when empty, or near empty.

Depending on the divers overall weighting and bouyancy of themselves and their gear AL 80s might be perfect for a given diver.

For example: I dive a BP/W with a 6 lb steel plate and a 2 lb STA. In a 3 mm wetsuit with an empty BC I am slightly negative. Not so much that I cannot swim to the surface in the event of wing failure, but negative none the less. At the end of the dive I am neutral. If I wear a steel tank, I am really overweighted without any lead on. I am more bouyant at the end of the dive, but still fairly negative. If I have to do an ESA, I can doff the BP/W very fast: One buckle and ditch the shoulder straps. The wetsuit them makes me positive.

In a 3 mm neoprene drysuit I wear 12 lbs of lead with an AL 80 tank. Not what I would consider a big sacrifice. I might even get away with the same lead if I doubled 2 AL 80s because of the weight of the manifold, bands, and such. But I have not seriously looked at it yet. I might next summer if I do Tech 1. It depends on my objectives.

80 cf of air weighs the same no matter what tank it is in. You have to account for the loss of the mass of the air in your dive plan no matter what.

 

[SparticleBrane]

I think that there are some cases where diving steel doubles with a wetsuit would be fine. I understand (and agree with, for the most part) the DIR redundant inflation idea if you dive heavy steel doubles. However I believe there are cases where you just need to think about the situation.
If you're ocean diving or cave diving with heavy steel doubles--definitely use a drysuit for redundant inflation. If I'm using heavy steel doubles for a quarry dive where I MIGHT hit 30ffw (with a shovel), or a shallow river dive, then I just don't see a need for a drysuit as redundant inflation. A wetsuit would suit my purposes perfectly well.

 

[Scared Silly]

I just doubled up a set of Al80s. For my open water diving they fit the bill as I need only 4-6lbs of extra lead to offset for my drysuit and be neutral at the end of the dive. When diving warmer waters and wet (3mm/4mm suit or thinner) I am over weighted by around 6-8lbs. Which in the case of a wing failure I can swim that up if necessary. With HP80 steels I would be over weighted by over 20lbs which would mean I would be fish food unless I had a backup such as lift bag or SMB.

Check out the wing calculator that is now stickied in the BC section. This will give you a really good idea of what different cylinders will do for you in different suits.

 

[xScubaStephx]

Ok then what does DIR find wrong with a dual bladder wing?Im sure if I dug around I could find out but my shovels dull today.

 

[mike_s]

Ok then what does DIR find wrong with a dual bladder wing?Im sure if I dug around I could find out but my shovels dull today.

I doubt that DIR would approve of AL80's doubled also... I dunno... I don't drink that DIR kool-aid religously.

Stephx, if you're looking for doubles, since you 16 and presumably not large/builky like many your age, you might consider a set of older steel 72's or HP80's instead of AL80's as doubles. the double 72's would be cheap to do, more compact for your size, and easier to manage and would most likely cover all your air consumption/volume requirements. just an idea.

 

[kidspot]

here is a recent thread dealing with the issue a "little bit" http://www.scubaboard.com/showthread.php?t=158747

 

[kidspot]

I doubt that DIR would approve of AL80's doubled also... I dunno... I don't drink that DIR kool-aid religously.

Actually they do

Stephx, if you're looking for doubles, since you 16 and presumably not large/builky like many your age, you might consider a set of older steel 72's or HP80's instead of AL80's as doubles. the double 72's would be cheap to do, more compact for your size, and easier to manage and would most likely cover all your air consumption/volume requirements. just an idea.

I agree - lp 72's make a really nice set of small doubles, great for starting out with, or for smaller folks.

Aloha, Tim

 

[xScubaStephx]

ok ive read the advantages and disadvantages of a dual bladder.My dad removes his bungee with doubles and puts it back on for a single tank.He also only has one lp hose going to the left side.He told me if he has a blowout,he can orally inflate the right side enough to get off the bottom till he gets the lp hose connected.Hes NSS-CDS and NACD,and wont comment on DIR,except for to each his own.Opinions will vary on any forum,in the end I think its up to you.

 

[SeanQ]

There are several different types of steel 72's out there as well. I have a set of 2475psi 72's made by Norris in the 1970's. Although I haven't tested them they feel slightly negative. I think Faber and PST make 72's as well in 3300psi and 3442 versions.