Extending bottom time with AL80s

[vinegarbiscuit]

If you want to keep your AL 80s, then a side mount set-up is one way to go. That will probably entail ditching your current BC, though, and configuring a dedicated harness (Nomad, Armadillo) for your side mount set-up. The only side mount divers I've encountered have been in the caves - some use side mount out of necessity, because some cave systems can't accommodate a back mounted diver. Others balk at the thought of strapping doubles on their backs and trudging down the steps with a pair of steel tanks and simply carry their AL80s down to the water one at a time. Either way, a side mount rig will give you all the redundancy of steel doubles with a lower risk of hernia!

The only other option is, I think, is to either double up your AL80s (which some people quite like - others do not, owing partly to buoyancy issues as the tanks are breathed down) or ditch them completely for a set of steel doubles. Again, that will entail ditching your BC. Final analysis - no matter what option you choose (keep the Al80s or ditch them for steel doubles), you'll need a new BC, either for side mount or doubles diving.

 

[Blackwood]

Go Side Mount - Steve Bogaerts

 

[DCBC]

I agree with Doc, buy a manifold and band the cylinders to increase your back-gas capacity. The other 80's can be used later as required as a traveler on the stage, as a bail-out or on the tree for decompression. You will always find uses for extra 80's, but increase your back-gas capacity first.

 

[DandyDon]

Other than that, the world dives on AL80's for a reason.

Other than standardization for the supplies, what's that? Many of us don't get as much time from a tank as you.

 

[Seaduced]

Well I do have 6 AL80 so I don't have to run to the store to fill them in for a week during my local diving at the quarry (usually 4+ used over week).

I do have 19cf pony with regulator set already. So really with exception of making a sling for 80cf my investment is rather minimal.

Yes it is a bit of task loading as I would have to breath down both about equally. But my first idea was just to use it descending down the anchor line, leave it at the bottom, do the dive and return to the anchor line and use sling bottle for travel up.

If we accept the minimal investment idea, why don't you just sling the 19cf, breath it down, then switch to the 80cf and finish the dive. That gives you nearly a 100cf, on board. The dicey part is getting near the end of the 19cf, if the 80cf is unavailable, you need to have enough to bailout.

Leaving an 80cf at the anchor, means you have to assume it won't be there when you return. There are many scenarios why it might not be there, slim chances, but possible. Unattended, the reg free flows, boat slip anchor, boat has to leave, good Samaritan retrieves lost tank, current prevents you from retrieving it, etc, etc. For planning, it becomes descent gas only. I wouldn't be comfortable leaving it behind and expect to use it later.

 

[Cave Diver]

Some good advice here so far. Some other considerations to throw in to the mix is the increase in weighting to accommodate the buoyancy swing from two tanks and what your procedure will be for air sharing in an OOG emergency.

But my first idea was just to use it descending down the anchor line, leave it at the bottom, do the dive and return to the anchor line and use sling bottle for travel up.

Realistically, how much gas would this actually take? Hardly seems like it would be enough to warrant an AL80, unless you have a deco obligation to fulfill on your ascent. If that's the case, I'd want my extra gas with me for the whole dive, not left on the anchor line.

 

[DandyDon]

If we accept the minimal investment idea, why don't you just sling the 19cf, breath it down, then switch to the 80cf and finish the dive. That gives you nearly a 100cf, on board. The dicey part is getting near the end of the 19cf, if the 80cf is unavailable, you need to have enough to bailout.

You don't dive a 19 cf pony do you? I certainly hope not that way. Not appropriate, and besides - many shops charge the same for filling one.

Realistically, how much gas would this actually take? Hardly seems like it would be enough to warrant an AL80, unless you have a deco obligation to fulfill on your ascent. If that's the case, I'd want my extra gas with me for the whole dive, not left on the anchor line.

Yeah really. I breath my back gas, carry my pony for emergencies, period. In Coz, I pay and extra $5/tank for 100s.

 

[Seaduced]

You don't dive a 19 cf pony do you? I certainly hope not that way. Not appropriate, and besides - many shops charge the same for filling one.

Hey Don, I was speaking to his suggestion.

The OP suggested using his 19cf pony reg to build an 80cf "pony" to extend his dive. Leaving the 80cf on the anchor after descent and pick it up on ascent. Makes more sense to me to breath down the 19cf and keep it with you.

But to answer you, no that is not how I would use a pony, it's for bailout, not dive extension.

Darell

 

[DA Aquamaster]

If a diver is using a stage on a deep OW dive, the common practice is to breath the stage down to a couple hundred PSI then switvch to back gas. You could do the same -with one vital difference. Divers using stages have redundant doubles so if the rpimary back gas reg fails, they have a back up. That would not be the case for a single tank diver, so if you switched from the stage to backgas and had a failure, your are pretty much SOL. So you would have to modify the practice to ensure you always left enough reserve in the slung 80 to ensure you could surface in the event of a back gas failure.

Potentially, you could leave 800 to 1000 psi in the stage (about 20 -25 cu ft) for a reserve. That would give you 50 cu ft off the stage, and then 77 off the back gas for a total of about 125-130 cu ft. The downside is that the slung AL 80 with 800-1000 psi will start to get light in the tail and the streamlining is poor so keeping it the whole dive is less than fun.

A better approach is to just double the AL 80s either with a manifold or as independent doubles in a set of travel bands. The latter is fairly easy to do and lets you gas manage them as truely indepndent doubles with sufficient reserve in either tank or as an 80 with an 80 cu ft pony. But in both cases the BC needs to be stable enough to handle the doubles. Side mounting is really just a subset of independent doubles with a different form of BC and of carrying the tanks.

With back mounted gas there is also the issue of twice the swing weight and the possible need for redundant bouyancy in the event the BC fails. That is less of an issue with a slung stage.

All that said, Doc is exactly right, it gets interesting when something goes wrong and you have to carefully consider the entire configuration as a system that works not only when it all works but when something goes wrong.

 

[divin'dog]

The problem with convoluted approaches is not when things are going well. The problem emerges when things go to hell - current blows you off the wreck and you're on the sand attempting to swim back in the lee of the hulk; you miss the upline in bad vis and have minutes to find it or go to Plan B; someone's reg craps the bed and now you're donating to someone while aborting the dive winging around a slung 80 off your BC - and things continue to go further off-plan. That convoluted setup now - instead of being helpful to you - adds to your task loading...

I have to agree with Doc... It's great when everything goes according to plan. When it doesn't and you're having problems from your jury-rigged equipment setup and/or unforeseen environment situation, and you're down at 130', the last thing you're going to care about is how much money you saved on your setup.

An additional task load may not seem like much now, but wait until there's a problem or series of problems down deep... i.e. your buddy is entangled... there's a stiff current... and you're both getting low on gas... Chances of this happening are probably slim but why add one more thing to take care of in a potential problem situation? The one thing you have control of before you get in the water is your equipment. Do it right now so you hopefully won't regret it later.