Diving with twin Alum 80's

[Underwater Ninja]

So DMX, I'm going to plop this question here because I'm sure the answer to my question will deal more with what type of BCD or backplate I'm using than anything else so here goes...

I am thinking about trying out diving with twin 80's. Other than the valve setup what else do I need? I've never dove with twin tanks before so any information/experience you could throw my way I would greatly appreciate.

~Lewis

[rjack]

Manifold & bands
a second 1st stage
5-7ft hose
24" hose
some sort of wing, ~40lb lift would be appropriate
either steel or aluminum plate (or one of the softpak harness systems) depending on exposure protection

What exposure suit are you using?

An understanding of how doubles fills/valves can be completely FUBARed and kill you. Worst would be either filling the tanks with the isolator closed or diving with it closed.

A single steel hp130 is almost the same volume of gas and alot simpler.

[KMD]

So DMX, I'm going to plop this question here because I'm sure the answer to my question will deal more with what type of BCD or backplate I'm using than anything else so here goes...

I am thinking about trying out diving with twin 80's. Other than the valve setup what else do I need? I've never dove with twin tanks before so any information/experience you could throw my way I would greatly appreciate.

Lewis,

You are going to get a ton of information your way shortly. Will have advice on all sorts of tanks. Each person liking different types/disliking certain types. To a large extent all the advice is correct as it deal with the users specific knowledge and diving style and all the advice is wrong, as it will not deal with your local area and diving style.

so with that said probably the best bit of information/experiene I could throw your way is: Get a good local mentor and or take a class regarding it. GUE and UTD both offer small 1 or 2 day classes that cover doubles. If there is one in your local area consider talking to the instructor regarding it.

With that said internet diving wise you can break down the knowledge/skills you need into several broad catagories:

Tanks - Covering everything from the correct/recomended tanks for your area to what the various pieces of the tanks are and do. For a basic setup you will need 2 tanks, a manifold and a set of bands. Knowledge on how to break down and setup your tanks would be a plus as some store operators will not do so for hydro/vip.

Gear selection - Do you have the proper wing & backplate for the doubles set?

Regs - How to properly setup your Regs on your doubles such that hose routing is clean. Knowledge of why we put which hoses on which posts is important as it has an inpact on our responses to emergencies.

Skills - Being able to manipulate the valves in a considered manner below and above the water. Its important to know what the effect of shutting off a valve is on the rig. Unlike singles when you shut off your valve everything stops working, with doubles, only parts of your rig stop working. Its important to be able identify this intuitively when under the water. Its also important to know the effect of shutting off certain valves above the water as it can be very dangerous to get a fill with certain valves closed.

[scubainchicago]

So DMX, I'm going to plop this question here because I'm sure the answer to my question will deal more with what type of BCD or backplate I'm using than anything else so here goes...

I am thinking about trying out diving with twin 80's. Other than the valve setup what else do I need? I've never dove with twin tanks before so any information/experience you could throw my way I would greatly appreciate.

~Lewis

Also, if your thinking about doubling up a set of existing tanks you already own, make sure that they are identical manufactures, alloy, and have an equal height........

[rjack]

Also, if your thinking about doubling up a set of existing tanks you already own, make sure that they are identical manufactures, alloy, and have an equal height........

Why?
Catalina's and Luxfers can be doubled up together no problem. Likewise 6351 and a 6061 alloy tanks. With modern bands, slight height differences (rare in AL80s anyway) just mean you need to be more careful to not stress the manifold until the band bolts are locked down. And tolerate a bitt of wobbly when standing them up since the bases won't be aligned.

[PeteJ]

Asking the question on aluminum 80's is a very good place to start for any diver moving into doubles.

Sure there are other single tanks with just about the same capacity, but don't let anyone convince you that you never need to know about how to use double aluminum 80's.

1) Sooner or later you will travel to an area where these other tanks are not available and if you want/need to go deeper/longer and need more gas, double aluminum 80's may be your only choice.

2) The other reason is that if you progress further into deep/long dives a set of aluminum 80's can be broken down into your stage bottles and the manifold etc. reused with larger capacity tanks.

I find that double luxifer aluminum 80's fully dressed out with back plate, regs, bands, and manifold will be right at neutral (or close to it) at 400-500 psi. They will want to turn bottom up which can be annoying to some, but a 3# weight zip tied between the tanks at the bottom will trim them out nicely. Then it is only what you need to get neutral with your exposure protection system (T-shirt and shorts, wet suit, dry suit, etc.).

[Underwater Ninja]

Wow thanks everyone so far for you wonderful responses.

KMD - Roger all. I wish I was near a GUE or UTD shop to get those lessons but I'm not. I do have a local PADI Instructor that I plan to talk to who does tech diving as well but I wanted to get information from more than one source.

RJack - I agree that a single steel could do the same job but I considered this task/challenge a way of accomplishing what I need (more BT) and an entry into a tech setup.

PeteJ - That's a good tip on the zip tied weight. I would have never thought of that!

[scubainchicago]

Why?
Catalina's and Luxfers can be doubled up together no problem. Likewise 6351 and a 6061 alloy tanks. With modern bands, slight height differences (rare in AL80s anyway) just mean you need to be more careful to not stress the manifold until the band bolts are locked down. And tolerate a bitt of wobbly when standing them up since the bases won't be aligned.

Sure, I guess you could pair up a HP steel 120 and an AL 80 as well and have them function......but in a perfect world it would be nice to have identical tanks that don't wobble and tip on land and have different buoyancy characteristics in the water.

[b1gcountry]

Honestly, the easiest way is to make friends with someone who dives them somewhere near you, then bug them about letting you try them out.

Tom

[KMD]

PeteJ - That's a good tip on the zip tied weight. I would have never thought of that!

One of the dangers of getting information on the internet. Zip ties can and will age and fail.

Pete could very well be situating his weight such that even if it did it wouldn't fall out. Or he is experienced enough that a quick lost of weight wont affect his total system. Or he has some meathods of gear maintenance that reduce/eliminate this likelyhood.

Once again I can't emphasize enough the need for a good mentor and/or training. It really will save you quite a bit of time banging your head against the wall.

Also, I don't know if your dive count in your profile is correct, but you mentioned you wanted longer bottom time. I have something that you can do that won't cost you anything and will increase your bottom time. That is dive!!! People sac rates usually greatly improve between 50 and 150 dives. Better sac will give you longer bottom time.

Kevin

[PeteJ]

Pete could very well be situating his weight such that even if it did it wouldn't fall out. Or he is experienced enough that a quick lost of weight wont affect his total system. Or he has some meathods of gear maintenance that reduce/eliminate this likelyhood.

Once again I can't emphasize enough the need for a good mentor and/or training. It really will save you quite a bit of time banging your head against the wall.

Well, zip ties are fast and dirty and get the job done, but UV will get after them over time. So, for a permanent attachment you could use a stainless steel hose clamp like on a stage bottle. Either way, if the loss of a 3# trim weight screws you up, then we need to have another talk.

The point of getting a diving mentor is well taken and should always be foremost. Training, instructors etc. are all fine, but mostly last for the duration of a class. A good mentor is much, much better because the mentor will be long term and eventually the student will become equal to the mentor to become a full team. I have been diving with the guy who was my mentor for over 20 years now. But now we are buddies.

Lets get back to the original post:

For the original poster, I see you location is in Italy just North of Napoli.

What type of diving do you want to do?
Why do you want to do it?
Where do you want to do it?
How deep are you thinking of going?
How long do you want to stay at depth?
What exposure protection do you have?
What exposure protection do you plan to have?

The answers to these questions will go a long way to tailoring the answers you will get. Someone diving in the warm waters of the Red Sea will have a completely different setup from a Northern Ocean wreck diver in a dry suit and heavy undergarments.

Aluminum tanks that are neutral at the end of the dive are great in warm waters, I used to dive the North Carolina wrecks in a 3mm shorty and a pair of painters pants. Never needed more then a 4# weight to hold my stops.

Steel tanks that are heavy at the end of the dive are great in cold water when you are trading weight on a weight belt for weight in the steel of the tanks on your back to counter a dry suit with thick underwear.
What exposure protection do you plan to have?

[Underwater Ninja]

One of the dangers of getting information on the internet. Zip ties can and will age and fail.

Yep. Fully understand. What I like to do is gather information on the internet which builds my vocabulary in that specific topic. Then I go and do some research using that newly developed vocabulary. THEN I go and try to find someone actually using the equipment and learn the physical task armed with this developed vocabulary and information. I guess too much academic research has ingrained this into my daily life.

Pete could very well be situating his weight such that even if it did it wouldn't fall out. Or he is experienced enough that a quick lost of weight wont affect his total system. Or he has some meathods of gear maintenance that reduce/eliminate this likelyhood.

He probably does. I definitely wasn't running out to zip tie some weights to my rig sorry if I gave that impression.

Once again I can't emphasize enough the need for a good mentor and/or training. It really will save you quite a bit of time banging your head against the wall.

Couldn't agree more.

Also, I don't know if your dive count in your profile is correct, but you mentioned you wanted longer bottom time. I have something that you can do that won't cost you anything and will increase your bottom time. That is dive!!!

I have 51 dives logged to date but my actual tasks usually involve a lot of exploration dives to find new dive sites and twin tanks were what I was thinking for longer dives not MORE dive time. Having a longer bottom time would allow for more costal/potential dive site exploration. I was not simply trying to "stay down longer".

What type of diving do you want to do?
Why do you want to do it?
Where do you want to do it?
How deep are you thinking of going?
How long do you want to stay at depth?
What exposure protection do you have?
What exposure protection do you plan to have?

I would definitely be diving cold water with an average depth of 40 - 60 feet (12m - 20m) and I dive with a full 5mm in the summer with an added 5mm shorty in the winter.

Thanks everyone for your answers so far. I guess I just asked the wrong kind of question. I was reading a post about how a lot of folks on this dive board were tech divers so I thought I would get the low down on the types of setups you use. I understand that a lot of that has to do with personal preference or situations (cold, warm, etc) and that *gasp* obviously some type of training should come into play before doing. I was just interested in that area but I can see that this question lends itself easily to getting off topic so I will explore this info elsewhere.

~Lewis

[LCF]

Well, UN, you just ran into one of the distinguishing features between recreational and technically trained divers. When you get into higher risk diving, you start to get very critical of your gear, because every gear choice brings with it advantages and disadvantages, and being unaware of the downside of a given choice can bite you in the butt, hard, in the wrong situation.

You will also tend to get much better (and nicer) information, when you define your problem carefully in your original question.

For the kinds of dives you are talking about -- shore diving in relatively shallow depths for long periods of time -- doubled tanks may not be as good a solution as they initially appear to be.

Advantages: Increased gas supply. Al80's are easily come by almost anywhere, and are relatively corrosion-resistant. In the world of doubles, they are light (but small in capacity) and they are not terribly negative, and are thus appropriate for use with wetsuits. They offer significant redundancy if you are practiced with valve shutdowns..

Disadvantages: Doubles are heavier and more massive, and make any kind of tricky entry or exit more difficult. There is significant expense involved in setting them up and acquiring a second regulator for them. Fills are expensive, unless you pay by the cubic foot for your gas. (Our shops charge double to fill them, and it doesn't matter whether they are empty or only half empty.) Isolators add a bunch of failure points and potential problems, including one (filling or diving with isolator closed) which can be lethal. Getting full benefit out of the redundancy they offer means spending a lot of time practicing shutdowns, until they are fast and smooth. Your buddies also need to be coached through how the whole setup works, in order to understand THEIR role in managing failures. And finally, doubles are increased mass and bulk, and take more energy to swim forward.

Mo2 and HBDiveGirl are the people I know who do the most diving similar to what you are describing. They tried going to double tanks a while back, and eventually concluded that using very large single tanks gave them the best of both worlds.

I am sorry that you feel you didn't get the information you wanted from asking here. I think you did get a lot of good information -- it just may not have been what you wanted to hear.

[Underwater Ninja]

You will also tend to get much better (and nicer) information, when you define your problem carefully in your original question.

Definitely. I will try to be clearer next time.

Advantages: Increased gas supply. Al80's are easily come by almost anywhere, and are relatively corrosion-resistant. In the world of doubles, they are light (but small in capacity) and they are not terribly negative, and are thus appropriate for use with wetsuits. They offer significant redundancy if you are practiced with valve shutdowns..

Disadvantages: Doubles are heavier and more massive, and make any kind of tricky entry or exit more difficult. There is significant expense involved in setting them up and acquiring a second regulator for them. Fills are expensive, unless you pay by the cubic foot for your gas. (Our shops charge double to fill them, and it doesn't matter whether they are empty or only half empty.) Isolators add a bunch of failure points and potential problems, including one (filling or diving with isolator closed) which can be lethal. Getting full benefit out of the redundancy they offer means spending a lot of time practicing shutdowns, until they are fast and smooth. Your buddies also need to be coached through how the whole setup works, in order to understand THEIR role in managing failures. And finally, doubles are increased mass and bulk, and take more energy to swim forward.

This would probably take away from why I would want to do this in the first place. Tank fills are already expensive.

Mo2 and HBDiveGirl are the people I know who do the most diving similar to what you are describing. They tried going to double tanks a while back, and eventually concluded that using very large single tanks gave them the best of both worlds.

I would probably come to the same conclusion.

I am sorry that you feel you didn't get the information you wanted from asking here. I think you did get a lot of good information -- it just may not have been what you wanted to hear.

Nah, I got a ton of amazing info. I didn't come with preconceived information so there was nothing to hear that I didn't "want" to hear. It was all great info.

Thanks a ton DMX!

[Saspotato]

Honestly, the easiest way is to make friends with someone who dives them somewhere near you, then bug them about letting you try them out.

Yea I really recommend this and as MANY setups as you can get your hands on. Not just tanks too, I tried a few different wings (including double bladder bungee wings to see that the deal was!) and a few different tank sizes. This is what I did and I am really glad I did so as if I'd gone with my first idea I would have had regrets (steel 55cf - my reasons where they were light, low air consumption, primarily shallow solo diving). I ended up going with twin steel 100cf and can do two decent dives off the one fill which is handy when fills are a long way away from the dive site and they also trim out a lot better. So it was great to get various loans off friends, and now I return the favour by loaning mine out to buddies

As far as what you need, I need the following for my twinset:

-tanks x 2
-new backplate (I was swapping my plate between singles and doubles rig but it was a PITA so I got another plate)
-manifold
-bands
-new harness
-new doubles wing (I got 45lb lift)
-first stage x 2
-second stage x 2
-SPG
-new hoses for: 7ft primary, 24" backup, new drysuit hose
-tail weight pocket
-another line cutter/sheath for my new harness

I think that covers it.

With learning about valve manipulation and so on, I had been taught by a friend how to do valve drills and the importance of flow checks. Though this ended up being taught to me in a class that I did recently, and the teacher also covered the nine manifold failures with kind of an interactive game during our theory work, and I found that really helpful, and then in practice we had to demonstrate valve drills as well as our response to valve failures in the water as he had an air gun he'd hold up to which ever post he wanted to fail. So yea, whilst I knew a lot of it already, I found the classwork stuff very helpful as well. If you don't have a friend that can show you the ropes, maybe something like 'Intro to Tech' or something might be helpful?

All that being said, with the depths you are diving to, if you are NDL buddy diving with trusted buddies then I don't see a great need for twins. I personally use them for solo diving, decompession diving, diving below 30m or overhead diving. Anything other than that I'll take a single tank as I don't like to dive with doubles if I can help it as they are heavy... And I guess this might not be a popular idea here but OW dives 12-20m I'd take a pony if I needed redundant air for bailout.