Going doubles - questions

[jduncan]

Lisa and I have deciced we are going to get a doubles setup. The reason is that we would like to start diving some of the wrecks around the NE area, and most diver operations require 30CF reserve gas minimum. After a little research we figured it would make more sense to start using doubles than to rig a 30 or 40CF pony bottle up. Since I don't have any experience in this area, I have some questions ...

We plan to stay within the NDL (for now)
We have a pair of HP100's and a pair of HP80's (Faber)
We are using DIN first stages
Both of us are using stainless backplates by OMS and DSS

My questions are (bear with me - this is new):

Do we need the manifold/isolator valves at all if we are going to use them as reserve source only? My guess is yes.

If yes - will we isolate the tanks while diving within NDL?

Are there considerations when buying a redundant first/second stage? Right now we are using GS200's and I would certainly prefer to buy a second set for the doubles.

From doing some research it looks like most divers remove the octo when using doubles, is this a fair assumption?

The computer (cobra) will be on one of the first stages - if the tanks are joined it will certainly throw off the SAC rate, but I would think that the NDL, and dive time would not be affected - any other issues with this? Maybe I don't even need to worry about it?

Assuming I use manifold valves, can I use the tanks in a singles setup without changing the valves?

Do most divers split the connection of drysuit inflater, BC inflator, and primary second stage between the two tanks? What's the best seup?

Thanks

Jeff

 

[Meng_Tze]

Lisa and I have deciced we are going to get a doubles setup. The reason is that we would like to start diving some of the wrecks around the NE area, and most diver operations require 30CF reserve gas minimum. After a little research we figured it would make more sense to start using doubles than to rig a 30 or 40CF pony bottle up. Since I don't have any experience in this area, I have some questions ...

We plan to stay within the NDL (for now)
We have a pair of HP100's and a pair of HP80's (Faber)
We are using DIN first stages
Both of us are using stainless backplates by OMS and DSS

My questions are (bear with me - this is new):

Do we need the manifold/isolator valves at all if we are going to use them as reserve source only? My guess is yes.

If yes - will we isolate the tanks while diving within NDL?

Are there considerations when buying a redundant first/second stage? Right now we are using GS200's and I would certainly prefer to buy a second set for the doubles.

From doing some research it looks like most divers remove the octo when using doubles, is this a fair assumption?

The computer (cobra) will be on one of the first stages - if the tanks are joined it will certainly throw off the SAC rate, but I would think that the NDL, and dive time would not be affected - any other issues with this? Maybe I don't even need to worry about it?

Assuming I use manifold valves, can I use the tanks in a singles setup without changing the valves?

Do most divers split the connection of drysuit inflater, BC inflator, and primary second stage between the two tanks? What's the best seup?

Thanks

Jeff

Good questions Jeff. Let me take a stab at them.

The principle of manifolded doubles is to have more gas and create redundancy. The tanks are joined with a manifold that is open during normal diving. If you would double up two AL80's you would get double the amount of gas to work with. The isolator valve is to separate the tanks in case of a failure in one of the valves. If a 1st stage gives you problems, you close that valve and you can still breathe gas from both tanks on the other regulator.

In doubles you need two first stages and two second stages. My advise would be to get good regs and maybe stay with the same ones you have. This makes stocking up spares easier and changing out things more practical. But technically you do not have to. Not sure what you mean by removing the Octo, but this is what the rig looks like.

Right post is primary reg and inflator hose. Left post is backup reg, optional drysuit inflator and spg. If you are going into overhead (inside the wreck), I would advise a long hose.

As for using the tanks for single tank dives.... impractical. Once the tanks are banded together with a manifold, they effectively become one large source of gas. It makes no sense to separate them, put different valves on for single tank dives. It would also put undue stress on orings, valves etc, to put together, take apart, put together etc.

Most people who dive single tanks as well as doubles have sets of tanks for both. But I promise you that once you get with doubles, you will most likely not go back to diving singles.

Gas management with doubles is the same, you just have more gas to work with.

You computer will still be working fine with SAC, there is no change in that in terms of how much you breathe/time unit. You just can stay longer. No issues there

If you want to continue diving singles and stay within NDL and see more of the wrecks, maybe a single tank with a pony would be a better solution to start with. You can always use the pony later as a deco bottle.


Hope this helps as a first stab at your questions.

 

[jduncan]

If a 1st stage gives you problems, you close that valve and you can still breathe gas from both tanks on the other regulator.

I see, so regarldess of whether the tank valve to the first stage is closed or not, gas will be flowing below the vave to the manifold. I don't know this.

By removing the octo I mean - Right now we have a 2nd second stage - an "octopus" for lack of a better term, on a yellow hose. With the doubles setup, I wouldn't need this correct?

If the plan is to stay within NDL, then will the doubles count as "backup" gas if they are not isolated? I would assume that having 160 to 200CF of gas on a dive within NDL, you would have plenty of reserve - will this take the place of a "pony tank"?

We thought about a pony rig, but after we spend the cash for the tanks, regs, and rigging, we are almost better off to setup the doubles. I'm afraid after a few dives with pony rigs, we'll wish we just went doubles.

Thanks for the reply!

Jeff

 

[timle]

disclaimer IDNDDY - I do not dive doubles yet

But from my understanding the beauty of diving manifolded doubles versus independent doubles is the most common failures you still have all your gas.

Doubles - unstoppable free flow - turn off that post - All gas still available through other post.
Independent - unstoppable free flow - turn off that tank - half gas available

First stage failure same, hose failure same, etc. Now if the tank, neck, or valve actually has trouble then you might have a different story - it which you need to turn the isolator valve.

Whether you call it an octo or not, you need 2 second stages - usually refered to as primary and backup in this realm instead of octo. With doubles independent or not you also need 2 first stages.

 

[jduncan]

Yes - understand the need for the two first/second stages. My issue was with the existing octo (or secondary) - I would assume it would be removed or I would have THREE second stages.

 

[ianr33]

By removing the octo I mean - Right now we have a 2nd second stage - an "octopus" for lack of a better term, on a yellow hose. With the doubles setup, I wouldn't need this correct?

If the plan is to stay within NDL, then will the doubles count as "backup" gas if they are not isolated? I would assume that having 160 to 200CF of gas on a dive within NDL, you would have plenty of reserve - will this take the place of a "pony tank"?

We thought about a pony rig, but after we spend the cash for the tanks, regs, and rigging, we are almost better off to setup the doubles. I'm afraid after a few dives with pony rigs, we'll wish we just went doubles.

Thanks for the reply!

Jeff

You will have one first stage and one second stage on each tank.You can use the existing "octopus" second stage regulator but will most likely need to change the hose length. (and the colour )

Manifolded doubles are not 100% redundant.It is possible (but very unlikely) to break the manifold on both sides of the isolator valve which will result in a total gas loss.You can cope with most failures if you shut down the correct valve and do it quickly.
If you do not know what you are doing with the valves then you may as well be diving a big single. It is not rocket science but it does need practice.You might want to consider doing an advanced nitrox course which is where you would learn this stuff

 

[Gilldiver]

This may be a bit long, but bear with me.

After 28 years of diving, every time I get asked about doubles I ask back "what do you want to do?" Doubles let you do two things that a single can't- stay longer at shallower depths and go deeper. Both of these bring on DECO problems very quickly. If you are not prepared for DECO, then stay with the singles and NDL diving. If you want some extra gas, a small 20/30/40 bottles as a pony or stage work well.

Now what do you do with the extra gas - most divers will use the gas for exploration of some type be it wrecks, caves, reefs, or photos. At this point the diving has become a tool that lets you do that other thing.

For anyone who wants to go further and get into doubles. I always recomend starting with the old standard aluminum 80's. Why?

Less cost - for your first set of doubles picking up 2 80's used can be done for less then $160 (sometimes much less say $50 each), add a manifold (new 200/used 100) bands (new 65-100/used 50). Total cost 300-350. Or a little over what you might pay for a single steel tank. A new set of tanks, manifold and bands will run at least $750 and can get up to a grand. Also, as you travel around the world you will most likely only find aluminum 80's. So if you plan to travel, get used to using them.

Weight - I think you can figure this part out. Steels on land suck and for boats, it is not getting off that you worry about (gravity will see to that) it is getting back on. A fully riged set of 120's will be a ***** to control on a marginal day and bucking ladder.

Now go diving - a lot.

Is this what you realy want to do? Do you want to put the time and money into it? Will you get bored in 2 years? The sad fact of it is that many, if not most, of the people who post on this board will drop out of the sport in 3 years or less.

OK, if you made the jump to deep/long diving and need more gas then the 80's. Break up the set, the 80's are now called stage bottles, and get the steel tanks you need to do that thing you want to do. The manifold can be reused and maybe the bands.

Now you have a large set of steel tanks, 2 80 stages, and most likely a 20-40 foot small bottle. You now have the tanks to jump 200-250+ feet or go a long way back into a cave- if you want to.

Many will question the 80's because of trim but we can work you through that problem quickly.


Now go diving, - A lot. Play with your rig, adjust the BC/back plate and compensation weights till you get what works for you There is no substitute for experiance.

As for your regs, the posts above go through the standard way of riging them. I might also sugest that you get Y or H valves on your singles and a dedicated BC for the doubles. That way your regs and back plate transfer between the doubles and singles with no changes in configurations.

Finaly have fun.

Pete Johnson

 

[Scared Silly]

Folks have put you on the right track. From the sounds of it you will need the follow to complete the basics of your rig:

2 sets of bands $100
2 Manifolds $170
2 Regs (1st and 2nd stages) $350-$500

Now just to give you the other part if you did go the pony/stage/deco bottle route (I give you this cause once people who go to double adding a deco bottle is next, especially if you do as folks suggest - take a adv. nitrox/deep course). So it might just be a case of which you get first

2 x 40cf Bottles $150
2 x Regs (1st and 2nd stages) $250
2 x Stage bottle rigging $10

Now one comment regs for deco/pony bottles we use Mares MR12s (under $200)which is a nice little reg and is easy to maintain. (Pony/stage/deco rigs get a bit of neglect at times). But for our primary/secondary regs they are both from Atomic (over $400) which are better performers (one of which is on a 5' hose).

So when buying a new reg think about long term. Perhaps the current regs might make fine primary or secondary or deco regs. Then buy accordingly.

Now one thing folks have not touched upon is whether you are diving wet or dry. If you are diving wet using double up steels is not reccommended becuase of being overly negative at depth. In this case using doubled Al is the reccomended route. If you are diving dry then either are fine. A search on this subject will lead to lots of discussion. However, cause you are in the NE I am assuming you are diving dry but wanted you to be aware of this guideline.

 

[Meng_Tze]

I see, so regarldess of whether the tank valve to the first stage is closed or not, gas will be flowing below the vave to the manifold. I don't know this.

By removing the octo I mean - Right now we have a 2nd second stage - an "octopus" for lack of a better term, on a yellow hose. With the doubles setup, I wouldn't need this correct?

If the plan is to stay within NDL, then will the doubles count as "backup" gas if they are not isolated? I would assume that having 160 to 200CF of gas on a dive within NDL, you would have plenty of reserve - will this take the place of a "pony tank"?

We thought about a pony rig, but after we spend the cash for the tanks, regs, and rigging, we are almost better off to setup the doubles. I'm afraid after a few dives with pony rigs, we'll wish we just went doubles.

Thanks for the reply!

Jeff

Yes, the manifold allows gas to go from one tank to the other regardless of valve open/closed. The isolator only prevents gas going from one tank to the other.

Octopus has been answered I believe.

Reserve gas is basically gas you reserve for emergencies. It does not normally state where this gas has to be. I have never heard of any one isolating tanks to have 'backup' gas'. People do not normally dive with the isolator valve closed. This defeats the purpose of a manifold. Independent doubles are separate and would fulfill this need?

You need to see what the operators mean by 'reserve gas'. Most probably it is just having it available. If you have two divers with doubles, each keeps a certain amount of gas in reserve. This can be for yourself, or your buddy. There are many gas rules that can be applied depending on the situation. But always think of this: if your buddy does not have your reserve gas, you need to carry it yourself. Then you need to assess if you need this as part of backgas, or a separate tank. This also depends on what you want to do and how high/low your tolerance for risk is.

I also can not say if you would have enough gas for NDL, that depends on depth, consumption rate (sac, work load, cold, etc, etc). At 130ft gas goes a lot quicker than at 80ft.

 

[ehuber]

"You can use the existing 'octopus' second stage regulator but will most likely need to change the hose length."

Is it advisable to get a true regulator for the left post rather than simply using the existing octopus? Or do most simply buy an extra first stage and just transfer the octopus to the other post without the need to buy the 2nd regulator?

With the cost of bands, manifolds, long hoses, backplate, wing, tanks it would be a way to --at least temporarily-- keep the costs down a bit.

Good questions in this post.