Going doubles - questions

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Well it depends if your "octopus" is one of those hockey puck yeah I'm sort of a second stage type devices I would get a new second stage. If like mine its just another second stage albiet maybe not as expensive as my primary I'd stay with it.
 
This can´t be a short post, sorry!

Originally Posted by Gilldiver
Every time I get asked about doubles I ask back "what do you want to do?
This is, IMO, a VERY important question. All the answers given above are based on an assumtion of what you want to do. Take the time to think about what you want to do now and what you think you want to do in a year or two.

The fact that charters require redundant gas for the dives you want to do makes me assume that you´ll either be doing "extended range" dives or skirting the edges of them, I´ll frame my advice accordingly.

As you already have 2 pairs of singles (and both you and your buddy are comfortable with the idea of doubling them), I´d say go ahead.

It is possible to dive doubles without a manifold (independent) or with the manifold closed (essentially independents with additional failiure modes) but I´d advice against it. If you decide to get a manifold, which is what I´d recommend, absolutely requires you to become proficient at opening/closing your valves in a "correct sequence" (opinions vary as to what this is), a failiure of the manifold could still lead to a loss of all gas which is why I´d recommend a longhose and a "commited buddy" (as your buddy is then your "redundant airsource" in the rare event of such a catastrophic failiure).

Personally I´d get a second set of the same 1st stage and "primary" that you already have together with a long hose (this means retiring your current octo to a "spare part"), the identical set for ease of maintenance, better performance and spare parts. A longhose because I believe that if practiced and use "correctly", it will make dealing with OOA´s and other airshares easier and more comfortable, particularly since I gather that you will be diving regularly with the same buddy.

I don´t have a Cobra but if it has "download capability (like my Vyper), you can easily adjust tankvolume in SDM, regardless gasmanagement is something you should get serious about (lamonts "treatice" is a great way to get you asking the right questions), beyond following your Cobra or "coming up with 50 bars left". Especially since you (assuming you go with the 2 different sizes of tanks) need to do "gasmatching". I´m not saying you don´t know about all of this, I´d just feel remiss if I didn´t point it out...

Once you manifold your tanks, they´re best left manifolded. Either dive doubles all the time or get an extra single for those dives would be my advice (this is what I´ve done)...

Originally Posted by Meng_Tze
Right post is primary reg and inflator hose. Left post is backup reg, optional drysuit inflator and spg.
I´d say that this is the most common way to rig your hoses...

YMMV
 
If you are confident that your octopus will work at 130 feet in a stressful air share situation keep it. If you have any doubt if it is good enough or not replace it.
 
Thanks everyone.

As for what we are going to be doing - That is clear in my original post - We are looking to have enough gas to do some deep diving to 130 feet, within NDL, and have enough reserve gas to surface with safety stops if one buddy has an OOA situation at depth. We'll also likely be using EAN 28%.

In a year, we may move toward taking the advanced nitrox/deco classes.

So that sums up what we want to do.

I think I have decided that we are going to get the PST E7 HP80 tanks for doubles. They are cheaper than using our fabers, and it will allow us to keep the four fabers we have for single tank dives. Plus the E7's are lighter.

We will be drysuit diving with these.

We'll get another set of GS200 regs to match the current ones.
We'll get OMS 8" tank bands
We'll get OMS 45 pound lift bungee wings (enough lift?)
Well get OMS 300 BAR Rotation crossbar manifolds

How long should the hose be on the new second stages?

Anything else I've missed here?

Thanks again.

Jeff
 
What is the NDL at 130ft for 28%? I dont have the NDL tables..should be what 15 mins (I am guessing here) or so? With that takes maybe 2 mins to go down. So you have 13 minutes at the bottom and then go back up to stay in NDL. All this extra cost and effort for 13 minutes on the wreck.

I am not saying dont do it, I am just pointing out that doubles is one side of the equation, the other is to be able to use the right gasses.... You indicated to do that so I think you are on the right path there
 
jduncan:
Thanks everyone.

As for what we are going to be doing - That is clear in my original post - We are looking to have enough gas to do some deep diving to 130 feet, within NDL, and have enough reserve gas to surface with safety stops if one buddy has an OOA situation at depth. We'll also likely be using EAN 28%.

In a year, we may move toward taking the advanced nitrox/deco classes.

So that sums up what we want to do.

I think I have decided that we are going to get the PST E7 HP80 tanks for doubles. They are cheaper than using our fabers, and it will allow us to keep the four fabers we have for single tank dives. Plus the E7's are lighter.

We will be drysuit diving with these.

We'll get another set of GS200 regs to match the current ones.
We'll get OMS 8" tank bands
We'll get OMS 45 pound lift bungee wings (enough lift?)
Well get OMS 300 BAR Rotation crossbar manifolds

How long should the hose be on the new second stages?

Anything else I've missed here?

Thanks again.

Jeff
Are 80cft going to be enough for you going forward? Most people when they go on the path of different gasses, find that 80cft doesn't last as long as you are able to go. Steel tanks are not generally used as stages because of buoyancy characteristics. AL80's are.

I.O.W. think ahead of the curve, in a year/two years time would you w still be happy with 80's? If you think so, thats good. If not, can you sell your HP80's easily? If so, good. If the answer is 'no' or 'not sure' on either one... rethink and make a decision.

45# sounds like it is enough (look at all your equipment and the tanks full).

Second stage hoses usually are 22" (or was it 24"?) for backup and 5-7ft for primary. Get someone who has a set up to help set up the rig, it is not something that you will get down in detail on the internet. Also learn to dive and manage the hoses.
 
Jeff,
If your heading down the road to tech I would not bother with the 80's. Go right for the 120's or 130's. This is good for tech diving and also works good for 2 tank rec dives.
Pat B
 
Twin 130's is a hell of a lot of gas for a recreational dive.Heavy as well
You could use a single 130 for now with an H valve and double them up later if you wish. That would give you the redundancy of doubles except for tank O ring or burst disc failure.

In your situation I would go with the twin Al 80's

As always too many choices !
 
At 1.5 PO2 and EAN 29% (max depth 132) my Cobra shows about 10 minutes bottom time at 130 feet. This would be the worst case, as many dives are not that deep. Again, we are just trying to have enough reserve gas for some deeper dives

If the 80's are not enough at some point, we have a pair of Steel Faber HP 100's. We can always get another set of those.

Matt Silvia has volunteered to assist with the setup, which is ver nice. Hopefully, we'll have one put together by the weekend.
 

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