Small Double's Kit

[Scubabill]

Here is my configuration I would use if I were to step out of the envelope. Triple 40's one mounted upside down with the valve at the right hip. All connected by 1/4" stainless tubing and fitting. The valves would have to be drilled and threaded to accept the SS tube fittings. 80 cu/ft with 40 cu/ft kept isolated. Run the first two empty, open the third and call the dive. You could still stand the rig up right on two cylinders.

Sounds like a nice kit for sure, and the cool factor is off the charts. But a little more weight then i want back there. for my shore diving i might hit currents on some days. So if i design this rig to be comfortable, i wont mind hiking back to the lot as much!
W/3 im adding about 20 lbs more. And i don't think i need that much redundancy diving
in under 50ft. If going deeper ill just sling on a 20 and be good to go. But triple 40s
would be some abyss looking stuff, with SS lines, and polished back plate, with high quality bands and hardware, no doubt about that!
Thanks

 

[DaleC]

I'm curious about your thinking regarding redundancy.

If you use twin 45cuft tanks and breath one down to 500psi you wind up with about 8.5cuft in reserve. With twin 40cuft tanks about 6cuft. This takes into account a loss of gas on the cylinder you are breathing after the switch.

Seems like a lot of trouble and expense to (in effect) carry a spare air.

Not trying to be negative but is all the trouble worth it for so little reserve gas (and the false sense of security it will give you) in a situation where you don't really need redundancy anyways? Twin the small tanks if that's what you want (variety is the spice of life) but practically speaking you would be better off doing proper gas planning using a single tank and being well versed in CESA's from that depth. If you try to do deeper dives with that rig as you say by slinging a pony/stage you will have a real problem keeping on top of the rapid depletion of gas. Twin small bottles will be more of a hazard than anything and you will also need 3 sets of regs to do the job of two.

With regards to the upsidedown valves. If you are diving independant twins you really have no need to manipulate the valves during the dive. That's the benefit to that set up.

Again, not knocking your ideas outright, just offering a counterpoint to consider.

 

[Scubabill]

I'm curious about your thinking regarding redundancy.

If you use twin 45cuft tanks and breath one down to 500psi you wind up with about 8.5cuft in reserve. With twin 40cuft tanks about 6cuft. This takes into account a loss of gas on the cylinder you are breathing after the switch.

Seems like a lot of trouble and expense to (in effect) carry a spare air.

Not trying to be negative but is all the trouble worth it for so little reserve gas (and the false sense of security it will give you) in a situation where you don't really need redundancy anyways? Twin the small tanks if that's what you want (variety is the spice of life) but practically speaking you would be better off doing proper gas planning using a single tank and being well versed in CESA's from that depth. If you try to do deeper dives with that rig as you say by slinging a pony/stage you will have a real problem keeping on top of the rapid depletion of gas. Twin small bottles will be more of a hazard than anything and you will also need 3 sets of regs to do the job of two.

With regards to the upsidedown valves. If you are diving independant twins you really have no need to manipulate the valves during the dive. That's the benefit to that set up.

Again, not knocking your ideas outright, just offering a counterpoint to consider.

Well i'm kinda shopping for ideas at this point.
But i do think dual tanks are safer. If i dive solo in 50Ft, on a steel 80 and i get a bad free flow or total loss of air, nothing i can really do at that point but swim the rig on a breath hold. With the twins i can just turn off the free flow tank and abort the dive safe on air. Now how to route this kit i'm still stuck on. independents vs manifold....
Prob. leaning towards independents right now. If i can run dual tanks independent,
that will give me dual regs. I also would like to find a company/person that would be willing to help me build a dual bladder wing in the 20-25 lb range. Im also researching ways to be able to cut flow to the inflator in case of a free flow failure, and still be able to use the air out of that tank to surface.
So with a light weight rig like this, i can if possiable, isolate an entire side of the system if there is a problem. and have enough air to surface safe. Even if a problem happens with one tank at 500psi, and the other at 500psi, that gives me plenty of air to surface safe and controlled. If im diving deeper then say 60 or so feet with a buddy,
i would just carry a sling 13 tank or so.....
I feel without doubt im technical enough in nature to dive this rig safe. I have enough
since i feel to watch the gauges, and switch over when needed, on time ect ect.
So thats kinda were im at now. But learning more every miniute, and this all could change soon.

 

[AndyNZ]

. If i dive solo in 50Ft, on a steel 80 and i get a bad free flow or total loss of air, nothing i can really do at that point but swim the rig on a breath hold.

Do you want to re-think that? I read this as you are intending to swim to the surface holding your breath.

Now how to route this kit i'm still stuck on. independents vs manifold....
Prob. leaning towards independents right now. If i can run dual tanks independent,
that will give me dual regs.

Indpendents come with more problematica gas management issues - but then at 50' you'll probably not use too much from any one tank, if you are using say 10L tanks.

You also don't necessarily need the true redundancy of manifolded twins. At 50', the chances of you needing to access your entire gas supply (e.g. to complete deco) is pretty much irrelevant.

In fact, you're better off probably with a large single tank and a pony bottle that you carry as slung tank.

I also would like to find a company/person that would be willing to help me build a dual bladder wing in the 20-25 lb range.

If you have that much money that you really want this, if you want to pay my flight and costs I'll come over and do some training for you.

You are over-complicating this. Ask yourself, why do you need a dual bladder?

You simply don't.

Im also researching ways to be able to cut flow to the inflator in case of a free flow failure, and still be able to use the air out of that tank to surface.

It's called a manifold. Even better, be neutrally buoyant at all times - who cares whether you have to isolate gas supply to your wing? You simply swim up, air int he wing expands, makes you positively buoyant, vent air as you ascent to control your ascent rate. Rocket science??

So with a light weight rig like this, i can if possiable, isolate an entire side of the system if there is a problem. and have enough air to surface safe.

At 50', what sort of problems are realistically likely that will cause you any real problems at all?

Even if a problem happens with one tank at 500psi, and the other at 500psi, that gives me plenty of air to surface safe and controlled. If im diving deeper then say 60 or so feet with a buddy,
i would just carry a sling 13 tank or so.....

So now you've got indpendent twin 40 cu ft and a slung 13 cu ft? What's the point?

I feel without doubt im technical enough in nature to dive this rig safe.

Maybe you feel that..... others may be sceptical.

 

[DaleC]

Scubabill,

To aid the discussion perhaps you could tell us what region of the world you will be diving. This has a bearing on the (best) type of rig you would use.

Many of the things you are talking about have been done and discussed. Use the search function here on SB for the following research to see how they work and why/when they are used:

Dual bladders pros vs cons.
Manifolds vs independant doubles pros vs cons.
Hose routing for manifolded and independant doubles.

With regards to having enough air to surface safely from less than 50'. You will have enough even in the event of a large gas loss even with a single cylinder. You can either continue to breath off of a free flow to the surface or do a straightforward CESA. Because you are less than 50' and gas limited as to NDL's (by your small tanks) you could bypass the safety stop with little risk if need be.

Redundancy really comes into play when you go below 50-60' or if you dive in locations where direct surfacing is not an option (diving near boat traffic, surface currents). Below 50-60' you are pushing your abilities to safely CESA and/or you are incurring enough of a deco obligation (even within the NDL) to make a direct ascent less desirable (hence redundancy).

Some people think redundancy is there to allow added gas to solve problems at depth. Not really. This type of reserve should be accounted for by using the appropriate size of main tank to allow for usable and reserve volumes. If you have a problem at depth you should be able to solve it off of your back gas (problem one). Redundancy is there if you lose your back gas (problem two). Generally speaking one plans to cope with problem one or problem two but not both at the same time.

When you consider safety you need to balance the risk of diving one larger cylinder (no redundancy at shallow depth) vs the risk of regulator switches to ensure adequate gas supply (redundancy at shallow depths). There is a greater risk that you will accidentally blow the gas management of small independant twins and either go OOA on a cylinder or breath it past a usable reserve.

Nothing disturbs me about your shallow diving plans (just offering counterpoints) as I like to tinker with my rig as well. Build away I say. Your thoughts on taking it deeper do worry me though. Diving with three small independant tanks below 60 ft is a recipe for disaster and I don't think anyone (with sense) will recommend it. If it's the "ultimate" shallow rig, keep it shallow. If you want to dive deep build another "ultimate" deep rig... or dive a simple HOG rig which is the ultimate for all around Rec/Tech/Shallow/Deep/Minimal/Monkey diving.

 

[Jimmer]

Double 72's on the left, double 45's on the right. I also own a set of double 130's that are for my tech training, but these 2 sets are the ones that end up on my back more often then not. The 45's are nice light, well balanced, hold a good amount of gas for a rec profile, offer redundancy in regulators in cold water (I dont consider them to offer redundant gas, as the volume of one tank when isolated can leave a lot to be desired if you have been down a while and have 60 or 70 feet above your head). Honestly, they aren't minimalist, they are just plain fun and different, and that is how I view mine. If I wanted true minimalist, I would be diving a single tank like Nemrod has suggested.

Jim

 

[WD8CDH]

Hi Scubabill,

I think you are on the right track with small multiple tanks but I would recommend staying away from independent doubles. I prefer a shorter manifold that places the tanks closer together than a regular manifold. One thing that you haven't looked at is triples with two tanks manifolded and the third tank independent.

I so much prefer small multiple tanks over large singles, that I sold almost all of my singles. The balance and maneuverability is much better than larger singles. I mostly dive triple 30s, Double and triple 35s, double and triple 40s for both shallow and moderate depths.

I don't like inverted tanks unless they are in a housing or have some other method of protecting the valves.

 

[Druid]

One of my buddies dives inverted, manifolded twin 7ltr cylinders, which seem to be the sort of size you are considering. (I don't really understand the US system for measuring tank capacity, but an AL80 is 12 ltrs, so a 7ltr is 45-50 cu ft). He uses them on a Buddy Tekwing bc, but a s/s or aluminium backplate and a small wing would be a simpler solution. He uses a home made valve protector so that the rig will stand up without damage to the valves, I don't have any pictures of his but something like this

should be easy enough to make up. Click here for more info

The only other problem is getting hoses made up to the correct length.

 

[Paladin]

This is a bit off topic but this discussion reminds me of an odd setup I saw once many moons ago. I saw it parked on a dock with some other gear waiting to be loaded onto a big commercial work boat. It wasn't light by any stretch of the imagination, though, just odd. It consisted of three steel 72s with two mounted in the standard double style and the third mounted between those in a sort of pyramid configuration. The diver was using a US Divers Aquamaster mounted on the doubles with a single hose of some kind on the third. He was a pro diver who worked on underwater construction projects. That was the first, and last, time I ever saw such a rig. Anyone else ever see such a thing?

 

[micklock]

This is a bit off topic but this discussion reminds me of an odd setup I saw once many moons ago. I saw it parked on a dock with some other gear waiting to be loaded onto a big commercial work boat. It wasn't light by any stretch of the imagination, though, just odd. It consisted of three steel 72s with two mounted in the standard double style and the third mounted between those in a sort of pyramid configuration. The diver was using a US Divers Aquamaster mounted on the doubles with a single hose of some kind on the third. He was a pro diver who worked on underwater construction projects. That was the first, and last, time I ever saw such a rig. Anyone else ever see such a thing?

SETUPS