Bail out cylinders are people using.

YobazEfendi said:
If a containeris neutral when empty, it is not possible to put some thing in to it and make it float.

Unless you stretch the boundaries.


What you mean might be that 50 bars of air is heavier than 260 bars of trimix?
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So how does a helium baloon work?

But thats nto the point.

It wont suport the reg and first stage but it floats arse in the air, like an AL 80 with 160 bar in it does.


Rear view in fresh water (obviously floats up more in salt water.)

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Steel 10 100bar 80% Salt water

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Steel 7 with 70bar 32% on left full 7 on the right 250bar 50% Fresh water

seetheyfloat3.jpg



Steel 7 100 bar

floatingtanks.jpg
 
With a balloon you are stretching the boundaries and the air lifts it.


An empty scuba tank with 0 bars will be lighter rhan a scuba tank with 1000bars of helium in it.


But I understood your point.


If you like the steels so much why not strap a bit of foam on to it?
 
Helium ballon worjs just like your wing or your bc. Its weight/volume is less than the weight/volume of the surrounding medium. So it is pushed up.
 
YobazEfendi said:
With a balloon you are stretching the boundaries and the air lifts it.


An empty scuba tank with 0 bars will be lighter rhan a scuba tank with 1000bars of helium in it.


But I understood your point.


If you like the steels so much why not strap a bit of foam on to it?
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WHAT and look un cool :D


I dont like any tank in particular. I just find one steel with He + 1 Al80 with nitrox in trims out well left right.


If it worked with two steel or two 80s id do that. But is dosent.

I own both.


Here you go

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Steel 10 250 bar 18/45
IMG_3887.jpg


Al80 a bit light with only 210 bar in
IMG_3888.jpg


Fresh water

Full 80 riged to dive 5lb negative with 50% in

IMG_3890.jpg



Full steel 10 with 18/45 6lb neg
IMG_3889.jpg



Steel 7 with 260bar 50% in 6lb neg
IMG_3891.jpg
 
sdryan11b said:
Is anybody carrying steel tanks like maybe 85s or 72s for a little extra weight
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I use aluminum 72s for bailout when saltwater diving and for stage and/or bailout on deeper/farther cave dives. AL 80s work too, but they're not as nice.

I like two LP steel 85s with a cave fill for long duration cave dives or cave dives using a scooter and only 2 bailout/stages. I get about 250 cu ft of gas in them with the cave fill and I like the buoyancy characteristics when cave diving, using the scooter, don't want 3-4 tanks.
 
For my type of diving for bail-out I use:

N32 2 x 18 ltr. steel side-mount
N32 2 x Alu 80 under-mount (usually to be staged)

The rebreather has 2 x 3 lts. steel O2 de-inverted bottles (I use N32 as diluent from the bail-outs).

bailout.jpg
 
Why only EAN32.

Please do send pictures of your 2x18 setup. I am very interested as my friend has ome for sale. I was considering buying them but thought they were unpractical.
 
Come to think of it. It looks like you are cave diving. So you are not realy using them for deco.

How do they trim out? And what are your plans if you have to use them? On those 2x18 you have 7200l of gas (if at 200 bars) or 9000l if at 250. Which makes about 11 kg of gas.


Flood rebreather? Dumping steel tanks will not help.
 
YobazEfendi said:
Flood rebreather? Dumping steel tanks will not help.
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You aren't thinking outside of the box. :brickwall

You dump the rebreather and exit on OC. I have my rebreather setup to ditch it in the event (though unlikely) of a catastrophic flood. It's a $10k piece of equipment or your life, that is how I look at it.
 
I am pretty sure most rebreathers are heavier when they are flooded.
Tahn no rebreather at all.

If you are swimming comfortably with 10kg of gas. You need to lose some buoyancy when you start to vent that gas after using it.
 
Dont get me wrong. I am typing from a mobile device and my sentences are short. I am only asking questions and trying to find out. No criticism whatsoever...
 
I started cave diving using what was an "optimal" configuration for 100 meter sea diving, and realised that in caves it did not work.

So, I had to get back to the drawing board, and figured out a configuration which worked for me in caves for the type of diving which I am doing.

I like to dive 2 - 3 hours exploring various parts of the cave and do this as a "self-sufficient" diver - which means carrying into and out of the cave the equipment on my own and using it on my own.

For the working part of the dive (which in a cave is most or a good portion of the dive, other than for very "deep" caves) I do not want to exceed a desired loop pPO2 of 1.0 (which allowing for a 20% error/lag in the sensors and the electronics means an actual range in use of between 0.8 and 1.2 pPO2).

So, the above explains configuration and choice of gas.

Because it works in a cave, it will also work at sea (the cave generally being a more complex environment than the sea).

The set-up from a risk management stand-point is modular. This means that the rebreather is ditcheable/removable (using Spinnaker Sheet quick-release dinghy shackles) and the system has to be operational with or without a rebreather on the back.

The advantage is if when I fire up my rebreather in the garage or the dive site and it does not work, I leave it behind and happily go diving. Diving, I have the option of keeping the rebreather or ditching it depending on the circumstances (i.e. restriction, flooding...). Of course it can also be flooded in extreme circumstances as a last resort to reduce buoyancy, but this would only add max. Kg. 5 of weight/negative buoyancy (which I can generally add by other means if I am too light).

The one thing I do not want to end-up with is a lot of lead, but no gas (no gas I cannot fix, everything else I can fix/manage).

So, as to buoyancy and trim:

1. The rebreather taken in isolation (intact without flooding it) ranges from negative to slightly positive and this is managed by loop volume alone.
2. The side-mount 18 liter steel tanks each range from negative buoyancy of Kg. -4.34 when full to a positive buoyancy of Kg. +0.66 when empty (excluding tank valve and regulator using Air for the calculations).
3. The Alu 80 each range from negative buoyancy of Kg. -0.1 when full to a positive buoyancy of Kg. +2.65 when empty (excluding tank valve and regulator using Air for the calculations).

With dry-suit and a small wing, the modularity of the system (you can add/remove/ditch the system components "on-the-fly") gives me a number of options.

Looking at the most basic situation, which is the rebreather cannot/should not be used and is left home (or ditched), I can happily dive with no weights and no backplate (I do not use a backplate on the rebreather either) OC exiting the cave with 50% gas in the tanks (18 liter steel side-mount). I have exited the cave with 70 bar in the tanks each no problem (any less I'll be too light, but I'd rather be too light with a lot of gas left, then "just right" with no gas... "too light" is easy to fix, "no gas" I cannot fix).

As to trim, if you normally use Kg. 8 to 10 of weights and Alu 80s, by using the 18 liter steel in place of the Alu 80 and with no weights, you are obtaining the required negative buoyancy from the choice of tanks, and the negative buoyancy (the weight from the tank material/shape) is distributed evenly along the two sides of your body (rather than being concentrated on lead weights wherever you place them).

Choice of undergarment in the dry-suit is also important. I use an Arctic 200 against the skin (no thermals or other bits to carry wear/wash/forget...).

That works for me based on the diving I do and the way I do it and my body shape and buoyancy characteristics.

From a buoyancy stand-point, steel is superior to aluminium for side-mounting for me, and the 18 ltrs. have better characteristics than the 20 liters or the 12 or 15 liters.

For staging, and passing tanks to a buddy, Alu 80s are superior to steel from a buoyancy perspective (for me).

Hope this answers all questions... but to summarise for the noob who started the thread and asked the question:

1. You need "a lot of gas" for bail-out.
2. "Not enough lead" is better than "not enough gas."
3. What works for you (in the environment you dive and in the way you dive and the way you are), is what is good for you.
 
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I use Faber 18 liter steel.

The rated pressure is 220 bar at 15C.

I fill them to 232 bar at ambient temperature (since 10C temperature change gives me 10 bar pressure change roughly... but I am sure more mathematically oriented forum members will correct me).

Now, that is on day 1 of the dive.

On day 3 of diving (since I leave the steel tanks in the cave), the left tank will be at 180 bar (used as diluent + wing inflation), and the right tank at 220 bar (used for dry-suit inflation).

The Alu 80s will be full and staged in the cave.

Typically at that point I refill the left 18 liter steel.

The whole history (pictures) of my configuration from sea to cave is in my forum under the "My Meg" topic.

You can see briefly the concept clicking this video link here:

Europe 2012 Part Two - YouTube

In the video the configuration is wrong. The side-mount tank on the right should be on the left (which means the 1st stage and HP hose/gauge should then be facing up and not down).

The LP hoses should not be loose, but run under the counterlung (or the counterlung retaining strap which stays with the harness when the rebreather is removed).

The dangling electronics on the right should not be there. Basically, one was a test CO2 Monitor 1 ATA box which is now gone, and the other is the Meg Primary display whose cable has to be tucked under the counterlung (or the counterlung retaining strap which stays with the harness when the rebreather is removed) to stop it from dangling loose.

...there is more room for improvements of course (it is always "work-in-progress") and any criticism suggestions is most welcome.

Hope this helps to understand the system.
 
Red Sea Explorer said:
i think you guys are over thinking this..... I just grab whatever is on deck and go diving..... :-)
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The degree of "thinking" required depends on the complexity of the dive and the environment of the dive.

If you are doing an Open Water MOD 1 dive to 20 meters, then you could use a 3ltr. aluminum tank as bail-out (in addition to your inboard diluent), but then you would also be carrying a lot of weight (lead).

By judiciously choosing cylinder capacity and material for more complex dives and environment you can maximise gas carried, minimise bulk/drag, reduce lead.

I dive with no lead weights or backplate, for example.

A MOD 1 diver with dry-suit may dive with as much as Kg. 12 of lead weights initially.
 
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