What form of redundant Gas supply is preferred?

[DevonDiver]

If it is a dedicated dive day, and I am not working, then I will opt for doubles. I can sometimes rack up a little deco or will be penetrating wrecks on those dives... so twin ali 80s using rule of 1/3rds.

On working days, I'll sometimes drop in for some photos, in between leading customer dives, or be on a boat with other customers, that will limit my dive time - so I'll just use a single ali 80. On those dives, I'll pretty much be <60ft and <75min dives, just doing macro photography on reef. Clear water, no current and I know the sites like the back of my hand. No need for a full pony cylinder...and I know that I can easily CESA from beyond 18m... so Spare Air is a complete waste of time.

 

[seahorsey]

How magical, here I've decided I GOTTA go solo, and finding out about extra air is the first step - and this is the first thread I see! Listening to you guys feels like coming home. So usefual - thanks to you all! Two extra questions, whaddaya think of the H2Odyssey Extra Air system, H2Odyssey Extra Air System reviews and discounts, H2Odyssey ? And where do I find out more about how to best 'sling' that 19 ft pony I am considering? I assume there are many ways to route hoses and stow regs and guard against shifting....

 

[SelkieDVM]

In the quarry, usually it's manifolded neutral AL80s. In the ocean, single HP100 with slung 30.

 

[Stoo]

It depends on the dives you are doing to a large extent.

Agreed... If I was doing a little putz-about in 50', I would happily dive a single and be comfortable with a free ascent.

Beyond that, I always dive doubles with an isolator. And often a 40' deco bottle to boot. In spite of what I said above, I can't remember the last time I dove solo wearing a single tank. Or a dive shallower than 50'.

 

[sylpha]

If it is a dedicated dive day, and I am not working, then I will opt for doubles. I can sometimes rack up a little deco or will be penetrating wrecks on those dives... so twin ali 80s using rule of 1/3rds.

On working days, I'll sometimes drop in for some photos, in between leading customer dives, or be on a boat with other customers, that will limit my dive time - so I'll just use a single ali 80. On those dives, I'll pretty much be <60ft and <75min dives, just doing macro photography on reef. Clear water, no current and I know the sites like the back of my hand. No need for a full pony cylinder...and I know that I can easily CESA from beyond 18m... so Spare Air is a complete waste of time.

could you please explain american cylinder sizes to me. we use metric sizes usually to 232bar unless stated to 300bar (physical size remains the same). I need to translate that into which size cylinders to use on a trip where they use american sizes. easy enough if you know standard sizes & pressures.

 

[Jax]

How magical, here I've decided I GOTTA go solo, and finding out about extra air is the first step - and this is the first thread I see! Listening to you guys feels like coming home. So usefual - thanks to you all! Two extra questions, whaddaya think of the H2Odyssey Extra Air system, H2Odyssey Extra Air System reviews and discounts, H2Odyssey ? And where do I find out more about how to best 'sling' that 19 ft pony I am considering? I assume there are many ways to route hoses and stow regs and guard against shifting....

My .02psi: I went with slinging a pony because there are many other uses, such as making it a deco bottle.

 

[DevonDiver]

could you please explain american cylinder sizes to me. we use metric sizes usually to 232bar unless stated to 300bar (physical size remains the same). I need to translate that into which size cylinders to use on a trip where they use american sizes. easy enough if you know standard sizes & pressures.

Sure mate....am a Brit also. Just been living abroad for too long

AL80 = slightly smaller than 12l. More detailed explaination below, courtesy of wikianswers....



There is a fundamental difference in the system of measure of a cylinder in Europe and the USA.

Europe: Absolute interior volume in liters. You can think of this as how much water could be used to fill a tank (if this was used in the USA you could think of it as a X gallon tank)

USA: Gas in the tank at the tanks rated pressure. This is why when you convert 80cu FT to liters you get some bizarre number that doesn't seem accurate based on what we know of American Cylinder markings. (80 cuft = 2265 liters)

The most common question when it comes to tank size in the USA:

80 cuft at 3000 psi can be represented as:
80 cf/ 201.34 atm = 0.397 cf (or cf/atm)
0.397cf x 28.32 l/cf= 11.25 liters

12L tank at 3000 psi can be represented as:
12L / 28.32 = 0.4237
0.4237 * 201.34 = 85.31 cuft

12L is approximately an 85 at 3000psi. but... working pressure is 200 bar or 2900 psi... so the actual US equivalent is actually "smaller." above the 201.34 represents atmospheres... which is the metric unit "BAR"

so:
200bar * .4237 = 84.74 Cu FT

A standard European 12L scuba tank is US equivalent 84.74 Cu FT

Or simply:

(X Liters / liters per cu ft aka 28.32) * atmopheres aka BAR = Us tank cuft markings


Here is a table borrowed from another thread:

10 litre = 0.353 cf
2250psi tank... 54cf
3000psi tank... 72 cf
3300psi tank... 78 cf
3500psi tank... 83 cf

12 litre = 0.424 cf
2250psi tank... 64 cf
3000psi tank... 86 cf
3300psi tank... 94 cf
3500psi tank... 100cf


15 litre = 0.530 cf
2250psi tank... 80 cf
3000psi tank... 107 cf
3300psi tank... 18 cf
3500psi tank... 125 cf


20 litre = 0.706 cf
2250psi tank... 109 cf
3000psi tank... 143 cf
3300psi tank... 157 cf
3500psi tank... 167 cf

A simple explanation is 80cubic feet of air is 2265 litres at atmospheric pressure it is compressed to fit into a 12 litre tank by increasing the pressure to 3000 psi

 

[Dive-aholic]

How magical, here I've decided I GOTTA go solo, and finding out about extra air is the first step - and this is the first thread I see! Listening to you guys feels like coming home. So usefual - thanks to you all! Two extra questions, whaddaya think of the H2Odyssey Extra Air system, H2Odyssey Extra Air System reviews and discounts, H2Odyssey ? And where do I find out more about how to best 'sling' that 19 ft pony I am considering? I assume there are many ways to route hoses and stow regs and guard against shifting....

I wouldn't bother with a system like that, especially considering where it mounts. How easy do you think it will be to deploy that system in a real emergency. Slinging a pony in front of you is a much quicker option, as well as more versatile. Get a 40 and you'll have your deco tank for future training.

(good choice, Jax!)

 

[FritzCat66]

15 litre = 0.530 cf
2250psi tank... 80 cf
3000psi tank... 107 cf
3300psi tank... 18 cf
3500psi tank... 125 cf

Something amiss here - 3300psi = 118cf perhaps?

 

[seahorsey]

Thanks! What do you recommend I sling it with? Preferred methods of securing it, mistakes or gear to avoid?