Considering small doubles (~50's)

[CT-Rich]

If you are diving independent twins, your pint about the available gas would be correct. A manifolded twinset is no different in terms of available gas as a single cylinder with equal capacity.

My understanding was that he wanted the twins so he could do away with the pony bottle. that would mean he would use two regs to provide the redundancy for solo diving. Personally I, like the trim I get from steel tanks. I always feel diving AL makes my aft too bouant at the end of the dive. I would agree that for smaller divers twin fifties are prefereable than a single 100. of course the women I know that use them can sip that much air forever and make a second dive before getting a fresh fill.

 

[Nemrod]

What does that have to do with anything? The OP asked for advice on the appropriate equipment configuration for his style of diving, which is mostly solo. If you are happy to dive to 60 feet without a redundant gas source, you go for it. Just because you have got away with it for so long does not make it safe.

Like I said, some of us have not just gotten away with it, we have a method which you simply do not understand and we know what we are doing, we will not take direction from a newbie. Did not grow up in your airbag and helmet padded world, I rely on skill and fitness and knowledge, you can rely on layers of equipment.

But read line three in my sig, it applies here. But thanks for your concern.

N

 

[halocline]

If you're going to go for small doubles, I agree that 72s are the way to go. They're cheap and they'll be way more versatile than smaller doubles. You probably would do best to get a standard backplate; the freedom plate (at least mine) is not good for double tanks. A cheap AL plate will be very easy to find. You'll also need a bigger wing, (I almost typed 'wang' by mistake, hehe) unless your single tank wing is already way too big.

You're not really simplifying anything, though, over a single tank with a slung pony. Maybe consider a bigger bailout bottle, like a 30 or 40, which then still gives you true redundancy. The idea of trading a small pony for an even smaller one is stupid; it does nothing except make the bottle less useful. You still have an extra bottle with an extra regulator, it's not any less complicated or noticeably cumbersome. It just means you're carrying something that's not useful except in very specific hypothetical situations.

Regarding the training discussion, it is absolutely true that if you are diving solo in more challenging environments that are making you want redundant air, that's an indication that you have seriously increased the riskiness of your diving. Just getting the redundant air does not make that diving any less risky; many, many dive accident victims are found with plenty of air. So consider all the other aspects; navigation, entanglement, sudden illness, etc....and consider getting trained in solo diving by an excellent instructor. Everyone has his/her own risk tolerance, but I believe that many people fool themselves thinking that carrying redundant air takes all the risk out of solo diving. I'm not accusing you personally of that, I just think it does frequently happen.

 

[DaleC]

For more gas and redundancy a single/pony can also work, to a point.

I reserve 20cuft at 100' for reserve (unless otherwise indicated). If I use a 40cuft pony this allows me to use 20cuft from it for the dive (I usually do this at the beginning and then switch to back gas). With a 100 that gives 120cuft for the dive and 20 reserve.

The only caveat is that you need to make sure 20cuft will fill your ascent requirements after using 120cuft at depth.


As to not using redundancy for some shallow dives. There is no reasonable single mechanical failure that will stop a competent diver from reaching the surface directly. Some divers incorporate this option into their dive training/planning intentionally. This only changes if one is doing an extraordinarily long dive or if there is some sort of ceiling (like boat traffic or kelp) that prevents ascent.

 

[Mustard Dave]

Like I said, some of us have not just gotten away with it, we have a method which you simply do not understand and we know what we are doing, we will not take direction from a newbie. Did not grow up in your airbag and helmet padded world, I rely on skill and fitness and knowledge, you can rely on layers of equipment.

But read line three in my sig, it applies here. But thanks for your concern.

N

My only concern is for the OP, who has asked for advice on a suitable rig for solo diving. My opinion, and that of every agency I know of that teaches solo diving techniques, is that a redundant gas supply is an important requirement. If you are happy diving with the sort of kit that they use decorate the walls with in the cafe at my local dive centre, by all means carry on - I won't try to stop you.

Please refrain from your patronising twaddle. I couldn't give a rat's arse how long you've been diving or how long you think I have. I dive a Hog-rigged set-up, which is widely considered to be a no-nonsense, effective equipment configuration. I hardly think an extra first stage and a manifold would be considered to be 'layers of equipment'. I don't know (or care) how high you value your life but the £130 it cost me to buy another first stage isn't something I begrudge paying to know I have another source of gas in the event of a failure of my primary.

Oh, and my car does not have an airbag by the way!

 

[undrwater]

I DO appreciate the concern and advice from all. It looks as if I will get a chance to touch that set of small doubles mentioned earlier.

As to gas planning, management, and safety; I am always on the lookout for unconscious incompetence, and have plenty of support for further training / mentorship.

Thank you all. I'll post back if and when I've made a decision. Feel free to add anything we might have missed.

thanks again!

 

[DaleC]

My opinion, and that of every agency I know of that teaches solo diving techniques, is that a redundant gas supply is an important requirement.

My take, is that agencies base their ideas on having read R. Von Maiers book once and just copying what he said. Some of those same agencies teach 1/3's for OW diving as well - a concept of conservatism taken directly from cave diving.

Personal comments aside, vintage equipment diving entails a system taken from a time when most divers had no redundant cylinders and used J valves and wrist watches for reserve. There is a cornucopia of techniques to make that sort of diving practical that has been lost in modern dive training.

Not saying modern training is bad; just saying there is more in heaven and earth than can be dreamed of in it's philosophy. A little time spent exploring some of those options can only increase the breadth of a divers knowledge base.

 

[Hatul]

It depends upon what you mean by "ascend safely". If you take what DD stated literally, (100 to 0) you should need between 4 cu ft (@.5SAC) to 6 cu ft (@.75 SAC) to get directly to the surface at 30FPM. If you mean is it enough to execute a standard ascent profile, including a minute to work stuff out at depth, a stressed breathing rate, a deep stop, a safety stop and an allowance for a short fill, then you can double to triple that number.

My SAC here in S Cal diving is approx 0.7 cu ft/min , mildly stressed it's 1cu ft/min so that's what I'll use, forgetting time to sort out problem.

from 100 ft it takes 100/30= 3.33 mins of ascent time which uses (50/33+1) * 1cu ft/min * 3.33 min= 8.4 cu ft
Safety stop takes (15/33+1)*1cu ft/min *3min = 4.4 cu ft

so that gives 8.4+4.4=12.8 cu ft as a minimum. It would require sucking out a 13 bottle empty, and as you point out we often start with partial fills. You also may be more than mildly stressed and require several seconds to get yourself together, so more realistic pony for those depths is a 19.
Personally when solo I use a 13 for depths up to 60 ft or so and 19 for deeper dives.

I was surprised Dumpster would recommend a 6 as usually he gives good advice.

 

[CT-Rich]

I agree with Hatul, a 6 is awefully small for a pony, a step up from a spare air. Unless you are very petit with a really low SAC Iwouldn't invest in something that small. Best general purpose investment would be a 19. I always think of as a 6 as the what you might want for argon in your drysuit.

 

[GrumpyOldGuy]

My SAC here in S Cal diving is approx 0.7 cu ft/min , mildly stressed it's 1cu ft/min so that's what I'll use, forgetting time to sort out problem.

from 100 ft it takes 100/30= 3.33 mins of ascent time which uses (50/33+1) * 1cu ft/min * 3.33 min= 8.4 cu ft
Safety stop takes (15/33+1)*1cu ft/min *3min = 4.4 cu ft

so that gives 8.4+4.4=12.8 cu ft as a minimum. It would require sucking out a 13 bottle empty, and as you point out we often start with partial fills. You also may be more than mildly stressed and require several seconds to get yourself together, so more realistic pony for those depths is a 19.
Personally when solo I use a 13 for depths up to 60 ft or so and 19 for deeper dives.

I was surprised Dumpster would recommend a 6 as usually he gives good advice.

Well, there are 3 differences between your calculations and mine. I can't speak for DD.
1) My SAC is .5 on a bad day in So Cal, .4 on a good day
2) The SS is optional, if you are using a 6CU bottle, you have a totally different mindset than a full sized pony
3) If you drill with your redundant air, their is no reason you should hoover your air. You have air, you know it, just ascend.

I do have a 6, a 13 and a 30 cu ft pony. IMO, the 13 is the best balance between size and capacity. The 6 is crippled, you have to accept a direct ascent to the surface and assume everything else is OK and Mr. Murphy is not around to complicate matters. For that reason its not my first choice either, but in fact I have drilled many times from 75' and use ~3cu ft every single time. So it is enough to make the ascent, just not enough to give the extra margin of safety you many want.