redundant gas supply for rec diving

[mjhlaw]

A growing number of dive charters in the Great Lakes are requiring some form of standalone redundant air system for dives over about 60 feet. Part of the reason is the extreme cold, especially in the northern Lakes, can cause regulator freeze up, even in summer months.

I have been discussing the merits of different setups with local divers and solicit responses from a broader audience. Most of the tech divers suggest a sling mounted setup in 30 cf minimum size. Others say this is big overkill for no decompression dives in 110 ft. or less. Many wear a pony-type setup mounted to the main tank(s) because, although more drag, it is out of the way.

I have never carried a redundant air system but am shopping for one now. I am leanign toward a 30 cf aluminum with a quality reg and pressure guage on a 6" hose mounted to the main tank(s) on the left side (valve up) with a standard size reg hose clipped to the left side under the octopus. I understand that this rig will be heavy and will tip my balance a bit, but I want to have a substantial enough tank to give me enough air to safely ascend and safety stop. My thinking is that if bugs me enough, I will simply wear it slung tech style on my left. Becuase I dive steel 95's and 100s exclusively, and because I am fairly good on air, and because I do not plan to push the rule of 3rds or deco, I am not looking at this rig as anything other than a really good emergency backup.

What are your thoughts?

 

[Big-t-2538]

To be honest, the pony debate has been around for some time...and it's readily evident on this board.

MY personal feeling are that pony's are useless. I just don't see the benefits of a pony outweighing their cost. First, you need a tank & valve. Second, you need another reg. Third, you need an SPG you can trust and read while u/w. Fourth, you need to maintain the bottle and reg just like you do the rest of your gear. Now...once you have all that, you have to adjust to diving with a slung pony and using it. Mind you this will also make your profile in the water bigger, thus your drag will increase, and you'llbe working harder u/w...all to carry gas that you can't use inless it's an emergency.

After all that, then people generally say a 19 cu ft. tank is plenty. What??? all that $$$ & work for only 19 cu ft. of gas...that I might use 1 time? How much would it cost to get a second tank and double up your current setup with an isolator manifold and essentially double the amount of gas you carry? Which IMO is a more reliable redundant system. Why? B/c the extra gas that you get, you can use. Yes, you will probably work harder with doubles, but there will be a benefit....Increased Bottom time b/c your gas supply is larger.

If you decide to get a pony, please make sure it's well maintained, practiced with so you're proficent with it in an emergency, and big enough to get your butt back to the surface. Think about how much gas you would need to reserve for a 100' dive making the proper safety stops and ascent rates when your panicked.

-T

 

[DA Aquamaster]

I went with a pony for the same reasons here as water temps tend to run in the low to mid 40's at depth even in the summer. I found however that once I started doing some intentional deco dives below 100 ft that a 15-19 cu ft pony was not really adequate and switched to a 30. You need to follow rule of thirds planning and then carry at least the same amount of air as that 1/3 in the pony to fully meet any ascent/deco obligations in the case of a failure of the primary system. A 30 cu ft pony will at least have some ability to function as a deco tank if you go deeper/longer later and a 40 would be even better. If moving to a 30 or a 40, from a 19 the weight increase is relatively small.

When I dove with a 30 cu ft pony, I used a standard SPG and routed it around the right side along with the second stage mounted like a conventional octopus. But in practice, the SPG is not needed as long as you check the pony pressure prior to the dive as, if you are using the pony at all, you are (or should be) on your way to the surface and you either have the gas required or you don't. All the SPG adds to the system is the piece of mind during deco that you have enough gas left.

Using an SPG on a 6" hose only makes sense if you plan to rig it as a stage bottle. Otherwise the SPG/6" hose is just another entanglement hazard as you won't be able to see it underwater anyway. A button gauge on the first stage would be less accurate but more appropriate for back mounting purposes as would an SPG on a conventional lenght hose if you want to see what you have left at any point in time.

Back mounting an AL 30 as a pony does not create much of an issue with trim and what little trim issue exists is easily offset with moving a couple of pounds to a pocket on the opposite side.

That said, my 30 cu ft pony use was a very transitory thing as I quickly discovered that a set of independent doubles made a lot more sense for the variety of diving I do and offerred a lot more flexibility for for not much more weight (twin steel 72's).

The 30 cu ft pony is now a stage mounted deco bottle allowing accellerated deco on Nitrox 50 and is worth considering as the accellerated deco allows more bottom time for the same basic run time which is always nice in cold water.

 

[cornfed]

MY personal feeling are that pony's are useless.

Useless!? Everything has it's place. For example, ponies are quite nice at the county fair where they provide a way to amuse your kid while you enjoy your beer.

 

[tedwhiteva]

Whatever you do, don't get a SPAREAIR if you are diving below 33 feet

 

[mjhlaw]

Thanks for the great feedback. I understand that this debate has been around for a while, including on this site. Still, your comment about the 6" hose being useless underwater mounted to a tank makes perfect sense, but with all the different suggestions I have been getting locally, I think I improperly combined different ideas. A full length hose would obviously be the only way to go with a tank mount.

I do understand that dual tanks with isolation and seperate regs would be better for deep and tech dives, but I am trying to accomplish a realistic backup without the weight and investement of such a rig right now. Duals add the of a new bc, backpack, valves, rings etc. and I really don't need all of that weight, aggravation, or expense at this point. I have to believe there are plenty of others out there that are in a similar situation.

I went with a pony for the same reasons here as water temps tend to run in the low to mid 40's at depth even in the summer. I found however that once I started doing some intentional deco dives below 100 ft that a 15-19 cu ft pony was not really adequate and switched to a 30. You need to follow rule of thirds planning and then carry at least the same amount of air as that 1/3 in the pony to fully meet any ascent/deco obligations in the case of a failure of the primary system. A 30 cu ft pony will at least have some ability to function as a deco tank if you go deeper/longer later and a 40 would be even better. If moving to a 30 or a 40, from a 19 the weight increase is relatively small.

When I dove with a 30 cu ft pony, I used a standard SPG and routed it around the right side along with the second stage mounted like a conventional octopus. But in practice, the SPG is not needed as long as you check the pony pressure prior to the dive as, if you are using the pony at all, you are (or should be) on your way to the surface and you either have the gas required or you don't. All the SPG adds to the system is the piece of mind during deco that you have enough gas left.

Using an SPG on a 6" hose only makes sense if you plan to rig it as a stage bottle. Otherwise the SPG/6" hose is just another entanglement hazard as you won't be able to see it underwater anyway. A button gauge on the first stage would be less accurate but more appropriate for back mounting purposes as would an SPG on a conventional lenght hose if you want to see what you have left at any point in time.

Back mounting an AL 30 as a pony does not create much of an issue with trim and what little trim issue exists is easily offset with moving a couple of pounds to a pocket on the opposite side.

That said, my 30 cu ft pony use was a very transitory thing as I quickly discovered that a set of independent doubles made a lot more sense for the variety of diving I do and offerred a lot more flexibility for for not much more weight (twin steel 72's).

The 30 cu ft pony is now a stage mounted deco bottle allowing accellerated deco on Nitrox 50 and is worth considering as the accellerated deco allows more bottom time for the same basic run time which is always nice in cold water.

 

[Big-t-2538]

I do understand that dual tanks with isolation and seperate regs would be better for deep and tech dives, but I am trying to accomplish a realistic backup without the weight and investement of such a rig right now. Duals add the of a new bc, backpack, valves, rings etc. and I really don't need all of that weight, aggravation, or expense at this point. I have to believe there are plenty of others out there that are in a similar situation.

Agreed, if you're diving a BC, you'll probably need a new one. However, if you're just buying something to pacify a charter boat, my personal opinion is that shelling out exrta $$$ for cumbersome gear is a waste. If you dive with good buddy principles, and an adequate gas reserve, that should suffice.

Frankly, I think the cheapest redundant gas supply for a charter boat would be an H or Y valve for your single tank set-up. It provides complete regulator redundancy with the exception of having a seperate gas reserve. IT will not prevent against a tank neck o-ring blowing. You have redundant regs, so if one freeflows, you can thumb the dive, shut it down and surface with the remaining gas on the functioning reg....with your buddy.

 

[chrisch]

You might want to think about an H valve (or Y valve although I think these are no longer available) They are not popular in the US or my home the UK, but here in Europe they are very common.
This gives a shut down facility and two seperate regs, but on a single tank.
Downside is no spare gas, but since the main prob is likely to be a freeflow (esp in the cold water you mention) this shuts off the flowing reg. Just like a twinset but with less gas overall.
Like everything it aint perfect, but its a lot easier than a pony.
If you go deep enough then twins are really a prerequisite. When you get to that point you already have two regs and are used to valve shutdowns.

H Valve is around $80.

Chris.

 

[cool_hardware52]

Have you considered Twins? By twins I mean independent single cylinders. The second cylinder is kinda the ultimate pony. Our back plate will accomodate twins as will our 50 lb wing.

Regards,

ch

 

[hex92]

Thanks for the great feedback. I understand that this debate has been around for a while, including on this site. Still, your comment about the 6" hose being useless underwater mounted to a tank makes perfect sense, but with all the different suggestions I have been getting locally, I think I improperly combined different ideas. A full length hose would obviously be the only way to go with a tank mount.

You don't really need any kind of pressure gauge on your pony. I think someone else mentioned this too. If you are using your pony you are obviously calling the dive. So you either have enough air or you don't. Having a guage isn't going to change that.

I don't have a gauge on my pony at the moment, but I will probably put a button gauge on there at some point since my pony reg is yoke and my primary is DIN. Which means I have to borrow someone else regs to check my pressure.