Largest gas capacity aluminium cylinders?

[RedSeaDiver2]

FTFY…

I figured this too. Not archaeologists per se, but a person in a new environment thinking about their desires and inherent assumptions masked as needs, and assuming they have the best handle on the balance of factors of their ‘highly unique’ ‘requirements’ ‘necessary’ for success.

175-200’ dives are really not that uncommon. I did 4 of them in a single weekend less than a month ago, and I’m a baby in that area of diving.

You ignore or reject the lessons of those experienced divers at your peril. Deeply consider Chesterton’s Fence: the concept that you should not come up with changes until you know why things are done how they’re done.

It’s not that you don’t have different needs or that there isn’t a better ways, because you might. Rather, it’s the idea that until you know the why of the current process, you’re more likely to *degrade* rather than improve the process.

The fact that you don’t understand why steels are preferred to aluminum tanks (they are often no heavier due to their superior strength and when you factor in the extra lead to get the tanks to stay negative are much *lighter* overall) leads me to believe you don’t fully understand the problem space yet.



Also not unique to archaeologists: *very* common for people for whom scuba is merely a tool rather than a focus — or maybe more accurately an *obstacle* to be subjugated quickly and without regard to anything else. Their goal is often to translate their current intuition and experience as directly as possible to the new environment.

Usually to their own difficulty, if not outright harm. The environment doesn’t care about your intuition…

What we are doing is not all that different to how GUE set up their JJ rebreathers - 2 cylinders of bailout gas on the back with the back-mounted rebreather. The changes we are making are mostly changes that are necessary - e.g. our bailout needs to be two different mixes so we won't be manifolding the bailout cylinders together, and we need more bailout gas than their 7 litre bailout cylinders so we will use bigger cylinders. Kneeling on the sand is the usual way for this kind of thing as it works the best for what we are doing.

 

[elmo]

I'm not a tech diver, but this sounds extremely dangerous. How are you going to verify that first breath at 200' is off the 18/40 bottle? It seems unlikely that you'll be able to follow standard verification procedures with back mounted independent doubles.

For example: How to Switch your Diving Gas

This is a real concern and people have died because they didn’t take it seriously. Switching to deep bailout “blind” isn’t going to kill you. But backmounted 50% on a 60m/200’ dive is a whole other story.
@RedSeaDiver2 is there any reason not to keep the 50% deco gas in an AL80 behind you on a leash? Bring it forward when you need it, which won’t be when you’re on your hands and knees on the bottom.

 

[RedSeaDiver2]

I'm not a tech diver, but this sounds extremely dangerous. How are you going to verify that first breath at 200' is off the 18/40 bottle? It seems unlikely that you'll be able to follow standard verification procedures with back mounted independent doubles.

For example: How to Switch your Diving Gas

Not extremely dangerous if properly risk-assessed and proper controls put in place. In our case, we will label the cylinders, but we will also have tags on the second stages with the same information and then make sure that the second stages match the cylinders that they are connected to after assembling the gear. The deep bailout won't be hypoxic so it can be safely breathed at any depth, the 2nd stage of the shallow bailout will have a cover on the second stage to serve as an additional reminder that it isn't suitable for all depths.

 

[inquis]

If they are OK then 2x the Worthington Carbon Dive Cylinders will weigh about 11kg less than 2x the Fabers in the same size - which my back will thank me for.

I'd be surprised if the rig is substantially lighter overall than with steels. There is no free lunch -- carbon tanks will require you to use more lead to be neutral.

 

[RedSeaDiver2]

I'd be surprised if the rig is substantially lighter overall than with steels. There is no free lunch -- carbon tanks will require you to use more lead to be neutral.

Given the water temps we won't be wearing really thick exposure protection so these might put us pretty close to neutral.

 

[Ahereng]

A guy that dives a lot where I often dive use the Carbondive 12l tanks for bailout, and is happy with them. He has attached a 1kg weight on the bottom of the tanks to somewhat help with the boyancy.

 

[RedSeaDiver2]

A guy that dives a lot where I often dive use the Carbondive 12l tanks for bailout, and is happy with them. He has attached a 1kg weight on the bottom of the tanks to somewhat help with the boyancy.

Many thanks @Ahereng - that is some really helpful information.

 

[sea_ledford]

Have you done a mockup with two 80s/11L(or whatever is semi close to the correct size that you have available) strapped to the CCR? That seems like it would be unreasonably wide and you would lose arm range of motion because your elbows are hitting the tanks all the time. Can it even fit through a boat gate? Can the CCR support that much weight strapped to it? Planning on using bailout as dil as well or are you going to have another two 3L tanks for dil and O2?

I can see why you are looking at carbon tanks, that's going to be a 150lb+ rig.

It seems like standard sidemounted bailouts are an easier option, or even two on the left and one on a leash. What you are proposing sounds cleaner in theory, but will be a convoluted mess of hoses once you have it all rigged up.

You mentioned currents too. The deep water coral work I am doing in the Gulf of Mexico has variable currents. We thought we could get away with scooters being optional, but there is no way. It's required with CCRs, 2-4 bailouts and sampling gear. Just something else to throw into the mix incase you hadn't considered it yet.

Sounds like you are on an awesome project!

 

[RedSeaDiver2]

Have you done a mockup with two 80s/11L(or whatever is semi close to the correct size that you have available) strapped to the CCR? That seems like it would be unreasonably wide and you would lose arm range of motion because your elbows are hitting the tanks all the time. Can it even fit through a boat gate? Can the CCR support that much weight strapped to it? Planning on using bailout as dil as well or are you going to have another two 3L tanks for dil and O2?

Using the CarbonDive 12L tanks makes the entire rig only 80mm wider than the GUE JJ configuration, and I'm OK with that. I will probably get a couple of pieces of PVC pressure pipe that is about the same size as the CarbonDive cylinders to double check before I place an order for the CarbonDive cylinders. The boat for the project is going to have a diver lift and it will be plenty big enough for a rig this size. The Divesoft Liberty in its Heavy configuration can be set up in the GUE configuration like a JJ, and there is only a total of 4kg difference between 2x 7 litre steels like GUE use and 2x the CarbonDive cylinders - I think that it will handle it comfortably. Descent and bottom dil and O2 will come from 3 litre cylinders, then just before leaving the bottom will be a dil switch to gas from the deep bailout, then at 15 metres will switch dil to 50% from the shallow bailout.

I can see why you are looking at carbon tanks, that's going to be a 150lb+ rig.

It seems like standard sidemounted bailouts are an easier option, or even two on the left and one on a leash. What you are proposing sounds cleaner in theory, but will be a convoluted mess of hoses once you have it all rigged up.

Using the CarbonDive cylinders will reduce the weight by 11kg / 24lbs compared to using steels that hold the same amount of gas - this will hopefully put me about neutral. Hopefully I will be able to route and stow the hoses in a way that keeps things need - I've got a few ideas on this that I want to try.

You mentioned currents too. The deep water coral work I am doing in the Gulf of Mexico has variable currents. We thought we could get away with scooters being optional, but there is no way. It's required with CCRs, 2-4 bailouts and sampling gear. Just something else to throw into the mix incase you hadn't considered it yet.

We haven't really made a decision one way or the other on scooters - because the wreck site is reasonably small we won't be going horizontally very far during the work stage of the dive, so we are thinking that if divers can't get back to the trapeze etc then they will put up an SMB and drift deco with the boat following. Having said that there have been some sketches floating around of a wet submersible that takes advantages of the big leaps forward in battery and electric thruster designs - fit something like that with depth hold capability like ROV's have and life gets better!

Sounds like you are on an awesome project!

Totally awesome project - the dream is that we might find the oldest mariner's astrolabe that has ever been found - time will tell.

 

[Ahereng]

A little thing to consider regarding the Carbondive tanks, are you able to get 300bar fills at your destination?