Largest gas capacity aluminium cylinders?

[sea_ledford]

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!

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

We aren't moving much on the bottom either, we need to dpv to get to the bottom. We've had surface currents strong enough that even at full speed we can't make it to the down line from 50 or so feet downstream. Obviously we try to not get downstream in the first place, but it is challenging when the wind and current aren't going in the same direction. All it takes is a bad gear handoff from the boat, or a diver fiddling with something at the surface before getting on the trigger and we are stuck scootering back upstream.

All our deco is drifting. We contemplated doing a trapeze, but after dealing with the currents, abandoned that idea.

 

[grantctobin]

A pair of manifolded 7L cylinders is more than sufficient for a dive even 50% deeper. Having to make your own protocol to switch gasses in the event of bailout (or even making your own rig protocol) is batshit. Compare what you’re doing to something like the Mars project or even the survey being done in some of the deeper caves in Florida and you’ll find that…it’s really really tame.

Get a pair of AL40s or 7L manifolded and a slung AL72/AL80 of 50% or even 50/20 to make it lighter on a leash as @elmo suggested and be done with it. Could even anchor an Ali80 to the ground and rotate it every few days, and then switch your leashed 80 to a 40 or similar.

To add more noise: a 300b 12L of 18/45 at 300b (if you can get it boosted to there) isn’t even 3,600 Litres! Gas isn’t linearly compressible esp at such high pressures. You’ll get ~3033L with such a fill. A 12L at 232b of 18/45 is ~2450L.

 

[RedSeaDiver2]

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

Thankfully yes.

 

[RedSeaDiver2]

We aren't moving much on the bottom either, we need to dpv to get to the bottom. We've had surface currents strong enough that even at full speed we can't make it to the down line from 50 or so feet downstream. Obviously we try to not get downstream in the first place, but it is challenging when the wind and current aren't going in the same direction. All it takes is a bad gear handoff from the boat, or a diver fiddling with something at the surface before getting on the trigger and we are stuck scootering back upstream.

All our deco is drifting. We contemplated doing a trapeze, but after dealing with the currents, abandoned that idea.

Those are very real possibilities - we might have to have scooters available - just one more thing to consider.

 

[RedSeaDiver2]

A pair of manifolded 7L cylinders is more than sufficient for a dive even 50% deeper. Having to make your own protocol to switch gasses in the event of bailout (or even making your own rig protocol) is batshit. Compare what you’re doing to something like the Mars project or even the survey being done in some of the deeper caves in Florida and you’ll find that…it’s really really tame.

Get a pair of AL40s or 7L manifolded and a slung AL72/AL80 of 50% or even 50/20 to make it lighter on a leash as @elmo suggested and be done with it. Could even anchor an Ali80 to the ground and rotate it every few days, and then switch your leashed 80 to a 40 or similar.

To add more noise: a 300b 12L of 18/45 at 300b (if you can get it boosted to there) isn’t even 3,600 Litres! Gas isn’t linearly compressible esp at such high pressures. You’ll get ~3033L with such a fill. A 12L at 232b of 18/45 is ~2450L.

When you say a pair of manifolded 7L cylinders is more than sufficient bailout for a dive even 50% deeper - after how much bottom time are you calculating that to be sufficient bailout?

 

[grantctobin]

When you say a pair of manifolded 7L cylinders is more than sufficient bailout for a dive even 50% deeper - after how much bottom time are you calculating that to be sufficient bailout?

Part of me says “I’m not here to do the math for you dude” and the other half says “well someone might learn something in reading this train wreck.”

The thread has flipped from metric to imperial and back enough times, here’s an example:

Sheer **** hits the fan math at 300’ let’s say 2cf/min equivalent for 5min before you begin your ascent. 10ATM * 2cf/min = 20cf/min * 5 = 100cf used before ascent. Pair of American LP50 are closer to 8L but we’ll stick w them bc they’re the GUE normal. 3600psi/2640psi*50cf/1.15 compressibility factor*2bottles = ~118cf.

Toss this 300’ 30min in the ocean plan in (which is a shitload of dive in the open ocean) and a quick ascent to your 21/35 or whatever intermediate deco and you get the attached profile of 50/70.

Let’s bring this back to your 200’ profile and get something like the second attached image (and then add another 70cf of bottom gas used for the 5min CO2 brain dead idk what to do, can’t ascend, blagh blagh panic).

You do you, but I’d guess most of the people in this forum w extensive experience w profiles yours and longer or yours and deeper would add a scooter, backmount a pair of LP50s of 18/45 (or even maybe add a few more bips of helium), sling an 80 of 50% and (for the v conservative) a lightly filled 40 or 80 of oxygen and call it a day.

Sources and assumptions: math is above, have had a CO2 hit deeper than 60m, my sac rate in this dive planner is accurate and low, and really don’t want people pretending bottles on their back that they can’t see are remotely safe. Other than my Neanderthal 5min panic assumption, your limiting gasses in open water deep dive will be deco gas volumes, not backmount gas volumes, esp in this range.

 

[RedSeaDiver2]

Part of me says “I’m not here to do the math for you dude” and the other half says “well someone might learn something in reading this train wreck.”

We certainly don't have a need for you to do the math for us - we have already done it.

The thread has flipped from metric to imperial and back enough times, here’s an example:

Well there is only one country that is to blame for the imperial bits - and that's your country not mine...

Sheer **** hits the fan math at 300’ let’s say 2cf/min equivalent for 5min before you begin your ascent. 10ATM * 2cf/min = 20cf/min * 5 = 100cf used before ascent. Pair of American LP50 are closer to 8L but we’ll stick w them bc they’re the GUE normal. 3600psi/2640psi*50cf/1.15 compressibility factor*2bottles = ~118cf.

Toss this 300’ 30min in the ocean plan in (which is a shitload of dive in the open ocean) and a quick ascent to your 21/35 or whatever intermediate deco and you get the attached profile of 50/70.

I've got no idea why you are evening talking about a 300 foot dive when I'm not and haven't... it seems like you are trying to start a pissing competition...

Let’s bring this back to your 200’ profile and get something like the second attached image (and then add another 70cf of bottom gas used for the 5min CO2 brain dead idk what to do, can’t ascend, blagh blagh panic).

You do you, but I’d guess most of the people in this forum w extensive experience w profiles yours and longer or yours and deeper would add a scooter, backmount a pair of LP50s of 18/45 (or even maybe add a few more bips of helium), sling an 80 of 50% and (for the v conservative) a lightly filled 40 or 80 of oxygen and call it a day.

Sources and assumptions: math is above, have had a CO2 hit deeper than 60m, my sac rate in this dive planner is accurate and low, and really don’t want people pretending bottles on their back that they can’t see are remotely safe. Other than my Neanderthal 5min panic assumption, your limiting gasses in open water deep dive will be deco gas volumes, not backmount gas volumes, esp in this range.

But you said "A pair of manifolded 7L cylinders is more than sufficient for a dive even 50% deeper." but now you are talking a pair of 18/45's and a slung 80 of 50%. What happened to the pair of manifolded 7L cylinders being sufficient bailout for a dive even 50% deeper? Given that a manifolded pair of 7L will be one gas - exactly what gas are you bailing out on from 300 feet?

 

[grantctobin]

We certainly don't have a need for you to do the math for us - we have already done it.

Well there is only one country that is to blame for the imperial bits - and that's your country not mine...

I've got no idea why you are evening talking about a 300 foot dive when I'm not and haven't... it seems like you are trying to start a pissing competition...

But you said "A pair of manifolded 7L cylinders is more than sufficient for a dive even 50% deeper." but now you are talking a pair of 18/45's and a slung 80 of 50%. What happened to the pair of manifolded 7L cylinders being sufficient bailout for a dive even 50% deeper? Given that a manifolded pair of 7L will be one gas - exactly what gas are you bailing out on from 300 feet?

The math is the evidence of a pair of 50s + slung bottles being sufficient for significantly deeper dives as deep bailout.

I’ll rephrase my above post:

Putting two different mixes on your back that you cannot identify is farm animal stupid. Don’t reinvent the wheel: don’t rely on a single first stage to guarantee both diluent and bailout, be able to visually see and identify the BOTTLE of whatever you’re gas switching to, and don’t die. Your above plan is silly and I hope you read into some of the buoyancy characteristics of various carbon cylinders before paying for them and realizing how buoyant some of them are.

 

[inquis]

I've got no idea why you are evening talking about a 300 foot dive when I'm not and haven't...

Unless I'm mistaken, that was simply illustrating the validity of the "50% deeper" statement. Your BO scenario is less demanding, wouldn't you agree?

 

[RedSeaDiver2]

Putting two different mixes on your back that you cannot identify is farm animal stupid. Don’t reinvent the wheel: don’t rely on a single first stage to guarantee both diluent and bailout, be able to visually see and identify the BOTTLE of whatever you’re gas switching to, and don’t die. Your above plan is silly and I hope you read into some of the buoyancy characteristics of various carbon cylinders before paying for them and realizing how buoyant some of them are.

Everyone is entitled to their own opinions of course.

We are satisfied that our method of having an information tag on the second stage of each bailout that shows the gas and MOD of the gas feeding the second stage, and having a cover pouch over the second stage of the 50% overcomes not being able to see the same information on the cylinder itself.

The first stage that is supplying the descent/bottom dil only provides gas to the CCR - it is not part of the bailout plan, and if a diver were to somehow lose both their deep ascent and shallow ascent bailouts (which are also their planned ascent dil) they can still ascend on the CCR using the bottom dil.

Using CCR for entire dive
- (as planned) bottom dil then switching to deep ascent dil before leaving bottom then switch to shallow ascent dil - runtime is 140 minutes
- (loss of deep ascent dil) bottom dil used for ascent until switch to shallow ascent dil - runtime is 147 minutes
- (loss of shallow ascent dil) bottom dil then switching to deep ascent dil before leaving bottom - runtime is 147 minutes
- (loss of both deep and ascent dil) ascend on bottom dil only - runtime is 167 minutes

Bailing out to OC at end of bottom time -
- bail to deep bailout (also serves as deep ascent dil) gas then shallow bailout (also serves as shallow ascent dil) - runtime is 185 minutes

I have emailed CarbonDive asking for information about the buoyancy characteristics of their cylinders, I'm not planning on using full composite cylinders as they would be too buoyant (I've used similar cylinders on SCBA cylinders while firefighting and know how light they are).