Big Heavy tanks!

[berndo]

its a guesstimate with the hopes that no OOG emergencies exist.

That's nonsense you heard and are repeating. Can you give an actually realistic scenario where is doesn't work? Min gas makes sense for deco dive where the can't ascent directly, it's silly for run of the mill ndl dives.
I've actually HAD OOG situations/free flows in real life back when we still dove only one first stage in cold water.

Given that we have no idea who you are

I don't know who you are. You're some random dude posting on the internet.

 

[scubadada]

Hi @jordaof

There is a long discussion and poll discussing average gas consumption on SB

Average Gas Consumption

There has been extensive discussion lately regarding average gas consumption. A poll may help give us a better idea of what the normal distribution of RMVs is. 1 cu ft = 28.32 liters 1 liter = 0.035 cu ft 28.3 l/min

scubaboard.com

It turns out there are no universally accepted definitions of SAC and RMV. However, to be useful in the estimation of gas needs, the calculation needs to be in volume of gas/time/atm. I define SAC as pressure/time/atm and RMV as volume/time/atm

Question - Definitions for SAC and RMV?

This topic comes up over and over. Let's see what you think. Please vote once for SAC and once for RMV or vote for #5 and elaborate in your post or #6 if you don't know what this is all about.

scubaboard.com

I run MultiDeco on my computer. The configuration uses only the term RMV and not SAC. It asks for volume units in imperial or metric.

The Shearwater Cloud only calculates SAC and not RMV. SAC is in pressure/time/atm

My very old version of Pelagic Pressure Systems Oceanlog reports SAC in pressure/time/atm and RMV in volume/time/atm. As you see there is a default cylinder in the calculation or you can change to another one.

 

[_sgm_]

Whoever slapped your hands was mistaken they're just different terms for the same thing.

Screenshot from multi deco shows them being used interchangeably
View attachment 808437

Story time to set the [frame]
------------------------
Reality and History
------------------------
Case in Point [the computer Industry 1978~idocracy1998 and beyond ] when we called ram out by the specific (design specs) 1x8 / 1x9 Dram, simm, sipp, dimm all was good you knew what you were getting would work... then the [masses] came into the industry and called them "sticks" because they could not comprehend the proper terminology for the item nor knew the difference for the terms in the industry... then the [masses started writing books and online (posts) documents for other {people} defining terms they made up... thus it devolved to the (Least Common Denominator) ...
1993~present with the internet any [entity] with a pc can write lunacy and it will become reality {I am partly to blame for giving that level of power to the savages over the past 38 years}.
I now understand why the proverbial greek gods punished prometheus.... ( humanity was not ready )
------------------------
SAC v RMV
------------------------
well the (rate) you have listed in multi-deco is at what atmosphere? surface....? because you would not use your (RMV) rate from 4 Atmospheres in your (SAC) calculation .... for your next dive plan... unless you wanted a really short dive and to come back to the surface with more air than intended
------------------------
LOGIC v CULT
------------------------
if there is a middle ground this article covers it best
WHY?
[1.] it can be tied to a veteran diver
[2.] not written by a no name clown who regurgitates web articles written by non divers
[3.] course material written by non divers in a marketing division
eg.( deco proc vs Nitrox / Advanced Nitrox) not naming any organization )

RMV vs. SAC: What’s the Difference? - Cave Diver Harry

Few topics generate more confusion than Respiratory Minute Volume (RMV)and Surface Air Consumption (SAC). Here is what you need to know.

cavediverharry.com

rewinding the clock (when we needed to buy and read books when I was doing Iantd we used SAC rate.... fast forward some years later many continents later.( RMV and SAC were being used interchangeably ) i thought OK same meaning different term.... ok.... no so much
------------------------
CLOSING
------------------------
Do I want to play one up tag with you for days? NO!
I really do not have the time as I need to prepare for my 2 months in Asia Pacific scuba diving... flight leaves in a couple days from Orlando.
I will leave you with that video which many certifying training authorities knitting circles agree with....

Before it even comes up.... I started diving in 1984 got certified in 1987 I forgot how many dives i have done because i never log them this is my hobby not my life i do this to be happy ( I am not here to collect trophies and get badges ) I am here to relax from the idiots I deal with everyday in the Informaiton Technology clown world... up until this year this month I never dove with a computer only tables, two stopwatches plus a depth gauge ( oil filled cressi 1986 ) ...[plan your dive; dive your plan]

getting old sucks, now I need readers for gauges which mean prescription lenses which meant begrudgingly I had to get a dive computer as a backup...
Times change and the computer is required for the diving today it used to be a luxury item...
there is my .02 cents take it for what it is worth.
Best regards,
SGM

 

[wetb4igetinthewater]

That's nonsense you heard and are repeating. Can you give an actually realistic scenario where is doesn't work? Min gas makes sense for deco dive where the can't ascent directly, it's silly for run of the mill ndl dives.
I've actually HAD OOG situations/free flows in real life back when we still dove only one first stage in cold water.

So, you said:

Have you never guided people? Depending on the dive site and max depth of 30m you turn at either 100 or 120 bar and swim back in shallower water. It's pretty much the standard and works, at least it worked for me with several thousand divers.

I'll assume that you start with 200ish bar. Approximate half of the gas. So, you have your customers drain their cylinders to 120 bar. Then one has an issue where they are losing gas quickly, an OOG emergency. What do you do? By sharing gas, how far will you get? Do you go to the surface? That's what I was asking here which you failed to answer:

If you have an OOG emergency at the turning point, do you have enough gas to get back? Or do you go straight to the surface? What is the boat traffic like there (if any)? How about current?

While it is nice that you had an OOG situation, did you ever have it at the turning point?

I don't know who you are. You're some random dude posting on the internet.

Yes, I hide behind my username. No wait, what are all these links in my signature? Oh there are documents there with my name and even my email address.

Yes, that's what randos do. Post identifying information. You got me!

 

[scubadada]

Hi @jordaof

Please help me understand your gas consumption and cylinder choice decision.

Is your 12 liter cylinder aluminum or steel? What is its working pressure? You stated that you start at 200 bar/2900 psi. An AL80 cylinder has a working pressure of 207 bar/3000 psi.

Is the 15 liter cylinder you will be trying aluminum or steel. What is the working pressure? An AL100 has a working pressure of 227 bar/3300 psi. I suppose a steel cylinder could have a variety of working pressures and gas content.

I would have the same questions for the 18 liter cylinder.

Knowing your current average gas consumption could be very useful for your choice of cylinders. From your initial post it appears you are doing about 45 min at 11-12 meters before you start your ascent. It you want to get an hour out of the dive, it would be easy to calculate the gas requirement. It looks like you need about one third more available gas.

Best of luck in you future diving.

 

[rx7diver]

All these terms and confusion! OMG! This stuff is really not that complicated. My open water course was in 1986, a university NAUI/YMCA semester-long course that had been taught "forever" by the same instructor--you know, starting back when people dove without an SPG or without a reliable SPG.

We were taught that it is important to calculate our "air consumption rate at depth" (ACRD) simply because a well-planned dive requires that you do this. And if, after a certain elapsed time at a given depth, your SPG is not reflecting what your prior calculations tell you to expect, then you "know" that your SPG has malfunctioned. Simple. We used the "The New Science of Skin and Scuba Diving, 6th Ed." (1985, Council for National Cooperation in Aquatics) as one of our textbooks.

I am not sure why some people debate the usefulness of this, whatever you or your particular training agency calls it currently.

rx7diver

 

[berndo]

I'll assume that you start with 200ish bar. Approximate half of the gas. So, you have your customers drain their cylinders to 120 bar. Then one has an issue where they are losing gas quickly, an OOG emergency. What do you do? By sharing gas, how far will you get? Do you go to the surface? That's what I was asking here which you failed to answer:

Do you understand that rec diving is when you can ascent without deco stops or swimming back to the boat underwater? 120 bar is PLENTY to deal with any situation within rec and ndl range.
Your whole argument is silly. Min gas doesn't even give you turn pressure, it give ascent pressure, which is kinda pointless is rec diving to begin with.

Yes, I hide behind my username. No wait, what are all these links in my signature? Oh there are documents there with my name and even my email address.

Nobody cares about what your real name or email address is. So your name is kosta... so what?

Is your 12 liter cylinder aluminum or steel? What is its working pressure? You stated that you start at 200 bar/2900 psi. An AL80 cylinder has a working pressure of 207 bar/3000 psi.

Is the 15 liter cylinder you will be trying aluminum or steel. What is the working pressure? An AL100 has a working pressure of 227 bar/3300 psi. I suppose a steel cylinder could have a variety of working pressures and gas content.

I would have the same questions for the 18 liter cylinder.

All standard euro tanks are steel and between 200 and 232 bar. (200 tend to be older, most newer tanks are 232). There are 300 bar tanks but they're not very common and most places don't fill more than 200-230. So every time you hear a European diver say x liter tank they mean steel and 200-232 bar. There are AL80 here but really only used as either sidemount tanks or stages. I have never even seen a AL100. AL tanks aren't really a thing in Europe. He will be trying steel. There aren't any 15 or 18 liter AL tanks. They would be a nightmare to dive with.

 

[scubadada]

...All standard euro tanks are steel and between 200 and 232 bar. (200 tend to be older, most newer tanks are 232). There are 300 bar tanks but they're not very common and most places don't fill more than 200-230. So every time you hear a European diver say x liter tank they mean steel and 200-232 bar. There are AL80 here but really only used as either sidemount tanks or stages. I have never even seen a AL100. AL tanks aren't really a thing in Europe. He will be trying steel. There aren't any 15 or 18 liter AL tanks. They would be a nightmare to dive with.

...Who cares?

I guess Scubadaba does, since he asked about it...

Yes, I was interested in hearing about cylinders used in Europe and appreciate the response. I have never dived in Europe. The liveaboards I've done in the Red Sea, Eastern Pacific, and the Caribbean have all offered AL80s and AL100s. All the operators I use in SE Florida offer AL80s, and HP steel 100s, often also 120s. So, now I have a better understanding of the posts from divers from Europe.

@jordaof started this thread asking for some reasonably simple assistance. This thread veered off into the increasingly common bickering among responders. It would be great if we could keep the arguing down.

 

[_sgm_]

.

 

[formernuke]

Turn pressure and ascent pressure should be determined based on site, depth etc even for recreational dives.

Knowing your sac can help determine this. Is it essential for recreational diving, no but it adds and extra margin of safety which is always a good thing.