DIR mental math for gas consumption

[Dan_P]

Why?

I suspect your SPG or computer is far more reliable than your brain during a dive.

The point is they’re NOT reliable.
They are accurate when working properly, but you cannot rely on them. Thus, their proper function must be confirmed.

How do you confirm that your SPG is accurate?


Standard training from OWD onwards over at UTD (no doubt GUE and ISE, too)

 

[BDSC]

The point is they’re NOT reliable.
They are accurate when working properly, but you cannot rely on them

Seriously? Not reliable? Can’t rely on them?

I now have well over 1000 dives and have never, ever, had a gauge or computer fail me. I have always relied on what they are telling me as far as how much air I have left and I have never run out of air.

Maybe my equipment isn’t the norm but mine has been very reliable.

 

[dave22387]

Seriously? Not reliable? Can’t rely on them?

I now have well over 1000 dives and have never, ever, had a gauge or computer fail me. I have always relied on what they are telling me as far as how much air I have left and I have never run out of air.

Maybe my equipment isn’t the norm but mine has been very reliable.

I literally just replaced a SPG for being innacurate. It didn't fail but was showing about 300psi high.

 

[rjack321]

Ive broken the glass in spgs
in the small plastic ones the face oring has failed and flooded it
they are often inaccurate by 200+psi

Saying SPGs are "forever" is a misnomer

 

[CptTightPants21]

The point is they’re NOT reliable.
They are accurate when working properly, but you cannot rely on them. Thus, their proper function must be confirmed.

How do you confirm that your SPG is accurate?


Standard training from OWD onwards over at UTD (no doubt GUE and ISE, too)

It's this kind of absolute statement that gives GUE and their ideas a bad name.

SPGs as a whole ARE reliable.

The correct answer is that a thinking and knowledgeable diver should be able to accurately estimate his gas consumption during a dive based on his dive profile and be able to estimate his future consumption based on the remaining dive plan.

Gas consumption charts are supplements to SPGs and another tool in becoming a total diver.

If your SPG hits your turn pressure, you are going to turn the dive. You are not going to say "Well, my SPG says I hit turn pressure, but my mental consumption math calculator tells me I still have 3.5 mins before I need to turn the dive so I will stay".

Do SPGs break, sure. So do computers, regulators, and every other piece of dive equipment. There are usually warning signs that a piece of equipment is on its way out and most failures should be caught on pre-dive checks before a diver goes in the water.

 

[PfcAJ]

It's this kind of absolute statement that gives GUE and their ideas a bad name.

SPGs as a whole ARE reliable.

The correct answer is that a thinking and knowledgeable diver should be able to accurately estimate his gas consumption during a dive based on his dive profile and be able to estimate his future consumption based on the remaining dive plan.

Gas consumption charts are supplements to SPGs and another tool in becoming a total diver.

If your SPG hits your turn pressure, you are going to turn the dive. You are not going to say "Well, my SPG says I hit turn pressure, but my mental consumption math calculator tells me I still have 3.5 mins before I need to turn the dive so I will stay".

Do SPGs break, sure. So do computers, regulators, and every other piece of dive equipment. There are usually warning signs that a piece of equipment is on its way out and most failures should be caught on pre-dive checks before a diver goes in the water.

^this

 

[Dan_P]

Seriously? Not reliable? Can’t rely on them?

I now have well over 1000 dives and have never, ever, had a gauge or computer fail me. I have always relied on what they are telling me as far as how much air I have left and I have never run out of air.

Maybe my equipment isn’t the norm but mine has been very reliable.

I‘d agree that 1000 dives in a row with no equipment failure is extremely lucky.
Choosing to depend on it to continue working, is the issue I’m addressing.

It's this kind of absolute statement that gives GUE and their ideas a bad name.

SPGs as a whole ARE reliable.

The correct answer is that a thinking and knowledgeable diver should be able to accurately estimate his gas consumption during a dive based on his dive profile and be able to estimate his future consumption based on the remaining dive plan.

Gas consumption charts are supplements to SPGs and another tool in becoming a total diver.

If your SPG hits your turn pressure, you are going to turn the dive. You are not going to say "Well, my SPG says I hit turn pressure, but my mental consumption math calculator tells me I still have 3.5 mins before I need to turn the dive so I will stay".

Do SPGs break, sure. So do computers, regulators, and every other piece of dive equipment. There are usually warning signs that a piece of equipment is on its way out and most failures should be caught on pre-dive checks before a diver goes in the water.

I feel we’re splitting hairs over addendums we’ll probably agree on in either case - I could further expand that developing awareness to facilitate mental calculation, benefits the diver well outside of the benefits strictly isolated to mental gas consumption on its own.

My point is overreliance is the problem.

 

[NAM001]

Quick question really aimed at you DIR guys... I really like the concept of your brain being your primary SPG. I already kind of do this, meaning when I look at my guage I expect to see around a certain number. This basically comes from experience.

My question is since it is specifically taught to GUE divers how do you guys do it? Is it just experience or is there math involved? The only way I can think of is multiplying sac/rmv by ATA. I really don't want to do that underwater if I don't have to. How is it taught to you guys? I consider myself pretty good at mental math considering I have to do it for work but I'd rather not underwater if there is some rule of thumb etc.

Someone school me please and thanks!

Here is a coupe of things that may help. If you know your sac or rmv what ever .consumption onthe surface. is say 1/2 cuft 1/2 cu ft is equal to some presure. So now yo have to know your tank al80 hp 100 etc. and find what 1/2 cuft is Ie on a hp100 then it is 1/2 of one percent of he contents. 3500 psi 1 percent is 35 psi and 1/2 would be 17.5 psi a minute. In 10 minutes you should use 175 psi on the surface. at 100 ft it is 4 times that much so in 10 minutes it is 700 psi. If you had a lp85 then the 1/2 cuft would be 1/170 of full tank 2640 psi

here are numbers for 1 cuft smv per minute it will be smv over tank capacity times full presure at 100 ft 4 ATA
tank % of full tank psi at full tank psi per minute depth in ata per minute
al50 1/50 2640 52 psi 208 psi
al 80 1/80 3000 37 psi 158 psi
lp100 1/100 2640 26 psi 104 psi
hp100 1/100 3500 35 150 psi

many people white the psi per cuft on the tank called a tank factor.....

some will argue that it is easier to work in metric.

 

[NAM001]

Seriously? Not reliable? Can’t rely on them?

I now have well over 1000 dives and have never, ever, had a gauge or computer fail me. I have always relied on what they are telling me as far as how much air I have left and I have never run out of air.

Maybe my equipment isn’t the norm but mine has been very reliable.

I have never had problems with spg's but the AI transmitters have all failed with a 300 psi error. they are all noticed with a full tank but the AI reads 300 lower ,,,,,,,,, whether or not the AI reading 500 is really 800 I dont know. I dont use transmitters any more.

 

[EireDiver606]

Beware, do not open a closed isolator underwater unless you analyzed both sides of your doubles.

In the first place never close the manifold when filling unless it’s on purpose.

I would not like that to happen..