Big Heavy tanks!

[Angelo Farina]

Yes, I know, but people falsly claimed it's not explained in the class. I just corrected the fake news.

The concept of SAC was introduced and, if I remember correctly, a typical value of 20 l/min was suggested.
But in none of the check dives my sons were requested to plan the dive computing the amount of gas required, the rule was simply to signal the instructor when the SPG was at 100 bars.
And yes, that was the "turning point", not the "ascend immediately even if far from the boat". That was set at 50 bar. And it was expected a minimum pressure of 30 bar when back on the boat. The AOW course was on a LOB in Cairns, Australia (Great Barrier).
The boat was typically anchored on a shallow sand bank at 6-10 m depth, so the time for ascending was just for the safety stop.
Ok, also this is some sort of minimal gas planning, but it is entirely different from the real gas planning as enforced in a Cmas course.
As I and my wife were on the boat, and, being instructors, we were allowed to dive on our own, but staying around to the students, we have seen how the lessons were conducted. Nothing dangerous, but limited to the very minimal skills as defined in the syllabus.
Our sons were very young, the younger was just 12, so we were slightly concerned about these PADI courses. They did not learn a lot, but the procedures were reasonably safe.

 

[Wibble]

Yes, I know, but people falsly claimed it's not explained in the class. I just corrected the fake news.

In your class it may have been explained, but it sure wasn't in the OW and AOW classes I attended and neither was it from some other comments on here. SAC/RMV is a very important concept for dive safety and people should be very aware of the amount of gas required to ascend safely from the bottom with a safety stop AND have sufficient reserve in case of any 'incidents'. That 50 bar (33 bar in the USA) reserve isn't optional and should be firmly enforced by the dive leaders -- you could easily need that for a surface swim or helping others.

Again, your dogma is showing. It is definitely not fake news that many people come away from OW utterly reliant on DiveMASTERs to tell them their pressures and guide them around.

If remember correctly, the concept of SAC was introduced and a typical value of 20 l/min was suggested.
But in non of tge checkbdives my sons were requested to plan the dive computing the amount of gas required, the rule was simply to signal the instructor when the SPG was at 100 bars.
And yes, that was the "turning point", not the "ascend immediately even if far from the boat". That was set at 50 bar.
Ok, also this is some sort of minimal gas planning, but it is entirely different from the real gas planning as enforced in a Cmas course.

50 bar should be the point at which you climb aboard the boat, not the time to leave the bottom AND do a safety stop. That 50 bar (or 33 bar if in the USA) is your emergency and contingency gas. Use that at your peril, especially if you habitually use it.

 

[Angelo Farina]

In your class it may have been explained, but it sure wasn't in the OW and AOW classes I attended.

Again, your dogma is showing. It is definitely not fake news that many people come away from OW utterly reliant on DiveMASTERs to tell them their pressures and guide them around.

Both my sons came out of their AOW without being prepared to autonomous diving on their own.
After the Cmas course, instead, they were fully autonomous.
It is not just matter of contents of the course, it is matter of approach to problem solving.
From what I have seen, in Padi a complete, fully autonomous diver is called a Master Scuba Diver, which requires a number of additional courses after AOW.
In Cmas (and Bsac) you reach full autonomous capabilities after just the first three-months-long course.
But, as said, the mentality is completely different. You are in a club environment, instructors are volunteers unpaid, and when a student needs additional lessons, you get them for free.

 

[formernuke]

Unless is was taken out recently, sac calculation is in the PADI and SSI OWD class and in the training material. What people have said here is not true.

Wasn't there when I did mine in 2008, not there when I did my IDC 2 years ago

 

[formernuke]

@berndo is saying some misleading and some false information.

I have personally witnessed dive ops in the US say if your back on the boat with less than 500 psi in your tank absent a emergency you will not be allowed back. Can't speak of other countries. OW class in PADI does not teach sac rate, the basic to do it is there as in the deeper you do the faster your tank goes. And be back with 500 psi.

A 1/2 tank + X is misleading.

So if you take your tank, let's say 3000 psi and subtract 500 you have 2500 to use on your dive. According to berndo you are turning around at 1750. This is flat wrong because you are starting your ascent now at 500, this means your using the 500 psi min for your ascent and safety stop. Congrats your now kicked off that dive boat.

The right way to do it, not taught is to say ok I need this much for my ascent, including a minute or two once I reach the line to start it, come up and do my safety stop. Knowing your sac is very useful here but most rec divers take a guess, it often works and with experience they kinda know how much gas they use to come up.

So let's say your shallow. You need 100 psi to ascend and do stop. You therefore need to start ascent with 500 plus 100 so 600 psi. That gives you 2400 for the descent and rest of dive including that one or two minute to sort yourself once you reach the ascent line. So 2400/2 is 1200 or turn at 1850 (1800 plus 50 for that one or two minutes). So even shallow that 1750 above is off by 100 psi.

If your deep you need more than 100 to ascend and do safety stop and that 50 to sort your self will change. If your at the rec limit you very well could be turning at 2000 or 2200 ect.

 

[curtistopping]

I notice that might be a problem of anxiety, explaining, I run through the first 50 bars, from 200 to 150 very fast, then I start to breath more calmly and air tends to last a bit more.

Could be the water temp I dive cold water and when I get in my tank pressure drops pretty fast in the first 5-10 mins then slows way down

 

[grf88]

For many years I enjoyed using my PST HP 130's and found them to be ideal for wreck diving in the Great Lakes. Now at 76 I find them a little too heavy and have switched to HP 100's back mount or LP50's side mount with a little extra from my home compressor.

 

[MidOH]

I can fit 120's, but prefer 100's and a slung al40 for more air.

 

[Eastwest]

All of my tanks are steel and pretty big , four hp 120's , four hp 100 's which make good doubles and two huge faber low pressure 131's and when filled to 3500 PSI having whole hell of a lot 175 cubic feet of air . This is for my 80 foot deep , 80 minute , 40 % O2 dive . No regrets with my steel tanks and welcome new diver . Goodtimes Rumdumb

 

[jordaof]

Just to give an adds up, I invested on a 15 liter steel scuba tank, and did deep and nitrox certs last weekend, and my experience:
The first early dive in Saturday was the deepest one to 38 meters "124 feet", of course I'm always on NDL as my other partners and buddies, so the 15 liter tank was more than adequate for the 7 minutes, with air, at that depth
The second dive was with nitrox, also with the same 15 liter tank, at a depth of about 25 meters, 82 feet, to visit a wreck, and again, the 15 liter was adequate, so I guess the 15 liter is the sweet spot for me, not to heavy, and gave me the same dive time as other divers with standard stubby 12 liter tanks.

Impressions: I was amazed with the Nitrox Experience, I felt a lot less tired than with air in all other dives, how I was able to check that out? I'm an heavy/fat guy, and it is always a challenge, although i can manage alone without problems, to climb the RIB metal stairs, the sea was a bit rough, and I felt that had a lot more energy when climbing, maybe it was placebo, but i felt that.

As a noob diver, with now just 30 dives, on the first dive of 38 meters "124 feet", my very first deep dive, I felt that to reach the surface "ascending" was a bit more challenging than other past dives i did with just 17 meters max "55 feet"

curtistopping -> I think you might be right, on the dives I lost the most air from 200 to 150 bar were those that i didn't wear a wetsuit at a water temperature of 59 Fahrenheit or 15 celsius, so I only dive with a 3 mm wetsuit now, and the difference although not impressive, gives me a better SAC.

Deep Certification -> 2 dives, one of them 38 meters with air
Nitrox 32% -> 1 dive, 25 meters