Low on air done right?

[Gombessa]

Your rhetorical devices have been a combo of red herring & strawman, sort of like saying "the sun is not yellow it is yellow." Nice try, though.

Huh? That statement is indicative of neither a red herring nor a strawman argument.

 

[MXGratefulDiver]

NWGD, if you look in the student manual for OW1, you will indeed see what it says.

First off, there is no OW1 in NAUI. The class is called "Scuba Diver". And I'll be looking at the student manual this evening, in fact, while I'm teaching the class.

I'm not going to argue the point with you.

... Bob (Grateful Diver)

 

[nereas]

First off, there is no OW1 in NAUI. The class is called "Scuba Diver". And I'll be looking at the student manual this evening, in fact, while I'm teaching the class.

I'm not going to argue the point with you.

... Bob (Grateful Diver)

I know what it's called.

 

[IceBergSlim]

First you said this:

It is common for me to check my buddy's SPG, normally half way though the dive.

All the major training agencies teach that.

(which is wrong and wronger)

Then you said this:

Who knows? Maybe PADI does not require it????

I think the cyberdiver guru thing is not working out well for you.

 

[Ayisha]

...Consider that you'll generally consume about as much getting back as you used going out. Let's say that's 700 psi. Add your reserve (500 psi) and what you will need for a safety stop (let's say 200 psi for example) ... and your turn pressure is the sum of all of those (in this case, 1400 psi).

Bob, this sounds different than what I have learned. From your figures, if your reserve (including safety stop) is 700 psi, and you are starting with, for example, 3000 psi, your turn pressure would be 1600 psi, not 1400 psi. 3000 - 1400 = 1600 psi turn pressure. 1400 psi would be too low in this case, as it was in the OP's case.

However, the common way, I believe, to plan a dive on halves is to minus your reserve (rock bottom for a certain depth) from your starting tank pressure and divide by 2; Then minus that result from your starting pressure, which results in your turn pressure. For example, using your figures, 3000 - 700 = 2300. 2300 divided by 2 = 1200 (rounded up). 3000 - 1200 = 1800. Therefore, 1800 psi is your turn pressure, meaning that when any team member reaches 1800 psi remaining, it is time to head back.

The second method is a more common way of determining turn pressure, right?

 

[IceBergSlim]

Huh? That statement is indicative of neither a red herring nor a strawman argument.

This is even better: Editing an earlier post to try to hide ignorance.

Who knows? Maybe yours does not require it????

--------------------------------------------------------------------------------
Last edited by nereas; Today at 04:51 PM.

Needless to say the original un edited post was even more incorrect.

 

[MXGratefulDiver]

Bob, this sounds different than what I have learned. From your figures, if your reserve (including safety stop) is 700 psi, and you are starting with, for example, 3000 psi, your turn pressure would be 1600 psi, not 1400 psi. 3000 - 1400 = 1600 psi turn pressure. 1400 psi would be too low in this case, as it was in the OP's case.

However, the common way, I believe, to plan a dive on halves is to minus your reserve (rock bottom for a certain depth) from your starting tank pressure and divide by 2; Then minus that result from your starting pressure, which results in your turn pressure. For example, using your figures, 3000 - 700 = 2300. 2300 divided by 2 = 1200 (rounded up). 3000 - 1200 = 1800. Therefore, 1800 psi is your turn pressure, meaning that when any team member reaches 1800 psi remaining, it is time to head back.

The second method is a more common way of determining turn pressure, right?

Well, that works well for an out and back dive profile. What I was saying is that most people don't dive that way. For most dives ... people will swim to a destination, hang out there for a while, then either move on or begin their return ... again, dependent on the type of dive you're doing. My example was for that type of profile ... and in this case, assuming a shore dive where you'll be exiting at the same place you entered. And it was a simplified example.

If you simply divide your usable gas in half for a profile like that, you'll be cutting short the amount of time you potentially can remain at the destination and coming back in with more gas than you need. Now, there's nothing wrong with doing that ... on a lot of dives, there's plenty to see in the shallows if you get back to 20 feet or so with extra gas. And spending extra time in the shallows helps you offgas more efficiently, so I'm in favor of that approach if it's what you want to do.

But that wasn't what my example was intended to point out.

Basically, if you use a certain amount of gas going out, you'll need the same amount of gas coming back (assuming similar conditions and a reciprocal heading). Add that amount to your desired reserves and you have your turn pressure. In my example, desired reserves is 500 psi plus what you'll need for safety stop. In my example, that was 500 (reserves) plus 200 (safety stop) plus return (700) ... which is 1400 psi.

Again, this was meant to be a simplified example of a possible profile ... not a rule of thumb. I'm talking concepts. It also doesn't consider rock bottom, which may require you to leave the deepest part of your dive earlier.

Every dive profile is going to be different, and if you look at your dive plan as a series of "mini-dives", you can pretty effectively calculate how much gas you'll need and what an appropriate turn pressure should be. It's all explained in the article I referred to earlier ... which you can find on my web site. The key thing is getting people to think about it in the first place ...

... Bob (Grateful Diver)

PS - to nereas ... NAUI Scuba Diver manual ... page 72, upper left side of the page. The paragraph is highlighted. Before you tell anyone else what NAUI teaches, I suggest you read it.

 

[mania]

I believe the other half, on the experienced end, are usually extremely experienced, such as cave dives, shipwreck penetrations, and CCR dives. These are not "intermediate" divers. There are also a fair amount of old-age fatalities, such as heart attack victims on scuba, presumably due to overexertion. There are also a fair amount of fatalities that fall into the "left behind by the cattle boat" category, and also quite a few in the "dangerous beach entry" group.

Thallassamania has better access and experience to these statistics than I do.

Those statistic are published annually. You may find them interesting. Although they prove you are wrong. But all it takes is to read them.

 

[japan-diver]

I too get annoyed, particularly when I see novices making huge mistakes that endanger even newer novices.

The errors on this dive began during the planning stages, before going into the water.

Wearing different sized tanks was the first error.

Having a 3-man CF was the second.

Not paying close attention to the 3rd novice was the third.

Not proceeding to the safety stop immediately was the fourth.

Four failures. It's quite lucky that no one drowned on this dive.

Half of all scuba fatalities are by novices.

Nice try at a rhetorical reply, JHill. Not one that was very seasoned or logical however. I am sure you will get better at failure analysis with time, however. Everyone does, if they live long enough.

Now I have been away from the computer for awhile but had to answer this.

Different sized tanks not an error or did it in anyway contribute to the problem on the dive.

A three man team is not a problem and in many times is the prefered method- again in this case this did not lead to the problem on the dive.

Don't think there was that much inattentiveness on the dive - turned at planned pressure- noticed team member three was using air faster on the way in and used the agreed upon plan to deal with the situation (An example that would lead me to believe that the OP may have had at least adequate instruction)

Preceding to the safety stop immediately- not really a failure- team still had two ponies and more back up air available- no emergency happening here, exit as planned.

I will say it again poor planning on turn pressure but more good than bad on this dive. Nereas maybe you should look at your analysis better and in looking at some of your suggestions they are dangerous and could lead to those drownings you keep reffering to...

 

[ScubaAndDreams]

NWGD, if you look in the student manual for OW1, you will indeed see what it says. And that is what I have tried to encourage here.

Your rhetorical devices have been a combo of red herring & strawman, sort of like saying "the sun is not yellow it is yellow." Nice try, though.

I hope the O/P in his next dive will heed all the advice given.

All I have to say is that I am glad that Bob has the stamina and perseverence to lay out a logical argument against your utter BS. Again, the advise you render to new divers seeking information on scubaboard is bordering on the dangerous...

If you insist on giving new divers advise I would hope that you would take the time that Bob did and not only explain the "how" but also the "why"....

Then again, you can't even get the "how" right.