New Divers -- I need your help...

[rawls]

Peter...are you talking about first time open water students?
If you are then I pretty much guarantee you that you are going to have problems with this handout....Remember...Assuming these are new open water students, you are going to have to keep things simple and help them learn by giving non-diving examples. For example...telling them it is like planning a trip to somewhere and wanting to determine how much gas would be required to get there...Ya gotta keep it simple...Remember, these are students who know nothing about diving and there are going to be people with different age groups, educational background, etc and you need to explain in a way that they can all understand.

I know some people will disagree with me but I do not go into that much detail with that aspect of Boyle.

This is the version of my basic lecture about gas consumption. I include it in the Boyle's Law lecture.

If I give each one of you an 80 ft3 cylinder and attach a reg to it and tell you to breathe on it until you cannot take another breath, no one will end up finishing at the same time. Each of us have diffent lung volumes, rates of breathing, depths of breathing, etc. Say Sally cannot take another breath at the one hour mark. This means her cylinder will last her 30 minutes at 33 ft because you have twice the pressure pushing against you...so it is like taking 2 breaths at the surface. At 66 feet your tank will last how long?...the class answers 20 minutes...very good class Why...Because you are at 3 atmospheres, so your tank will last 1/3rd as long...EXCELLENT class!!! I am so proud of you So, lets say Sally does alot of dives at a confined shoreline where the bottom is at 33 feet and her 80 ft3 tank consistently lasts 30 minutes (low SAC I know, but this is to get across the point...and I tell them this). Then she goes out to the wreck offshore that is at 66 feet and her cylinder consistently lasts 20 minutes after several dives on the wreck. Say after awhile she has 20 or 30 dives and decides to take a deep diver class and she is going on a dive to 100 feet. Then I show them a table. This gives them their first brief look at tables. I say...when you get into the tables you will see the depths across the top...pointing it out...and the black numbers at the bottom show you the maximum times you can dive. So...For a 100 ft dive, you can stay down for a maximum of 20 minutes. How long will Sally's 80 ft3 tank last at 100 ft...About 15 minutes...She will be at 4 atmospheres so her tank will last 1/4 as long. She can do a dive for 20 minutes. Say the planned dive is for 15 minutes. At 15 minutes she will be out of air right...and she doesn't want to be out of air at 100 feet. So what this tells Sally is that she needs to have a larger cylinder to do that dive. Then I talk about how very important it is to look at your pressure gauge frequently. Then I go into the rule of thirds. A thousand pounds of pressure for the descent, a thousand for bottom time and a thousand for ascent...The point therefore that Boyle's law tells us is the deeper you go the less time your tank is going to last. And always remember to frequently look at your pressure gauge. And it is a good practice to use the rule of thirds when you are diving.

Again...Just remember, your class is going to consist of people who have different levels of learning and you need to make your lecture understandable for all of them. You want them to have a good experience in their learning. If you get some of the students confused then they will not have a good experience and will feel like learning to dive is too difficult to understand, when all that happened is that the instructor failed to teach in a way that everyone could understand.

Just some food for thought....

 

[dschonbrun]

Peter,

I get all the info, but the SAC rate of 1.0 is very conservative. The Tank factor seems un-necessary... to determine the PSI in a tank that equates to 25cf, you can use cross multiplication... for an AL 80, it works out to be... [25 / 80 ] x full tank PSI = PSI filling 25cf .

 

[Jim Lapenta]

I would also put in a simpler way of determining SAC. What I usually suggest is going to a familiar spot. Get nice and neutral at 30-35 ft, 33 would be ideal but 30-35 is close enough, and swim around maintaining that depth for 10 minutes. Keep track of the pressure used and then do the calculations for SAC. This is something that they can understand with a practical application thrown in that illustrates things clearly. Again keeping it simple.

Also you better check with the instructor before handing this thing out. You are probably finding out that the average ow class is missing alot of things you'd like to see. The instructor may resent you adding to his curriculum especially if it is a PADI class. They do not allow their DM's to do squat when it comes to adding to the materials taught. It's why I'm doing the crossover to YMCA and NAUI.

Right now under the supervision of an instructor we are preparing lectures, conducting confined water training and skills with the instructor overseeing and evaluating us and the students alike. Saturday I conducted my first academic class delivering a lecture on diving history, equipment, and diving physics. We had to prepare short presentations first, then do practice sessions with the instructor evaluating and critiquing us then actually deliver it to students. Finally since the instructor is an instructor trainer he has the option of having us give the complete lecture which he must first approve. It is a valuable experience putting a lecture together and presenting it while adhering to standards.

PADI wants you to spend a couple thousand dollars before you can tell a student anything. As long as we meet standards adding material that does not detract from the course and informs the student it is no different than an instructor who adds more to his courses. All of this must, of course, be approved first whereas a full instructor has alot of leeway and may add material as he/she sees fit.

I have no doubt that you only have the best interests of the students in mind. I also believe from your wife's posts you may in fact know more than a few instructors. The problem is in the PADI system you are not one and as a DM are severely limited as to what you can do while acting as one or while assisting in an official capacity. As one diver to another however that is a different story. But you must be very clear that that is all it is. If someone interprets your help as official instruction and somebody misuses it and gets hurt you could be opening yourself up for alot of bullcrap. IMO Better to follow the herd until you are in a position to change the direction of it with some recognized authority and the backing of professional liability insurance. My 2 cents.

 

[Kingpatzer]

Couple of thoughts.

First, cubic feet is abbreviated cu. ft., or ft³ (note that the 3 is a superscript and the f and t are lower case). FT3, Ft3, FT 3 and all the ohter variations you have are NOT abbreviations for cubic feet.

Pick a standard abbreviation and use it consistently.

The standard abbreviation for atmospheres as a unit of measure is atm not ATA.

You say that the range for female divers is typically less than the range for males. What is the range? Give it, or just give a general range and leave the gender out of it. By including a specific numerical range for males and an aside comment for females you suggest either that you're too lazy to look up the information or too sexist to care.

Leave out the "generally" when saying that the SAC rate goes up when a diver is stressed. There's no generally about it.

Set your math expressions in a distinct font that sets the math apart from the text and makes it easier to read. Center the expressions in the page on a line by themselves.

 

[spacemanspiff1974]

vplanner.

 

[Doc Intrepid]

Peter,

You're on the right track.

I'm aware that modern teaching methods are trying to cram 20 hours of material into 12 hours at best. Lots is going to fall through the cracks.

But half the issues on this board where noobs are discussing Spare Airs and Ponys are because they suddenly looked down one dive to discover they were nearly out of gas. Or their buddy ran out of gas. Or they had some sudden issue that resulted in some high excitement one afternoon.

If a diver doesn't know how to basically calculate how much gas they're going to use for a reasonably generic square profile, that diver has issues.

It is more complicated to do the math necessary to bake up a double batch of toll house cookies than it is to calculate how much gas you'll need for a dive involving given parameters of depth, time, and consumption rate.

Please.

Just because newly certified divers are ignorant of basic gas management does not mean that they need to remain ignorant. It simply isn't that tough, for anyone who cares to spend an evening figuring it out.

The hand-out is a step in the right direction. Some of these other guys have come up with some good ideas for tweaks.

Keep at it. I look forward to seeing what you come up with.

Being ignorant isn't shameful. None of us, especially new divers, truly know what we don't know.

Choosing to remain ignorant when there is a chance to become better educated on some important topic is where it turns into a shame.

Rock on, dude.

 

[Caleb Brown]

I've only been through about 12 dives so far, so I think I fit your intended demographic. I understood your Basic Gas Management Dive Planner OK and
I found it useful enough that I printed it to keep with my other Diving info.
Frankly, the Min Gas column is one that I haven't been thinking about on dives.
Me and my buddy both agree to signal "up" and "five" when either of us reaches
500psi (on AL80's). This included our deepest dive which went to a depth of 102ft.
(although we were only at that depth for about 5 minutes). We obeyed all safety
stop instructions from our dive computer on the way up. I surfaced with 300psi and
my buddy was down to 250. This is outside my personal safety margin and it could
have been a problem if for some reason we needed to share air from one tank (something that your chart factors in for us).
I need to go back and review my Dive training book to see which class I slept through
to miss this little detail. In the mean time, I'll use your chart.

Thanks

 

[TSandM]

Caleb, you didn't sleep through a class. This stuff isn't taught in OW, or anywhere else in the PADI curriculum.

 

[dumpsterDiver]

Too much information on one page.

No need to tabulate the actual volume of a tanks versus the stated size (the only one that diverges is the aluminum 80 and it is inconsequential particularly in relation to the SAC rate which is a gross approximation. It adds unneeded complexity to the table. The fact that an 80 has slightly less than 80 is a detail for scuba version of trivial pursuit.

The sentences at the bottom should have bullets.

I think lay people would rather read "cubic feet" rather than FT^3.

In the problem statement header, you state that the depth is 60 feet. You should also explicitly state in the header all the relevant "given" information which is essentially the assumed SAC and the prospective dive time.

I remember my first instructor teaching this to us and taught us that we also should assume a sac rate of 1.0.

There was no explicit reserve taught but he said to assume you use 1.0 cu-ft/min at the surface and 2 at 33 and 3 at 66 ft. etc. Divide the tank volume by the breathing rate at depth and see how long it will last on the bottom. Then knock a few minutes off. We didn't have pressure guages back then so, it was probably a suffciently detailed method back then.

This is essentially exactly what you are doing but adding the required reserve for each depth which you provide in a table.

 

[Peter Guy]

Keep those cards and letters comin' in kids!

OK -- some quick responses:

a. To those who have found it useful, Thank you.

b. Re the DM restriction -- Yup -- fully aware of the fact that I ain't an instructor (and have zero intention of becoming one) and that this can only be given out by an instructor (yes, I'm in the PADI system for this)

c. This is NOT intended for the OW student -- that student has too much thrown at them as it is. My intended audience is the AOW student -- especially one who is "planning" his "deep" dive for AOW (which I'll be monitoring this weekend for the first time as part of my DM "training")

d. I've decided to change "Min Gas" to "Safety Reserve" which is, probably, a better name for it. Many of the suggestions are quite good -- but others might tend to make this more like Lamont's paper (from which so much of this was cribbed). The idea is for this to be a cheat sheet (or outline thereof for someone with different tanks) -- a one pager that could be kept in the log book or whereever

As I wrote, keep the comments flowing.

BTW, DivingPrincessE -- you don't need to be "good with numbers" to do simple dive planning. But I think it would be a good idea to be able to do some simple dive planning!