Questions about Rock Bottom Gas PLanning, Fundies

[DIR-Atlanta]

But, DIR-Atlanta, wouldn't you agree that an actual calculated RB should be based on an actual SAC rate known for both (or all three) team members?

Absolutely, which is why it is important for each team member to know both their resting and working SAC rates. However, for classroom purposes, they have to assume some baseline value to demonstrate the concepts and calculations. Ideally, students should take the class example and fine tune it to the particular SAC rates that are appropriate to their own personal consumption as well as their team's.

The point that I was trying to make is that the Rock Bottom calculation is more than just a "magic number". It is a heuristic that can (and should!) be applied to the individual requirements of a specific diver and his or her team.

 

[H2Andy]

to the extent that rock bottom is a model that approximates (but never equals)
real-life gas usage under certain circumstances, i would agree

you could never have rock bottom EQUAL reality because there are simply too
many variables. in other words, it's a prediction based on past experience
modeled on a series of premises also based on past experience of what
factors should determine how much of a reserve you should have

but you CAN get close enough for it to work

 

[Jason B]

in the meantime, you can use GUE's "rule of thumb" rock bottoms for an AL80

for dives to 60 feet, your rock bottom is 700 psi
for dives from 60 feet to 100 feet, your rock bottom is 1000 psi

that means you should begin your ascent to the extraction point
when you hit rock bottom

plan the dive so you hit rock bottom close to the extraction point.

The Student Workbook calls these "Standard single tank rock bottoms".

 

[BCS]

I agree, but the concept of rock bottom isn't rocket science and even a mediocre understanding of it is better than none at all until scubamikey can get more training.

Actually, getting the answer from an Instructor is better than any of it.
And although it's not rocket science, it does get butchered o n the boards (like most of these concepts)If it were so simple then we would see one post explaining it and not 20+ all w/a bit different take.
Just trying to make sure the student gets the real answer and not someone's opinion who may or may not have even taken the course or even have any experience diving.
Too often it's taken as an absolute and the concept is then lost. Nothing is absolute and definitely not in gas planning, as conditions/objectives change, so does the need to accomodate emergency gas planning.
Explaining this concept on the Net almost always yields the same result. That is the questioner is either a) confused, or b) given the wrong answer and believe it to be correct. This comes from experience teaching DIRF....and the battle to overcome info gleaned from the Net (or misinfo).
Discussions are great, but teaching on the Net is tough and often leaves a lot out of the answer.
This is all my own humble opinion and given only in an effort to ensure that the person who originally asked the question was aware that he/she could get the guaranteed correct answer w/a simple e-mail to soemone w/credentials to teach the subject.

Safe Dives!

Best Regards,
brando

 

[caverdave]

New diver here, trying to go DIR. No dives since OW class. I really felt that there was more to learn than the SSI books told me, so I bought and read JJ's book "Fundamentals of DIR", and the "Dress for Success" book. I like what I read. Obviously Fundies is tought as a class, can someone list the outline or just give me an idea of what is taught? I suspect that I should get a little OW experience before taking the class, to really be able to appreciate it?

Hopefully you haven't been too baffled by all the posts!

I usually don't write but feel as if I was in your shoes about a year ago (had just finished OW and felt that there was a whole lot to go, wasn't getting what I felt to be good answers from the LDS, read the book started to wonder etc). I'd encourage you to contact one of the instructors and to particularly look into taking the class.

The GUE instructors I had were very open to a huge amount of questioning from me before, during and after the class. The books are good, but they only scratch the surface.

I think my class was taken at about 20'ish open water dives, maybe it is possible to take it "too early" after OW, but I suspect that it is not.

Good Luck!

Dave

 

[neophyte]

Actually, getting the answer from an Instructor is better than any of it.

Discussions are great, but teaching on the Net is tough and often leaves a lot out of the answer.
This is all my own humble opinion and given only in an effort to ensure that the person who originally asked the question was aware that he/she could get the guaranteed correct answer w/a simple e-mail to soemone w/credentials to teach the subject.

Safe Dives!

Best Regards,
brando

It looks to me like someone w/ credentials to teach the subject is offering you a guaranteed correct anwer if you send him an email.

Having been DIR-Fed by BCS and MHK just last weekend on Catalina Island, I'd suggest you take him up on (what reads to me as) his very generous offer.

That's my humble opinion,

Adam

Oh yeah, WOW! what a class...

 

[Ben_ca]

It looks to me like someone w/ credentials to teach the subject is offering you a guaranteed correct anwer if you send him an email.

Having been DIR-Fed by BCS and MHK just last weekend on Catalina Island, I'd suggest you take him up on (what reads to me as) his very generous offer.

That's my humble opinion,

Adam

Oh yeah, WOW! what a class...

Where's the write up? Class report?