Questions about Rock Bottom Gas PLanning, Fundies

[scubamikey]

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?

Next question. Whenever the DM said "end the dive with 500psi in your tank" I thought, "well, how do I do that?". Sounded like a good way to run out of air. Luckily I found out about Rock Bottom Gas Planning. I read the charts and I understand the calculations (2 divers need to ascend, elevated SAC rates, do the safety stop, and still end up will 500psi left). Am I missing anything?

It's my understanding that as long as I begin my ascent before I reach my NDL or Rock Bottom psi (whichever I hit first), that I will maximize my bottom time and still be safe. Did I miss anything? I intend to do a lot of shallow (under 60', lots at 30') diving on air, so the NDL will be large and I think the Rock Bottom limits will indicate when I need to end the dive.

 

[BCS]

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?

Next question. Whenever the DM said "end the dive with 500psi in your tank" I thought, "well, how do I do that?". Sounded like a good way to run out of air. Luckily I found out about Rock Bottom Gas Planning. I read the charts and I understand the calculations (2 divers need to ascend, elevated SAC rates, do the safety stop, and still end up will 500psi left). Am I missing anything?

It's my understanding that as long as I begin my ascent before I reach my NDL or Rock Bottom psi (whichever I hit first), that I will maximize my bottom time and still be safe. Did I miss anything? I intend to do a lot of shallow (under 60', lots at 30') diving on air, so the NDL will be large and I think the Rock Bottom limits will indicate when I need to end the dive.

Hi ScubaMikey,
You can find the course outline on the GUE website (www.gue.com) and that will give you a good idea of what is covered. But my advice is to get your answer directly from a GUE Instructor. Bob Sherwood at "All About Scuba" and/or Dan MacKay at "Northern Tech Diver" are both in that neck of the woods, are great instructors, and are always happy to answer questions. You can find thier resumes, links to e-mail addresses, and thier website addresses on the GUE website.
Good luck and dive safe!

Best Regards,
brandon

 

[Soggy]

Also a quick search on scubaboard for "rock bottom", "mgr", or "minimum gas reserve" should bring up a bazillion threads with the concept explained.

 

[BCS]

Also a quick search on scubaboard for "rock bottom", "mgr", or "minimum gas reserve" should bring up a bazillion threads with the concept explained.

Sog,
The only problem w/that method is that one has to try to discern who is giving the correct answer and also they have to weed through all the bickering.
Simple route and guaranteed correct is to contact a GUE Instructor.
It's difficult to teach via the Internet....it leaves a lot of room for misinterpretation.
I know this from getting Fundies students who've learned this stuff viathe boards only to have to "unlearn" it in class so they get it right.
Hope all's been well w/you and you're getting in more diving time than forum time!!!

Best Regards,
brando

 

[Rick Inman]

New diver here, trying to go DIR. No dives since OW class. .

IMO, you are actually in a good position to take the fundies class, before you form and have to break the bad habits like I did (and still do). You'll want enough dives in to be comfortable underwater for the class to be effective. But the sooner you take it, the better.

 

[H2Andy]

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.

for example, assuming a dive to 100 feet with 3,000 psi starting pressure,
dive 1000 psi out, 1,000 psi back, and you now have hit rock bottom and begin your ascent. should your buddy go OOA at any point in the dive, you would
have had enough air to get you and your buddy safely to the surface.

 

[Soggy]

Sog,
The only problem w/that method is that one has to try to discern who is giving the correct answer and also they have to weed through all the bickering.

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.

Hope all's been well w/you and you're getting in more diving time than forum time!!!

The diving has been great, except we have 9-14 ft seas forecast for this weekend, so it's the pond or quarry this weekend.

 

[TSandM]

scubamikey, the bare bones of the Fundies course are outlined on the GUE website. For a fleshed out view of what the class is actually LIKE, try these links:

Rick's and my report

Mo2vation's reports: Part 1, Part 2, Part 3, and Part 4

SeaJay's report

Somewhere, recently (and I can't find it) there was a great discussion of RB values and rules of thumb . . . But the gist is that you can calculate RB for the tank you use and your (and buddy's) SAC rate for a number of depths and either memorize it, or record it on your wetnotes. It doesn't have to be precise (you don't have to calculate RB for a sixty-SEVEN foot dive -- just use 60 feet or 80, depending on how conservative you want to be) because nothing we do underwater is that precise. And remember that, if you are doing a terrain-based dive, your RB is relative to the depth where you are . . . If you have calculated RB at 1000 psi for your maximum depth, but you are now at 30 feet later in the dive, you don't have to go directly to the surface when you hit 1000 psi, as you would if you had done it at depth.

 

[DIR-Atlanta]

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

I know this may seem like nit-picking, but technically speaking, those are not really "rules of thumb". They are calculated values based on all the things that have been discussed so far in this thread (deal with emergency, safe ascent, min deco, etc for two people breathing off one tank). A "rule of thumb" would be something like "reserve 100 PSI per 10 feet of depth", which does not take any of that into account.

The only reason I'm bringing it up at all is to emphasize that this Rock Bottom stuff is all a part of appropriate dive planning. To me, using a "rule of thumb" implies that the team did not really plan things that well. A rule of thumb will probably work in most cases most of the time, but I think it's better to actually plan things so that you know you will have adequate gas reserves - and that's what Rock Bottom is really all about.

 

[TSandM]

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? By that criterion, any published "rule" is a rule of thumb.

I dove with somebody last week for whom the 700 would be gross underestimation, whereas if NW Grateful Diver and I were diving together, it would be absolutely ample.