Another Tables vs. Computers Thread

[TheRedHead]

You still aren't providing any details of how you actually do the planning though.
Saying I had 3400 psi to start and 2000 when I left the bottom is kind of vague.

and how do you adjust depth according to gas supply? inquiring minds want to know!

It's extremely simple. I have rock bottoms memorized and I'm constantly aware of my depth and gas. You are diving with a group. There is 150+ feet of viz and a boat is following you. If you are close to your rock bottom, you ascend 20-30 feet and you're still with the group below. Generally (except for the odd example I gave) we are diving multilevel from deep to shallow so rock bottom is fluid as we ascend. In most situations, I run up against NDL before rock bottom so I ascend anyway. I can't recall running up against rock bottom on air dives. Most of the 2nd dives are usually 50-60 feet on Nitrox.

 

[minnesota01r6]

Are you ascending to minimize gas consumption, or ascending to a depth where you are still within rick bottom? If you have to descend 30' to get to your buddy, you may be beyond rock bottom. Or are you having your buddy ascend with you?

 

[Charlie99]

If the profile is too variable to predict from the surface and you rely on a computer in the water, what happens if you ascent to 30 feet and it says you have 10 mins of deco left? and then at 20 you have 20 mins? how do you know in advance that you wont be in that situation?

Come on now. Think about it a bit and you'll realize that will NEVER happen. What will happen is that you have 3 minutes at 10' required deco when at 80', and it goes away during a slow ascent with1 or 2 minutes stops at 40' and 30'.

and how do you adjust depth according to gas supply? inquiring minds want to know!

My rock bottom formula for an AL80 is ultra simple --- 100psi per 10', but never less than 700. As was discussed in the 3 year old thread, Rock Bottom Air Reserve for Ascent from 100', 100psi/10' comes out pretty close to the requirement for either a direct ascent with a panicked buddy, or a normal ascent with deep stops.

Drift dives are a special case for gas planning since you only need to have, at any point in the dive, sufficient gas to get you and your buddy to the surface. As a lazy guy, I love drift diving with its valet pickup service.

 

[TheRedHead]

Are you ascending to minimize gas consumption, or ascending to a depth where you are still within rick bottom? If you have to descend 30' to get to your buddy, you may be beyond rock bottom. Or are you having your buddy ascend with you?

If you ascend from 100 to 70 feet you both decrease your gas consumption and rock bottom. Say rock bottom is 1500 at 100 feet and 1000 at 70 feet. At 1600 psi you move up to 70 feet and are now using less air and approaching the new rock botton more slowly. It works very well.

I dive with my buddy even in a group and we stick together and operate as a close buddy team. It's usually a case of NDL before rock bottom when diving air with large tanks.

 

[TheRedHead]

My rock bottom formula for an AL80 is ultra simple --- 100psi per 10', but never less than 700. As was discussed in the 3 year old thread, Rock Bottom Air Reserve for Ascent from 100', 100psi/10' comes out pretty close to the requirement for either a direct ascent with a panicked buddy, or a normal ascent with deep stops.

Thanks for link, Charlie. I love drift diving too. It's easy diving that doesn't require minute detail in planning.

 

[lamont]

i go away for three days, and 100 posts later the topic has changed to rock bottom...

for Al80s I like (depth in ft * 10) + 300 psi for rock bottom down to 100 fsw better, for E8-130s i like straight (depth in ft * 10). then even if you're excited you can still hit your stops (my SAC rate was 1.1 cu ft / min averaged over an entire dive when i was a newbie without being in a panic), and you've also got some padding in case it takes longer than you expect to sort out a cluster at depth.

 

[limeyx]

Come on now. Think about it a bit and you'll realize that will NEVER happen. What will happen is that you have 3 minutes at 10' required deco when at 80', and it goes away during a slow ascent with1 or 2 minutes stops at 40' and 30'.

My rock bottom formula for an AL80 is ultra simple --- 100psi per 10', but never less than 700. As was discussed in the 3 year old thread, Rock Bottom Air Reserve for Ascent from 100', 100psi/10' comes out pretty close to the requirement for either a direct ascent with a panicked buddy, or a normal ascent with deep stops.

Drift dives are a special case for gas planning since you only need to have, at any point in the dive, sufficient gas to get you and your buddy to the surface. As a lazy guy, I love drift diving with its valet pickup service.

If you overstay a 120 foot wreck for 5-10 mins it could.

I am a little more conservative on my RB as my SAC is somewhat higher than you guys (although SAC doesn't affect too much RB as I plan on 1.0 SAC for RB anyway)

 

[limeyx]

Thanks for link, Charlie. I love drift diving too. It's easy diving that doesn't require minute detail in planning.

Most of my diving doesn't require minute detail either
I dont think it ever takes more than 3 mins to plan a rec or a tech dive (unless we are diving together for the first time)

 

[limeyx]

It's extremely simple. I have rock bottoms memorized and I'm constantly aware of my depth and gas. You are diving with a group. There is 150+ feet of viz and a boat is following you. If you are close to your rock bottom, you ascend 20-30 feet and you're still with the group below. Generally (except for the odd example I gave) we are diving multilevel from deep to shallow so rock bottom is fluid as we ascend. In most situations, I run up against NDL before rock bottom so I ascend anyway. I can't recall running up against rock bottom on air dives. Most of the 2nd dives are usually 50-60 feet on Nitrox.

Amusing almost the exact same way I dive, except my computer is in gauge mode, and I'm keeping a running weighted average depth to gauge how much time I have left and whether or not I need to start ascending.

(oh and I get the feeling you have to dive with a DM -- whereas that's not the way it works here, so we are more likely to do an out and back dive as standard. Not much drift diving here)

 

[TheRedHead]

I'm not going to say what my RB numbers are because I'm tired of being picked on.

I'm a super planner of tech dives because I haven't done it enough tech dives to feel comfortable. I always have a plan, a too deep plan and a too long plan.