Another Tables vs. Computers Thread

[TheRedHead]

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)

I would probably get more BT with my computer in gauge mode. I'm interested in the Suunto algorithm and why it does what it does at depth. The tables I have are all compartment oriented. Do you guys every think about you compartments when you dive? I know this sounds weird but I think about them like I have 16 boxes filling and emptying and what's going on with them.

Cozumel requires DMs for all dives except shallow shore dives. It's a Marine Park rule. The wrecks in Florida don't require DMs, but for some divers they should. :lol:

 

[limeyx]

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.

well, I hope you dont think I'm picking on you cause I'm not (well, except if you said you planned significant deco dives on a single tank ...) I'm just amused that we got this far and all seem to be mostly in agreement!

 

[limeyx]

I would probably get more BT with my computer in gauge mode. I'm interested in the Suunto algorithm and why it does what it does at depth. The tables I have are all compartment oriented. Do you guys every think about you compartments when you dive? I know this sounds weird but I think about them like I have 16 boxes filling and emptying and what's going on with them.

Cozumel requires DMs for all dives except shallow shore dives. It's a Marine Park rule. The wrecks in Florida don't require DMs, but for some divers they should. :lol:

The only mental reference to compartments I think about are "fast" and "long" tissues.

Generally if I do a deep dive, then I'm dominated by the faster tissues, so I better make sure I get the deep portion of the deco right. This means If I screw up and need to cut deco, I will cut the shallow deco. This is for dives probably of bottom times around 30 mins or less up to 160 feet. In theory if i get the deep deco correct (70 and 60 feet on 50% nitrox) then if I need to get out early, I am hoping to avoid a type II hit.

For shallower longer dives, it's more the long tissues and the shallower deco is more important, so I'm more likely to focus less on the deeper deco (which is why I might blow off the 50 and 40 foot stops on a 100 foot dive if we have a problem)

The GUE way is to try to keep things as idiot proof as possible in the water, and avoid calculations where you can (which is why MOD and not gas mixture is marked on stages etc.). Our instructor had a very valuable saying that all the research and theory is good, but it doesn't help you unless you can translate it into something relevant in the water.

Just like Charlie's "equivalent surface minutes" -- I dont use that method but I can see it's immediatlely helpful for planning dives -- it takes SAC which is not directly usable in the water and relates it to time (which I kind of do in my head) which *is* useful,or you relate time to PSI or whatever.

In the end, it doesn't matter so much what you do -- there is more than one way to do it (uck -- now I've gone and said it but sometimes there's value in a group of people picking a common way even if there are others that work too. Just like the standard gases -- if we do a 100 foot dive, I can be pretty sure most people will show up with 32% nitrox. For a 150 almost certainly 21/35 -- just makes things easier.

 

[Kevrumbo]

Lamont had a better Treatise on Rock Bottom/Gas Planning:
http://www.scubaboard.com/showpost.php?p=735077&postcount=33
http://www.scubaboard.com/showpost.php?p=735083&postcount=34
See also:
http://www.breakthrudiving.com/pdfs/battlefieldcalc.pdf
http://www.scubaboard.com/showpost.php?p=1640508&postcount=61

 

[boomx5]

What happens though in a true multilevel dive, such as when one pops down a wall, then spends the entire dive slowly ascend back up. Is depth averaging applicable to planning such a dive?

We regularly do shore dives where it takes up to 30-45 minutes to get to max depth. We did one a couple of months ago where it took 45 minutes to get to 220', made the switch off our stage to our back gas, spent about 15 minutes at around the 200'-220' range and then made our way home. Max depth 220', average depth was 150' for 60 minutes which gave us about 60 minutes of deco. These are long shore dives on scooters with a sloping bottom. Which means we have to come back up the way we went out. Depth averaging is perfect for these dive. It's funny, after down loading the profile from the D3 our calculations were right on the money. There are others who are doing dives that are more extreme than this within the same set of rules that we apply.

 

[TSandM]

You know, this discussion about wandering upslope to get to a depth where you have a smaller "rock bottom" is something I asked about during Fundies. I kept asking the question, and kept not understanding the answer, until Steve got irritated and pointed out to me that rock bottom is calculated for a direct ascent allowing all necessary stops. That's the quickest, most efficient trip to the surface, and rock bottom is the minimum gas that will get two of you there that way. Thus, it really isn't possible to swim up to a depth where you can stay longer IF you hit rock bottom at the depth where you are. Obviously, if you are ABOVE rock bottom, you can swim up to a depth where rock bottom is smaller and stay longer. But if you hit rock bottom, you go up; that's the only option at that point.

 

[Kevrumbo]

You know, this discussion about wandering upslope to get to a depth where you have a smaller "rock bottom" is something I asked about during Fundies. I kept asking the question, and kept not understanding the answer, until Steve got irritated and pointed out to me that rock bottom is calculated for a direct ascent allowing all necessary stops. That's the quickest, most efficient trip to the surface, and rock bottom is the minimum gas that will get two of you there that way. Thus, it really isn't possible to swim up to a depth where you can stay longer IF you hit rock bottom at the depth where you are. Obviously, if you are ABOVE rock bottom, you can swim up to a depth where rock bottom is smaller and stay longer. But if you hit rock bottom, you go up; that's the only option at that point.

Yeah it would be prudent just to start your ascent to the surface in normal non-emergency contingency, recreational diving. Ascending to and coming up against the next Rock Bottom value affords me only a few minutes at that depth --essentially the remainder of the dive becomes an elongated ascent profile.

As for Tables vs. Computers --if y'all have money to burn, utilize the NAUI RGBM Deco Tables AND carry along as back-up, the HS Explorer Dive Computer with a full-up RGBM algorithm/expression. . .

 

[Soggy]

That's the quickest, most efficient trip to the surface, and rock bottom is the minimum gas that will get two of you there that way. Thus, it really isn't possible to swim up to a depth where you can stay longer IF you hit rock bottom at the depth where you are. Obviously, if you are ABOVE rock bottom, you can swim up to a depth where rock bottom is smaller and stay longer. But if you hit rock bottom, you go up; that's the only option at that point.

That's not entirely true. While I would suggest that it's akin to riding the zero on a computer, you can get a new rock bottom if you ascend without issue. Consider that rock bottom includes the minimum amount of gas to get *two* divers to the surface from that depth including all stops. If you calculated a rock bottom at 130' and make it to 80' without any problems, you could conceivably spend a little bit of time at 80' before you reached the 80' rock bottom. Of course, this really only applies to NDL dives.

 

[limeyx]

You know, this discussion about wandering upslope to get to a depth where you have a smaller "rock bottom" is something I asked about during Fundies. I kept asking the question, and kept not understanding the answer, until Steve got irritated and pointed out to me that rock bottom is calculated for a direct ascent allowing all necessary stops. That's the quickest, most efficient trip to the surface, and rock bottom is the minimum gas that will get two of you there that way. Thus, it really isn't possible to swim up to a depth where you can stay longer IF you hit rock bottom at the depth where you are. Obviously, if you are ABOVE rock bottom, you can swim up to a depth where rock bottom is smaller and stay longer. But if you hit rock bottom, you go up; that's the only option at that point.

But you have to be somewhat careful if you want to adjust your RB "on the fly"
Rock bottom for a dive to 50 feet is not the same as RB for a dive where you were at 100 and have now moved up to 50 feet.

This is because in case 1, you do a 20, 10 stop (maybe a 30) but in case 2 you do the deco for a deeper dive (say average 80 feet) -- true, it's only a minute in this case (stop at 40) but it is a little different.

 

[Thalassamania]

But you have to be somewhat careful if you want to adjust your RB "on the fly"
Rock bottom for a dive to 50 feet is not the same as RB for a dive where you were at 100 and have now moved up to 50 feet.

This is because in case 1, you do a 20, 10 stop (maybe a 30) but in case 2 you do the deco for a deeper dive (say average 80 feet) -- true, it's only a minute in this case (stop at 40) but it is a little different.

You only get a signicant change in bingo air (rock-bottom as you call it) as you comnplete planned stops. The gain as a result of a single diver vs. two during the ascent just isn't that much, even coming up from 200 to a deep stop at 100, your buddy only contributes about 5 cubes to bingo.