Gas/Depth planning: am I a horrible diver?

[NudeDiver]

From another thread...

One way or the other, I do need to be able to calculate my SAC and at a minimum, know how long I can last on a specific amount of gas at a specific depth.

Now, what I am about to ask is NOT about SAC rates or being able to calculate them. Please don't answer that question here. There are other threads for such things

My question is more about knowing the dive site and what to do about it (if anything).

We have two sites I go to - pretty much the only two sites I go to (one of them much more than the other). I have some idea of what's down there - and what it's like. For the primary site, a very crude map is available. When I go to these places (shore dives) with my buddy, we really do not plan much of anything. Yeah, we talk about whatever, yeah, we'll do buddy checks, yeah, we might go over a few signals and agree at what point we should turn back (generally at a half tank) and what the signal is - and we MIGHT say, "let's not go below X depth." But that's it. Navigation isn't a big deal either. Down slope is deeper, up slope is shallower. If you're going deeper, you know that shore is the other way - even if you can't see the bottom. Nothing too complicated about that.

We never sit down and go, "OK, we'll go to to X depth for Y time, and then go to A depth for B time" or whatever. Frankly, we just go down there and look around until it's time to turn back. Our dives are not so complicated that it seems like SAC rate would be an issue, in terms of using them to plan the dive in some way - since we don't really know how deep we're going to end up going anyway. 25m would be a deep dive for us, 18 or 20m would be more typical. We're conservative enough that even if we were at 25m and burning air faster than normal, it would not be a big deal to just go to the surface and swim back to shore if we really had to. Unpleasant, sure, but not a big deal. FWIW, as far as I can remember, we only had to do that once and it seems like it had something to do with something other than air consumption.

As an added twist - and PLEASE don't let this bring out the "anti-air-integrated crowd" and related comments - please - please - please (I know the arguments already, thanks) - if we are both using AI computers and using the "estimated time based on actual consumption" as a GUIDE (again, I know the issues, thanks), in addition to the NDL and in addition to the actual tank reading - doesn't SAC and depth planning take on MUCH less significance in the scenario that I've provided? Not any other scenario (I'm looking at YOU J.R.)...this one.

Anyway - I know I have asked the "how much planning do you need?" question before, but it wasn't in these terms (concerning SAC and gm issues), so here it is again.

 

[Teamcasa]

Like I also said in that post, "Gas planning or management is very much gear configuration, dive buddy and dive site dependant."

When my wife and I dive the Casino Dive Park frequently, we don't do any dive or gas planning. We both know the site well and we also know that IÃÍl be low on gas before she is. We go in, have a great time and after 50-60minutes, we get out. She will still have +1000psi and I'll be down to 400-500psi.

I don't think a serious planning session is required for this type of diving but I also said, "Same goes for dive where exiting whenever I want is not an option. Cave, deep wrecks or some caverns will also dictate that I know not just my dive plan but I need a complete understanding of my buddy's plan as well."
- These dives mandate a real dive plan and gas planning.

 

[gcbryan]

To me the question is not how much planning you need to do for a particular site but more do you understand how to do it. If you understand how to do it you understand the factors involved and you can either decide to use them or not on a particular dive.

For instance, if you figure out "rockbottom" for both of those dive sites you never have to do it again but it's good to know how much gas you would need if something happened at the deepest part of your dive and you had to get you and you buddy to the surface. It's better if you thought about it before using some realistic numbers instead of just guessing or hoping.

That's my take on it.

 

[Slonda828]

Nude,

I think from speaking to you on here that you have a pretty good grasp on what you are doing. I find that when I dive at a site I've dove a million times (like you in this instance), then I don't really gas plan. If I'm diving the springs, I dive until I have 500 PSI left, then go to 15 feet, hang out, and tinker around until I have 250-300 PSI left (sometimes less), then pop up. If I'm ocean diving I take it a lot more seriously and plan routes and turn pressures and rock bottom and such. It's like the difference between a day hike and a week long backpacking trip, you know? If I'm day hiking I throw some granola bars and a bottle of water in my pack. If I'm going for a week then I weigh all my food to the ounce. I don't think anyone besides a bunch of bored scubaboarders would Monday morning quarterback you on your relaxed gas planning on a familiar site, and even if they do, who cares. If the government was run by half the people on here, we'd all be wearing football helmets to work and our cars would be covered in foam.

 

[Charlie99]

You need to do the planning required for the dive.

A couple of key items to your frequent dive site are
1) "it would not be a big deal to just go to the surface and swim back to shore". In other words, to safely abort a dive, you only need enough air to get you and your buddy to the surface. and
2) "25m would be a deep dive for us, 18 or 20m would be more typical" means that your NDL times are relatively long, and it would take both of you being inobservant for quite a while for you to rack up a mandatory deco obligation.

With those two conditions, only a bare minimum of dive planning is needed.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

At the end of my PADI OW cert course I asked the instructor about dive planning. He passed on a couple simple rules that have worked well for me:

1. If you start back towards shore at 1/2 tank, then you'll have enough air provided you either head back more directly, or you stay more shallow on the way back in.

2. Never go below 100psi per 10' of depth. Add a bit more margin for your first couple dozen of dives as you'll be breathing air faster.

Since then I've done all sorts of complicated calculations on rock bottom, but the results for an AL80 aren't materially different than 100psi per 10' or perhaps 100psi/10' + 300psi extra.

Charlie Allen

 

[Puffer Fish]

I do an awful lot of divers that involve... going down the bottom... and calling the dive whenever I see the last person head up the anchor line...

I have this thing about being the last person back on a boat... as it seems they are the only ones that get left behind...

So, even if I don't directly go up... I at least go to the anchor line... so they cannot leave.

Dives off of Destin/Panama City tend to be between 100 and 60 ft.. and with the tanks I normally dive with...using NITROX..I come back with a giant safety margin.

In south florida, I'm the one with the big SAC rate... and with drift diving...just dive to a pressure and head up...

Only about 10 dives a year are planned in any form..

 

[TSandM]

We have a local dive site with a max depth of about 35 feet. When I dive there, I'm not worried about rock bottom, because it's less than the minimum amount I'm willing to get to in a tank, anyway. All I'm worried about there is what our route is going to be, and to make sure we turn back early enough so that everybody has enough gas to get back to shore underwater (because I hate surface swimming). So gas planning consists of identifying everybody's turn pressure.

We have another site where you can do a traverse from one entry point to another. The route goes fairly deep, running about 100 feet for ten or fifteen minutes (depending on how fast you swim, and what you find to look at). The first time I did that dive, I sat down with my buddy and we calculated our respective gas consumption, the expected times at various depths, looked at our NDL limits and our rock bottom for several selected points on the dive, and made sure we each were carrying enough gas to complete the dive safely. Rock bottom on this dive was worth thinking about!

Two different scenarios, two different degrees of planning. And the other thing is that we have DONE the planning . . . I know what rock bottom for 60 and 100 feet is for each of the tanks I use, and so do my buddies, so we don't have to go through that formally for each dive. But on the ones that have surfacing constraints or are more aggressive or unfamiliar, we'll still quickly run the numbers.

 

[Dave1234]

Football helmets and car's wrapped in foam
Like it

 

[Bill_PNW_Diver]

I wouldn't say your being irresponsible but the thing you need to ask yourself is.....

At my maximum depth would I have enough gas to get me and my buddy to the surface safely in a stressful out of air situation?

If you sit down and do the math you may be surprised at just how much gas you and a buddy would consume during a stressful OOA incident.

Here's a great article from Bob (aka Greatfuldiver) that explains gas management:

NWGratefulDiver.com

As for me I know what my and my buddies rock bottom is for each tank we dive and for depths between 60ft and 110 ft. For the common divesites we dive I do the same pre-dive planning that you do except our first turn around pressure is determined by rock bottom.

 

[ShakaZulu]

It's all about experience: unfortunately in the school of life, you have the experience first and then learn the lesson. In diving, failing the test, could mean your death....best you have a basic idea of what you are doing when you first start out.