Multi Level Dive Logging?

[Todd Whitworth]

My computer does have download capabilities, but the cord to connect it to my laptop was not included with the computer. It was a significant extra expense to get the cord, so I skipped it. Dive kit is expensive enough as it is.

Todd

If you use a dive computer with download capability, download it to the software that came with it, or use "Subsurface" and it will show the profile for multi-level depths you made during the dive with resolution that correlates to the sampling rate you have in the computer.

NOTE: It is either dive computer or dive tables on the same dive/dive day not both. You really can't/shouldn't try to extrapolate from one to the other. If you are going to switch using one from the other, you will have to wait 24 hours without diving to switch to the other.

 

[Steve_C]

Max depth is one item: I have had occassion where the dive op wanted X logged dives to at least Y fsw within the last Z years. Typically Y was 80 and once or twice it was 100. Z was usually 1 or 2. This was a requirement in place of AOW since you can get that with only 65 ft or so.

Length of dive is another.

A more important factor than all the levels is the type of dive. Drift, night, boat, low viz, cold, etc. That might be relevant when going for DM if instructor wanted to verify you had the required experience. Had that happen with both DM and MD since I did them with multiple agencies.

Also the temperature, your configuration, fresh or salt, tanks., etc. including the weighting if correct. By the time I got to DM I had dove fresh and salt, shorty, dive skin, 3mm, 5mm, 7 mm, 10/14 for wet suits plus dry suit. For tanks there were AS80s, high density Al80s, LP95s, HP100s, AL100s, Al120s, and a couple of others. If you dive when you travel it is very good to keep all those weights written down.

 

[Todd Whitworth]

I have my gear/weights written down for every dive. Need to include the weight of the tank, thanks for reminding me.

Cheers,

Todd

Max depth is one item: I have had occassion where the dive op wanted X logged dives to at least Y fsw within the last Z years. Typically Y was 80 and once or twice it was 100. Z was usually 1 or 2. This was a requirement in place of AOW since you can get that with only 65 ft or so.

Length of dive is another.

A more important factor than all the levels is the type of dive. Drift, night, boat, low viz, cold, etc. That might be relevant when going for DM if instructor wanted to verify you had the required experience. Had that happen with both DM and MD since I did them with multiple agencies.

Also the temperature, your configuration, fresh or salt, tanks., etc. including the weighting if correct. By the time I got to DM I had dove fresh and salt, shorty, dive skin, 3mm, 5mm, 7 mm, 10/14 for wet suits plus dry suit. For tanks there were AS80s, high density Al80s, LP95s, HP100s, AL100s, Al120s, and a couple of others. If you dive when you travel it is very good to keep all those weights written down.

 

[TMHeimer]

I think it's all been said, but I will add that tables are only really good if you do a square profile--ie., staying right near the bottom at your deepest depth. Otherwise, your tables will most likely say you are over the NDL limit.
My first dive after OW cert. was to 54', but I was only there for maybe 3 minutes. The rest of the time at 20 feet. My tables said I should be dead.
The odd time I use my computer an a truly multi-level dive I just leave the pressure "box" on my log empty and note it was a computer multi level dive.

 

[Todd Whitworth]

Thanks, looking at the average depth makes sense and the computer provides that for me. Appreciate the help!

Todd

average depth.

 

[Jim Lapenta]

You can track multi-level dives using a computer or bottom timer and tables but, it requires a serious commitment to details. In addition to planning the dive carefully and sticking with that plan. You basically plan the dive as a series of steps. Say 10 minutes at 60ft, up to 20 minutes at 40ft, then finish it up with say another 20 at 20 ft. You figure the pressure groups for each stage of the dive using tables, or if you can find one - a PADI Wheel or ERDPML- and follow the steps to do so.

Some recreational divers find this too restricting as when you plan the dive as a multilevel, you don't deviate from the plan. Sawtoothing and bouncing between depths will throw your numbers off. What does happen if you really get into this and stick with it is you learn a valuable sense of discipline that too many divers and dive pro's don't have. The example I use when teaching dive planning and sticking to the plan is a bar of gold.

We plan a dive on a wreck or over a reef at 100 ft. The plan is going ok until you look down towards the end of the dive and see a gold bar in a hold at 120. You go after it and grab it. Take the time to secure it and start to swim up. Problem is that this little detour has now put you in a decompression situation and possibly risked the safety of the team.

So you get to the surface, you have the gold, and maybe you don't care but I will never dive with you again due to your lack of discipline and sound judgment.
What should have happened is the bar should have been the objective for the next dive.

 

[stuartv]

Thanks, looking at the average depth makes sense and the computer provides that for me. Appreciate the help!

Todd

Average depth is useful for calculating gas usage. It is USELESS for determining inert gas tissue loading (and thus, table-based Pressure Groups).

There is a lot of discussion of algorithms, including some for using average depth for manually calculating decompression obligations. Those discussions are in other subforums and, in my opinion, are not appropriate to even bring up here in the Basic forum.

For purposes of your original question, AVERAGE DEPTH IS USELESS.

If you're going to use tables, stick to your training and base things on the maximum depth reached during the dive.

If you're just calculating a PG in order to record it in your log for historical purposes, don't bother. Nobody down the road is ever going to look at or care about that.

If you're actually going to use a PG to calculate your NDL for a second (or subsequent) dive, then, as has already been noted, you need to use table-based planning for your first dive and follow what it says (i.e. adhere to the table-based NDL, even though your computer would let you stay down longer).

Your best bet is to simply learn how to use the planning function in your dive computer to plan your dives. Dive planning using tables will really limit your bottom time - especially if you are normally doing multi-level dives. If your dive computer doesn't have a planning function, it might be time to think about getting a more fully-featured dive computer.

 

[JackD342]

Yeah, when I first got my own gear, computer included, I continued to log my dives and calculate pressure groups for a while. (but not multi-level) I eventually realized that was pointless with one exception: if the computer had crapped out on me and I had not exceeded my RDP NDL limits, I would have been able to pick up right where I left off, using analog gauges. But once I started diving profiles that a computer allows but the RDP doesn't, why bother?

With PADI it is the eRDPml that allows you to plan and execute multi-level dives; but as has already been pointed out, sticking to that plans requires a significant level of discipline.

 

[Todd Whitworth]

I just started diving with a new buddy, and on our last 2 dives (4 days apart), we went to about 80 or 90ft max. We adhered to the limits of the computer and stuck to our dive plan. Both of us had one tank and therefore only did one dive. Where I got tripped up, prompting me to ask the original question was my ending pressure group. How do I figure that out? I wasn't at 80ft for very long, but my training tells me that I need to 'act as if" I was at 80ft for the whole dive. When I tried that with my RDP at home I found I was well over the table limits for DCI, but I was only at 80ft for a few minutes and began to slowly ascend and finish the dive much shallower. So I didn't understand what to do with my data.

I don't dive that deep very often, I'm usually around the 40' - 60' mark for most of the dive, and that's much easier for me to calculate, but I wanted to challenge myself safely, and I was comfortable as I was diving with an individual with a lot more experience than I who has good practices when it comes to saftey.

Does that make sense?


Todd

 

[JackD342]

Maybe this will help - I have tried to provide a visual representation for this in the past.

First, no matter what algorithm or planning tool you are using, a dive profile does not become any more or any less safe based on the planning/tracking tool used. You are still experiencing the same dive.
Think of using a computer, versus an eRDPml, versus the RDP, as moving through a progression of reduction of "rounding errors" that are inherently designed to err on the side of caution.

In this diagram, the "square profile" of an RDP counts the whole of the square area "against" you. As you use different devices, you start reducing that area, allowing for more liberal NDL times and depths.