Anyone want to run a few simulations for me?

[O2BBubbleFree]

(Extracted from another thread)

I’m considering a contingency plan in case my computer ever dies during a dive, and would like to have people test it in whatever dive software they have.

A little setup: I am a strictly no-deco, no-overhead, don’t-push-the-limits, diver. I use a computer, but so far can’t justify buying a back-up. If my comp dies and I have to abort a dive and sit out the rest of the day, I’m fine with that. I realize that there are lots of reasons dives could get canceled, and computer failure is pretty low on that list. I’ll be upset, but I don’t think the risk of it happening justifies the cost of a back-up computer.

However, I have been considering another contingency plan, but don’t have a simulator that I can test it on. If you have a dive planner that you could run some simulations on, please let me know the results.

Here’s the scenario: On the first dive of the day, the comp craps out after I have passed what would be the RDP NDL for the max depth. I immediately abort the dive, and since I am now cutting the dive short, I would have plenty of gas to make the most of my ascent (i.e. increased stops and/or times, based on your preferred ascent technique).

During the shallower portions of the multi-level dive I would have either been off-gassing or loading at a lower rate than at max depth. So, can I take the my max depth (actual) and use the max NDL for that depth (RDP), and plan the repetitive dive? The N2 value obtained should be greater than my actual N2 loading, cutting my next dive short, but with a healthy safety margin.

My instinct is that this would keep me well within the NDL of any multi-level dive. It may cut my second dive times considerably (compared to a back-up computer or other multi-level dive calculation method), but, again based on the low incidence of computer failures, I’m OK with that.

 

[miketsp]

Download a copy of the SDM = Suunto Dive Manager for free. It's a fairly conservative computer and you can run all the simulations you want. You don't need to have the computer to use SDM.
You should find it with Google.

 

[O2BBubbleFree]

Download a copy of the SDM = Suunto Dive Manager for free. It's a fairly conservative computer and you can run all the simulations you want. You don't need to have the computer to use SDM.
You should find it with Google.

Thanks!

 

[Scuba_Steve]

Call me a wild-man, but assuming you're doing only Rec, NDL dives, and again, assuming you check your gauges somewhat occassionally, what would be wrong with doing a normal ascent, 3min @ 15ft-ish and hop on the boat? I would assume you'd know your computer went in the bag within, say the last 2-3 minutes at most, maybe more.....you know what you last saw, do the math, and relax.

Why all the hoop-lah? and worry? Heck take 5 @ 15ft then for added safety.

I realize that Padi's "answer" for the above question assumes a whole pile of stupid, on the part of the diver, I however do not.

Call me optimistic (And possibly wrong!!)

Regards

 

[Jim Baldwin]

(Extracted from another thread)

I’m considering a contingency plan in case my computer ever dies during a dive, and would like to have people test it in whatever dive software they have.

A little setup: I am a strictly no-deco, no-overhead, don’t-push-the-limits, diver. I use a computer, but so far can’t justify buying a back-up. If my comp dies and I have to abort a dive and sit out the rest of the day, I’m fine with that. I realize that there are lots of reasons dives could get canceled, and computer failure is pretty low on that list. I’ll be upset, but I don’t think the risk of it happening justifies the cost of a back-up computer.

However, I have been considering another contingency plan, but don’t have a simulator that I can test it on. If you have a dive planner that you could run some simulations on, please let me know the results.

Here’s the scenario: On the first dive of the day, the comp craps out after I have passed what would be the RDP NDL for the max depth. I immediately abort the dive, and since I am now cutting the dive short, I would have plenty of gas to make the most of my ascent (i.e. increased stops and/or times, based on your preferred ascent technique).

During the shallower portions of the multi-level dive I would have either been off-gassing or loading at a lower rate than at max depth. So, can I take the my max depth (actual) and use the max NDL for that depth (RDP), and plan the repetitive dive? The N2 value obtained should be greater than my actual N2 loading, cutting my next dive short, but with a healthy safety margin.

My instinct is that this would keep me well within the NDL of any multi-level dive. It may cut my second dive times considerably (compared to a back-up computer or other multi-level dive calculation method), but, again based on the low incidence of computer failures, I’m OK with that.

I started diving 25 years ago with no computer, no BCD and no octopus. With that said computers and BCD's have made diving available to many people.and are truly great inventions. But they do not replace good old fashioned common sense.

I now own four computers, three BP&W's and a couple of BCD's. I made four trips to Cozumel last year. In addition I spent a week in Costa Rica along with a couple of trips to Florida and Arkansas.

I dive with one computer and a $35 Timex as a chronograph. I know my tables and if my computer died I wouldn't bat an eye. I always do more than the minimum 3 @15.
I may do 5 to 15 minutes of hang time depending on the profile.

Run your square profile on a table. You did a multilevel so you didn't stay at depth for the whole time. Figure your SI and plan your next dive.

I don't see the need or the expense for carrying two dive computers on a recreational dive. On technical dives I carry two dive comptuers along with two sets of run times/tables.

 

[O2BBubbleFree]

Call me a wild-man,

Wild-Man!

but assuming you're doing only Rec, NDL dives, and again, assuming you check your gauges somewhat occassionally,

Yes, those assumptions...

what would be wrong with doing a normal ascent, 3min @ 15ft-ish and hop on the boat?

Nothing. I left out the details because it's not germane to the question I apparently failed to ask. Plus, I didn't want to debate ascent techniques. Insert the technique of choice.

I would assume you'd know your computer went in the bag within, say the last 2-3 minutes at most, maybe more.....you know what you last saw, do the math, and relax.

Herein lies the rub. What math? I want to use the RDP to get max time for the repetitive dive, but what do I use for time/depth of the first dive? As I said, using the multi-level computer I exceeded the square-profile NDL of the RDP.

I realize that Padi's "answer" for the above question assumes a whole pile of stupid, on the part of the diver, I however do not.

Not sure what you mean here. Padi didn’t give me an answer, but maybe things have changed or I got short-changed. Care to expound on this?

 

[O2BBubbleFree]

Run your square profile on a table. You did a multilevel so you didn't stay at depth for the whole time. Figure your SI and plan your next dive.

That's my plan. Just looking for confirmation and ideas.

I don't see the need or the expense for carrying two dive computers on a recreational dive.

Nor do I.

OK, here's the rest of the story. On another thread I implied that if my computer died in the middle of a dive I would fall back to the tables to plan the second dive. Someone questioned whether that is possible. Rather than further hijack that thread, I launched this thread, and thought it best to do so in the form of a question. I was also hoping to get some real-number feedback that would give me a better feel for how much overkill this approach would be for various profiles. Now that I have the link to free planning software, I can get that info myself.

Thanks for your input.

 

[Scuba_Steve]

Hi 3dent, lets chat

Herein lies the rub. What math? I want to use the RDP to get max time for the repetitive dive, but what do I use for time/depth of the first dive? As I said, using the multi-level computer I exceeded the square-profile NDL of the RDP.

Not sure what you mean here. Padi didn’t give me an answer, but maybe things have changed or I got short-changed. Care to expound on this?

OK. What math??

I (hope) you had a plan before you went diving. Mulit-level or square makes no difference for this dive. You (should) know roughly where you are within your profile, being a sharp Padi diver, checking gauges often. Again, in your own words, you don't ride the NDL limit, so it should be evident that if you know you're well within the parameters that you dive under, that if the computer takes a dump, you won't be over any perceived limit, so a basic normal ascent is the procedure that is to be followed. (which I hope always includes 3-5min S/Stop regardless of profile).

Get on the boat, do your surface work/recalcs if you must etc, and carry on.

Part # 2:
Maybe Padi gave you an answer, and you just forgot.....Check the bottom of you RDP on side 2, or side 1 of the wheel version.

It doesn't say "computer poops out,this is what you do", but it does say emergency deco procedure, plus somewhere they also give you what to do if your puter stops working. To be honest, I wouldn't follow either answer, because they're just dumb, but I understand that they are being ultra conservative, and is effectively safer than what I would do. The problem being, it's so "conservative" (lost computer answer) that I actually think it's possibly rounded the curve into dangerous again!

Regards

Steve

 

[Scuba_Steve]

To further your chat with Jim,......

Then use the wheel. It ain't worth $70.00CDN, and I've been known to call it a POS, but it really is quite neat,..do not tell anyone I said that

Think logically about it, and toss a few minutes of conservatism into the mix. It'll be fine.

Hell to be honest, I can get a very rough calc for M/Level dives with the flat table for pete's sake!

Not to be complacent, but there's some slop to be used here. Add conservatism as you see fit and enjoy it. The dive shouldn't be about panicing if your profile is going to be OK. Think it out before hand, and monitor it in the water.

 

[O2BBubbleFree]

Steve, thanks for the comments.

I now realize that there are a few details that I posted on the other thread that I left out when I copied it here , plus a few are needed that I didn’t consider then. Let me fill in a few blanks.

This hypothetical dive is the typical boat dive where the only planning details I have are, “we’re going to drop down to about 80’ and cruise along the reef, rising along the way to about 60’. We’ll surface when you’re down to 500 psi”.

So I get out my trusty RDP and look up the NDL for 80’, and write it on my slate. Then I write the NDLs for 90’, 100’, 110’ on my slate, just in case. I also figure my own turn pressure based on the max depth given by the DM.

I start my stopwatch on descent, just in case.

During this dive, I dive the computer (for NDLs) and my gas gauge (for turn pressure). I know, plan the dive and dive the plan. If I am doing a square profile, that’s fine. When I’m not, I dive the computer.

Now, if the computer dies before I pass the RDPs NDL, I can use my stopwatch and the data on my slate to complete the dive per RDP.

If the computer dies after I’ve exceeded the RDP NDL, I abort the dive.

I didn’t consider the “emergency deco procedure,” as I wasn’t outside of the multi-level NDL. And, as you mentioned, it’s overkill for this scenario.

Now, to the question at hand. If I use the square-profile pressure group of the first dive to plan the second dive, how ‘conservative’ is that compared to the multi-level pressure group that the computer would have given me? I know, the farther I get from a square profile, the more overly-conservative this approach is going to be.

I was thinking that someone with simulation software might like to provide some data on different profiles, but now that I know that there is free software available, I plan to run a bunch of profiles to get a better feel for this.

Oh, and in case someone is wondering why I write the NDLs on a slate, instead of just carrying the RDP, I’ll give my logic on that one, too. Basically I don’t trust my brain, under the influence of nitrogen, to recalculate NDLs in the middle of the dive. If my computer implodes, I want the NDL info immediately available. On the first dive this isn’t a big deal, but it becomes more important with each repetitive dive. I consider it minimizing task loading.

So, what do you think?