Multideco... tips and tricks?

[inquis]

You're right, that plan isn't a good idea.

 

[rjack321]

I did a 2.5 hour dive yesterday, max depth only 54 meters, and took my o2 from 177 bar to 37 bar on an AL13. We've been discussing a 115 meter dive coming up in April and its got me concerned. I certainly can't use the 2L cylinder for that dive which, as it looks will be a 4 hour dive. Looking more like a full AL80 of 100% and a full AL80 of 10/60 would be enough but that recent 2.5 hour dive got me second guessing. I guess I need to re-figure out my o2 and dil consumption. This much o2 just for deco but then ?? (o2) and ?? (dil) for the working part of the dive...View attachment 874908

This dive becomes less and less worth it. The bailout costs would be absurd. View attachment 874909

Are you actually trained to MOD3? Why are you at setpoint 0.5 all the way down to 25m, then 1.4 to 115m then once you arrive switching to 1.1 on the bottom??

This plan is *nuts*, but not sure you have the training and experience to realize all the different reasons why.

Also, above and beyond the 115m plan, doing 54m 2.5hr dives on AL13s is.... unwise.

 

[Wibble]

I did a 2.5 hour dive yesterday, max depth only 54 meters, and took my o2 from 177 bar to 37 bar on an AL13. We've been discussing a 115 meter dive coming up in April and its got me concerned. I certainly can't use the 2L cylinder for that dive which, as it looks will be a 4 hour dive. Looking more like a full AL80 of 100% and a full AL80 of 10/60 would be enough but that recent 2.5 hour dive got me second guessing. I guess I need to re-figure out my o2 and dil consumption. This much o2 just for deco but then ?? (o2) and ?? (dil) for the working part of the dive...View attachment 874908

This dive becomes less and less worth it. The bailout costs would be absurd. View attachment 874909

Deep dives require at least 3 litre cylinders due to the runtime. 2 litre cylinders are for short dives.

177 - 33 = 144 x 2 = 288 litres oxygen used
2h30 = 150 mins
288 / 150 = 1.92 litres per minute average oxygen consumption.

Something is very wrong with that consumption rate. You’re very unlikely to be metabolising at that rate; you’re wasting the oxygen, probably during flushes or trying to run a high set point at the 6m stop. Most likely your ADV is frequently firing and diluting the loop and the controller constantly injects oxygen. Or you have a leak. Can you turn off your ADV using an ADV shutoff?

Your numbers indicate you have AI transmitters. This would have a log of gas consumption which you can see with Shearwater Cloud.

For comparison, I looked at one of my dives this year to 62m/210ft for 2h36 runtime. My oxygen usage was 150 litres and diluent was 120 litres (which is high as I’m a bit overweighted to allow bailing out and heavy SMB reel)

It is critical that you get the oxygen usage under control before you look at long MOD3 runtimes.


The plan you posted is very flawed. Looks like an Open Circuit plan, especially with the set points used. CCR would be very different with at least 20 mins on the bottom. The CCR part of the dive is simple; the difficulty is the bailout plan where you’d probably use 4 Ali80s with different gases for that depth: bottom gas, travel gas, intermediate deco gas, rich deco gas. For a 115m/380ft dive, you'd be looking at circa 4 hours or more for ~20 mins on the bottom. Obviously if diving a wreck, you'd not be on the bottom, so the dive would be shallower and you'd get longer. Have to plan for the max depth though.

For MOD3 dives you need to take into account many many other factors such as: gas densities; oxygen content; setpoints especially on the bottom; CNS & POT loadings; offboarding loop gas from bailout for failures; optimising bailout usage; scrubber durations; bailout gas costs and availability; thermal considerations (will your suit heater work for that long); myriad failures; etc. All of which are taught on MOD3 that has the absolute pre-requisite to have plenty of experience on MOD2 dives.

 

[justinthedeeps]

took my o2 from 177 bar to 37 bar on an AL13

Disregarding the rest of that post--which I can't begin to wrap my head around!

If you add a transmitter SPG to the oxygen (and dil) regs, you can start to compute pretty good statistics about your personal ranges of gas consumptions versus runtime and depths etc.

You can take values from the dive logs on Shearwater Cloud and precisely calculate your diluent and O2 consumptions from time and pressure data [as well as basal consumption rates for the bottom phase], and begin to understand and project quartile ranges of how much dil and O2 you would consume on future dives (plus reserve)

I started doing this for some recent dives in spreadsheets as part of my DIY dive logs, it is not too difficult to do.

 

[LFMarm]

The biggest tip is, enter all the gases you can imagine. Enter all the dive plans you can imagine. Then use the check box to enable them, click the red X (which won't yet delete them) and click Edit (instead of Delete) to match up with your actual plans.

That's MD's biggest advantage over Subsurface. In Subsurface you can only delete a gas or a segment when you want to compare variations. Then, you have to go back and reenter them if you want to return to your original plan. Unless there's a Subsurface trick I'm unaware of...

You can do the same in subsurface: program all gasses and activate only the ones you want to build into your plan. As far as I know, you cannot preprogram dives (depth, duration) but this is pretty quick to change.

 

[addohm]

Are you actually trained to MOD3? Why are you at setpoint 0.5 all the way down to 25m, then 1.4 to 115m then once you arrive switching to 1.1 on the bottom??

This plan is *nuts*, but not sure you have the training and experience to realize all the different reasons why.

Also, above and beyond the 115m plan, doing 54m 2.5hr dives on AL13s is.... unwise.

No. My mod3 class is scheduled for next April. But that's not going to stop me from thinking about dive plans, learning, etc. Also, my 2.5 hour dive was with enough bailout gas to end the dive at the deepest and furthest point of the dive. I'm not here to discuss that really. I'm trying to learn how to use multideco properly on CCR; so thank you for pointing out the setpoint issue. It is supposed to be switched to 1.1 at 20 meters on descent but I'm sure I left some things messy while screwing around with settings in multideco.

 

[addohm]

Disregarding the rest of that post--which I can't begin to wrap my head around!

If you add a transmitter SPG to the oxygen (and dil) regs, you can start to compute pretty good statistics about your personal ranges of gas consumptions versus runtime and depths etc.

You can take values from the dive logs on Shearwater Cloud and precisely calculate your diluent and O2 consumptions from time and pressure data [as well as basal consumption rates for the bottom phase], and begin to understand and project quartile ranges of how much dil and O2 you would consume on future dives (plus reserve)

I started doing this for some recent dives in spreadsheets as part of my DIY dive logs, it is not too difficult to do.
View attachment 874926View attachment 874927

I've got transmitters on all the gasses I use for every dive I do except for offboard deco bottles. The RMV average is wildly different for every dive so I don't really give it a lot of credence. I need to do a proper RMV measurement again. Haven't done it since last year.

 

[addohm]

Deep dives require at least 3 litre cylinders due to the runtime. 2 litre cylinders are for short dives.

177 - 33 = 144 x 2 = 288 litres oxygen used
2h30 = 150 mins
288 / 150 = 1.92 litres per minute average oxygen consumption.

Something is very wrong with that consumption rate. You’re very unlikely to be metabolising at that rate; you’re wasting the oxygen, probably during flushes or trying to run a high set point at the 6m stop. Most likely your ADV is frequently firing and diluting the loop and the controller constantly injects oxygen. Or you have a leak. Can you turn off your ADV using an ADV shutoff?

Your numbers indicate you have AI transmitters. This would have a log of gas consumption which you can see with Shearwater Cloud.

For comparison, I looked at one of my dives this year to 62m/210ft for 2h36 runtime. My oxygen usage was 150 litres and diluent was 120 litres (which is high as I’m a bit overweighted to allow bailing out and heavy SMB reel)

It is critical that you get the oxygen usage under control before you look at long MOD3 runtimes.


The plan you posted is very flawed. Looks like an Open Circuit plan, especially with the set points used. CCR would be very different with at least 20 mins on the bottom. The CCR part of the dive is simple; the difficulty is the bailout plan where you’d probably use 4 Ali80s with different gases for that depth: bottom gas, travel gas, intermediate deco gas, rich deco gas. For a 115m/380ft dive, you'd be looking at circa 4 hours or more for ~20 mins on the bottom. Obviously if diving a wreck, you'd not be on the bottom, so the dive would be shallower and you'd get longer. Have to plan for the max depth though.

For MOD3 dives you need to take into account many many other factors such as: gas densities; oxygen content; setpoints especially on the bottom; CNS & POT loadings; offboarding loop gas from bailout for failures; optimising bailout usage; scrubber durations; bailout gas costs and availability; thermal considerations (will your suit heater work for that long); myriad failures; etc. All of which are taught on MOD3 that has the absolute pre-requisite to have plenty of experience on MOD2 dives.

On this particular dive I made some configuration changes that probably had some affect on my consumption, mainly I switched from ADV\MAV to MAV only to have better control over minimum loop volume (admittedly I did like the ADV better, especially for having busy hands, but I must give it several more dives before deciding). On top of that I was leading which we all know can have quite the effect on your consumption and air management. Also, I am still having a very difficult time managing my CCR trim and buoyancy at shallow depths. All excuses and also facts. I use Garmin for my air integration. For reference a previous dive at the same location with relatively consistent displayed RMV values, 1h50m average depth 21m I went from 179 BAR to 89 and a supposed average RMV of 8.7L. Another dive, same location, 1h54m average depth 21m I went from 184 to 89 and a supposed average RMV of 6.4L.

 

[rjack321]

Also, I am still having a very difficult time managing my CCR trim and buoyancy at shallow depths.

You should work this out now, before anymore deco dives at all. You need to be stable to do multi hour hangs. Yes they are boring - but all your wiggling and bouncing around is both metabolizing and venting off O2 and to a lesser extent dil.

I would seriously reconsider if you're ready for MOD3 4.5 months from now.

 

[addohm]

You should work this out now, before anymore deco dives at all. You need to be stable to do multi hour hangs. Yes they are boring - but all your wiggling and bouncing around is both metabolizing and venting off O2 and to a lesser extent dil.

I would seriously reconsider if you're ready for MOD3 4.5 months from now.

I appreciate your concerns and input. To name off some relevant certifications, I'm certified cave, tec deep, hypoxic trimix, extended range, deco procedures, advanced nitrox, and have been diving almost 25 years. CCR is new to me and has humbled me this past year with regards to trim and buoyancy, but that doesn't render my past knowledge and experience useless. Again, I am just trying to learn multideco for future hopes and dreams. We've derailed this discussion unfortunately.