Question Question for Experienced O2ptima CM Divers

[DiveTucson]

Glad you thought so. I fire students like this. Ask for help, then don’t listen to any of the advice of the experts. They call that an “askhole”

Your dive planning is absolute garbage. Throw it all away and start again.

This!

 

[rx7diver]

I thought I would look at this question (i.e., how does one solo dive safely a CM + isolator-manifolded double LP50's) from a different perspective.

It seems clear (to me) that, providing I can carry enough deco gas in each of two deco cylinders (here, two Al 40's) for these types of dives (here, TOD = 165 fsw), the max BT is constrained/determined by the amount of gas required to return from the farthest point out, back to the 70 fsw depth, breathing open circuit from only one of the LP50's, retracing my descent route.

It seems clear (to me) that, since a LP50 (48.7 cu ft at 2,600 psig) has capacity of ~55 cu ft at 3,000 [sic] psig, the return trip back to 70 fsw on open circuit "must" not require more than ~55 cu ft.

Using Tri-Mix with FO2 = 0.23, FHe = 0.28, and FN2 = 0.49 (mixed from 28% He and 72% EAN32), and my earlier assumptions (i.e., 60 fpm descent rate, 30 fpm ascent rate, working RMV = 0.60 ft^3/min), my old deco software yielded the following:

1. For a 30 min BT on open circuit, the return to 70 fsw from the turnaround point, requires ~62 ft^3 of Tri-Mix.

2. For a 25 min BT, the return requires ~53 ft^3.

3. For a 20 min BT, the return requires ~45 ft^3.

Upshot: Looks like the longest safe solo dive I can plan for this 165 fsw dive, using a CM + isolator-manifolded double LP50's with Tri-Mix 23/28 and an oxygen set-point of 1.4 ATA, is 25 minutes bottom time.

So, longer dives at this TOD necessarily (for me) requires larger back-mounted doubles!

Note: When I first began extended range Great Lakes shipwreck diving (open circuit, buddy diving, air as a bottom gas, accelerated deco using oxygen) in the mid-1990's, I wore isolator-manifolded HP100's, and this dive plan (165 ffw for a 25 min BT) was a very typical plan.

Comments?

rx7diver

 

[DiveTucson]

I thought I would look at this question (i.e., how does one solo dive safely a CM + isolator-manifolded double LP50's) from a different perspective.

It seems clear (to me) that, providing I can carry enough deco gas in each of two deco cylinders (here, two Al 40's) for these types of dives (here, TOD = 165 fsw), the max BT is constrained/determined by the amount of gas required to return from the farthest point out, back to the 70 fsw depth, breathing open circuit from only one of the LP50's, retracing my descent route.

It seems clear (to me) that, since a LP50 (48.7 cu ft at 2,600 psig) has capacity of ~55 cu ft at 3,000 [sic] psig, the return trip back to 70 fsw on open circuit "must" not require more than ~55 cu ft.

Using Tri-Mix with FO2 = 0.23, FHe = 0.28, and FN2 = 0.49 (mixed from 28% He and 72% EAN32), and my earlier assumptions (i.e., 60 fpm descent rate, 30 fpm ascent rate, working RMV = 0.60 ft^3/min), my old deco software yielded the following:

1. For a 30 min BT on open circuit, the return to 70 fsw from the turnaround point, requires ~62 ft^3 of Tri-Mix.

2. For a 25 min BT, the return requires ~53 ft^3.

3. For a 20 min BT, the return requires ~45 ft^3.

Upshot: Looks like the longest safe solo dive I can plan for this 165 fsw dive, using a CM + isolator-manifolded double LP50's with Tri-Mix 23/28 and an oxygen set-point of 1.4 ATA, is 25 minutes bottom time.

So, longer dives at this TOD necessarily (for me) requires larger back-mounted doubles!

Note: When I first began extended range Great Lakes shipwreck diving (open circuit, buddy diving, air as a bottom gas, accelerated deco using oxygen) in the mid-1990's, I wore isolation-manifolded HP100's, and this dive plan (165 ffw for a 25 min BT) was a very typical plan.

Comments?

rx7diver

Here is my last comment on this dumpster fire. You are ignoring the comments about CCR gas planning from THREE Chest Mount O2ptima Instructors. Based on this post there is nothing left to say, you already think you know everything and you have no clue about how to plan for a CCR dive solo or not. I hope you find the correct training before executing these dives because it is clear to me that you are unwilling to listen, learn, or take any advice.

 

[Superlyte27]

If this guy weren’t so friggin oblivious and annoying I’d GIVE him a CM class and AN&DP class just to fix his errors in planning.

I can’t stand askholes.

 

[broncobowsher]

Here is my last comment on this dumpster fire. You are ignoring the comments about CCR gas planning from THREE Chest Mount O2ptima Instructors. Based on this post there is nothing left to say, you already think you know everything and you have no clue about how to plan for a CCR dive solo or not. I hope you find the correct training before executing these dives because it is clear to me that you are unwilling to listen, learn, or take any advice.

Thanks Ben. It's like a dumpster fire full of magnesium, add water and it just gets worse.

 

[azstinger11]

Thanks Ben. It's like a dumpster fire full of magnesium, add water and it just gets worse.

Oh I like that one! I’m stealing it lol

 

[lostsheep]

How

I thought I would look at this question (i.e., how does one solo dive safely a CM + isolator-manifolded double LP50's) from a different perspective.

It seems clear (to me) that, providing I can carry enough deco gas in each of two deco cylinders (here, two Al 40's) for these types of dives (here, TOD = 165 fsw), the max BT is constrained/determined by the amount of gas required to return from the farthest point out, back to the 70 fsw depth, breathing open circuit from only one of the LP50's, retracing my descent route.

It seems clear (to me) that, since a LP50 (48.7 cu ft at 2,600 psig) has capacity of ~55 cu ft at 3,000 [sic] psig, the return trip back to 70 fsw on open circuit "must" not require more than ~55 cu ft.

Using Tri-Mix with FO2 = 0.23, FHe = 0.28, and FN2 = 0.49 (mixed from 28% He and 72% EAN32), and my earlier assumptions (i.e., 60 fpm descent rate, 30 fpm ascent rate, working RMV = 0.60 ft^3/min), my old deco software yielded the following:

1. For a 30 min BT on open circuit, the return to 70 fsw from the turnaround point, requires ~62 ft^3 of Tri-Mix.

2. For a 25 min BT, the return requires ~53 ft^3.

3. For a 20 min BT, the return requires ~45 ft^3.

Upshot: Looks like the longest safe solo dive I can plan for this 165 fsw dive, using a CM + isolator-manifolded double LP50's with Tri-Mix 23/28 and an oxygen set-point of 1.4 ATA, is 25 minutes bottom time.

So, longer dives at this TOD necessarily (for me) requires larger back-mounted doubles!

Note: When I first began extended range Great Lakes shipwreck diving (open circuit, buddy diving, air as a bottom gas, accelerated deco using oxygen) in the mid-1990's, I wore isolator-manifolded HP100's, and this dive plan (165 ffw for a 25 min BT) was a very typical plan.

Comments?

rx7diver

How are you coming up with 62 ft^3 to ascend from 165’ to 70’ at 30 minutes BT?

You should be able to ascend directly to 70’. Let’s call that 3.5 minutes doubling your breathing to 1.2 ft^3 / min ; I come up with ~20 ft^3. Add some bottom time to that for exiting a wreck and/or problem solving and you're still below your estimate.

I’m all for excess bailout but you seem to be omitting info from us, missing pertinent knowledge yourself, or you are just bad at arithmetic.

I am not an instructor and I’m estimating in my head while stuck in traffic; I reserve the right to have made my own mistakes but it seems ballpark based on previous dives in this range. FWIW, literally just did ~160’ for 30 min BT, that’s what I’m driving home from.

 

[jlcnuke]

Looks like longest safe solo dive I can plan for this 165 fsw dive, using a CM + isolator-manifolded double LP50's with Tri-Mix 23/28 and an oxygen set-point of 1.4 ATA, is 25 minutes bottom time.

My comment would be that this is incorrect. The longest dive you can plan for this dive is 0 minutes, as you clearly don't yet have the training to plan a trimix dive, a CCR dive, or a mixed-gas CCR dive.

If you want to figure out how to do this kind of diving, get the training to learn how to do this type of diving.

 

[Superlyte27]

At

My comment would be that this is incorrect. The longest dive you can plan for this dive is 0 minutes, as you clearly don't yet have the training to plan a trimix dive, a CCR dive, or a mixed-gas CCR dive.

If you want to figure out how to do this kind of diving, get the training to learn how to do this type of diving.

At first I thought he was a troll. Then I looked at his profile and saw that he was a PhD. Which really (and I think literally in this case) stands for Piled Higher and Deeper.

 

[rx7diver]

How


How are you coming up with 62 ft^3 to ascend from 165’ to 70’ at 30 minutes BT?

You should be able to ascend directly to 70’. Let’s call that 3.5 minutes doubling your breathing to 1.2 ft^3 / min ; I come up with ~20 ft^3. Add some bottom time to that for exiting a wreck and/or problem solving and your still below your estimate.

I’m all for excess bailout but you seem to be omitting info from us, missing pertinent knowledge yourself, or you are just bad at arithmetic.

I am not an instructor and I’m estimating in my head while stuck in traffic; I reserve the right to have made my own mistakes but it seems ballpark based on previous dives in this range. FWIW, literally just did ~160’ for 30 min BT, that’s what I’m driving home from.

53.2 [sic] ft^3 is from the software output: The turnaround happens at RT = 12.5 min. So, 44.6 ft^3 to return to begin the ascent, and 8.6 ft^3 to ascend from 165 [sic] fsw to 70 fsw at 30 fpm.

I'll check these figures by hand in a short while, after I finish watching the evening news.

For this exercise, I require that you must retrace your route when you return--just in case you might be required to IRL (for example due to current, overhead boat traffic, etc.).

ETA (Corrected, after double-checking): Just checked during commercial break. My hand calculations yield: 53.7 43.8 ft^3 = 44.6 35.1 ft^3 required to return (12.5 9.75 min) to begin the ascent, and 8.7 ft^3 to ascend (3.2 min) from 165 fsw to 70 fsw at 30 fpm. I'll double-check later. Corrected, because only need to travel back 9.75 min (rather than 12.5 min) to get to spot to begin ascent.

rx7diver