OP
ps. I also get that 60 or 70% gets me out the fastest, as compared to 50, 80, or 100.
Planning multi-level deco dive?
- Thread starter stuartv
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OP
Since the thread has gone this way, I'm going to really put myself out there. This is a tentative plan.
Back gas consumption is 200 cu-ft, if I do the deco on back gas. I'll be using double 120s, so very comfortable.
Note that the Subsurface planner lets you plan legs that are a constant ascent. So, the leg that says 85ft for 20 minutes is actually a 20 minute ascent from 145' (the previous leg) to 85. And, for that matter, the leg for 145' for 2 minutes is actually a 2 minute ascent from 160 to 145.
This is just a very tentative plan, pending getting more info from the dive operator. It's just based on reading about the O and understanding that the flight deck is at 145. So, my thinking is to descend just past that and, hopefully, get a peek into the hangar deck (possible lightzone penetration - just to get inside an opening and look around for a couple of minutes). Then back up to the flight deck and swim to the tower. Then make a nice slow ascent, exploring the tower on the way up.
I feel like this plan is pretty conservative. It allows for the possibility of deco on back gas. But, if things go like they should, it's a reasonable and safe dive. Long enough to be worth it, but not pushing my limits. And the riskiest part of the dive (the hangar deck) is at the very beginning, leaving me plenty of time to deal with it if there's a problem.
And, based on the earlier parts of this thread, plenty of opportunity to monitor my TTS and computer ascent plan and extend my time exploring the tower on the way up.
And it leaves me enough deco gas to share with my buddy.
Constructive criticism is welcome.
Back gas consumption is 200 cu-ft, if I do the deco on back gas. I'll be using double 120s, so very comfortable.
Note that the Subsurface planner lets you plan legs that are a constant ascent. So, the leg that says 85ft for 20 minutes is actually a 20 minute ascent from 145' (the previous leg) to 85. And, for that matter, the leg for 145' for 2 minutes is actually a 2 minute ascent from 160 to 145.
This is just a very tentative plan, pending getting more info from the dive operator. It's just based on reading about the O and understanding that the flight deck is at 145. So, my thinking is to descend just past that and, hopefully, get a peek into the hangar deck (possible lightzone penetration - just to get inside an opening and look around for a couple of minutes). Then back up to the flight deck and swim to the tower. Then make a nice slow ascent, exploring the tower on the way up.
I feel like this plan is pretty conservative. It allows for the possibility of deco on back gas. But, if things go like they should, it's a reasonable and safe dive. Long enough to be worth it, but not pushing my limits. And the riskiest part of the dive (the hangar deck) is at the very beginning, leaving me plenty of time to deal with it if there's a problem.
And, based on the earlier parts of this thread, plenty of opportunity to monitor my TTS and computer ascent plan and extend my time exploring the tower on the way up.
And it leaves me enough deco gas to share with my buddy.
Constructive criticism is welcome.
Code:
Subsurface dive plan
based on Bühlmann ZHL-16B with GFlow = 50 and GFhigh = 85
depth duration runtime gas
160ft 3min 3min (23/20)
160ft 7min 10min
145ft 2min 12min
85ft 20min 32min
40ft 2min 34min
40ft 1min 35min EAN70
30ft 2min 37min
20ft 12min 49min
0ft 1min 50min
CNS: 23%
OTU: 59
Gas consumption:
156cuft/2250psi of (23/20) (3cuft/42psi in planned ascent)
16cuft/1216psi of EAN70 (16cuft/1216psi in planned ascent)
Stuart is planning to use a single deco gas for this dive, but re: the previous conversations here on the topic, multiple deco gases aren't going to make a big difference for this dive. On the kind of profile stuart is talking about, using: EAN 32 & 80 or 40 & 80 or 40 & 90 or 50 & 100, all come in within about 3 minutes of each other. I don't know Stuart's SAC, but this kind of dive using double 120s for back gas and a 40 of deco of (choose your mix) will be a pretty conservative dive.
Also, it takes a couple of more minutes, but you can manually put in quite a few intermediate depths into Multi-Deco and run various profiles.
Also, it takes a couple of more minutes, but you can manually put in quite a few intermediate depths into Multi-Deco and run various profiles.
waterpirate
Contributor
FWIW,
I think that your choice of back gas is incorrect for this " bounce to 160 " to take a look. You have the time between now and turkey day to get in the pool, or get in a quarry and handle more than 1 bottle. This dive plan screams for a stage for your deep quick look, and back gas that is useable for the tower starting at 130' up to 85'. A al 80 filled with 21/20 would get you in for a look deep, switch to back gas 32/20 at the depth that you feel safe, and deco on whatever you choose. Doing deco on deep mix sucks, so why plan on it? A switch to a higher mix will do wonders for your bottom time while limiting your exposure to total deco as off gassing will start when you make your first gas switch on your ascent. The other thing to note about dive planning for deco is your run time. You need to tell the mate what your RT is and do not deviate. How else will they know if you are overdue?
I am a stroke and this advice may kill you or do you harm.
My other set of hp 100's are back with a fresh hydro and vip. Valves were sonic cleaned and rebuilt. Send me a PM if you have any interest in them. I will make you a sweetheart deal on all the tanks I have left and everything else in the scuba shed. Say $550.00
Eric
I think that your choice of back gas is incorrect for this " bounce to 160 " to take a look. You have the time between now and turkey day to get in the pool, or get in a quarry and handle more than 1 bottle. This dive plan screams for a stage for your deep quick look, and back gas that is useable for the tower starting at 130' up to 85'. A al 80 filled with 21/20 would get you in for a look deep, switch to back gas 32/20 at the depth that you feel safe, and deco on whatever you choose. Doing deco on deep mix sucks, so why plan on it? A switch to a higher mix will do wonders for your bottom time while limiting your exposure to total deco as off gassing will start when you make your first gas switch on your ascent. The other thing to note about dive planning for deco is your run time. You need to tell the mate what your RT is and do not deviate. How else will they know if you are overdue?
I am a stroke and this advice may kill you or do you harm.
My other set of hp 100's are back with a fresh hydro and vip. Valves were sonic cleaned and rebuilt. Send me a PM if you have any interest in them. I will make you a sweetheart deal on all the tanks I have left and everything else in the scuba shed. Say $550.00
Eric
Michael Guerrero
Contributor
For my Oriskany dives I usually plan 150' or 160' for 45 or 50 min wearing double HP130s, slinging an AL80 of 50% and AL40 of 100%. I get out of the water right around the 2hr mark, usually with about 1/3 of my backgas and about half my deco gas. The ship is big enough that you could spend the entire time at depth. I've spent multiple dives with almost all my planned time at depth (with some dips down deeper /wink).
Here's a video of my last one if you want to scout out some locations at the stern.
If you do less than your planned bottom time at depth, you should be fine. Just keep an eye on your computer(s). As for losing deco gas and diving with a buddy, if you want to sling only one bottle then you could add a second 2nd stage to it so you guys aren't trying to buddy breathe for a bunch of deco. In that case I'd both carry AL80s with 100%.
However, using a second deco gas would shorten your time and would be my recommendation.
Also, it might be a bad assumption to expect to find a insta-buddy for a technical dive on the O in November. First of all, Floridians are notoriously wussy when it comes to "cold" water (i.e., anything below the mid-80s). Second, most divers who go out to the O are not tech certified in my experience, and if they are they likely already have a buddy. Third, there is no certainty that you can hire a divemaster to take you down. For the boats I've been on out of Pensacola, the DM is focused on the shallow divers and does not have doubles or deco bottles. The only other tech divers I've encountered were using rebreathers, so not a good fit.
Something to consider. All my dives on the O have been intentionally solo, but had I wanted an insta-buddy, none would have been available for any of them.
Enjoy the dive and beware the barracuda.
Here's a video of my last one if you want to scout out some locations at the stern.
If you do less than your planned bottom time at depth, you should be fine. Just keep an eye on your computer(s). As for losing deco gas and diving with a buddy, if you want to sling only one bottle then you could add a second 2nd stage to it so you guys aren't trying to buddy breathe for a bunch of deco. In that case I'd both carry AL80s with 100%.
However, using a second deco gas would shorten your time and would be my recommendation.
Also, it might be a bad assumption to expect to find a insta-buddy for a technical dive on the O in November. First of all, Floridians are notoriously wussy when it comes to "cold" water (i.e., anything below the mid-80s). Second, most divers who go out to the O are not tech certified in my experience, and if they are they likely already have a buddy. Third, there is no certainty that you can hire a divemaster to take you down. For the boats I've been on out of Pensacola, the DM is focused on the shallow divers and does not have doubles or deco bottles. The only other tech divers I've encountered were using rebreathers, so not a good fit.
Something to consider. All my dives on the O have been intentionally solo, but had I wanted an insta-buddy, none would have been available for any of them.
Enjoy the dive and beware the barracuda.
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packrat12
Contributor
Stuartv - The plan looks pretty good to me. I have seen AN/DP divers on the Hydro Atlantic in Pompano struggling with 2 tanks when they did not need to be. Bluntly, we had given up on him making proper switches and maintaining stops. I am strongly believe that, because you are doing a short bounce to 165', the idea of staging a tank for the bounce is just over complicating things. I have done a dive for 172' for 26 minutes, cleared deco at 57 minutes and a total RT of 67 minutes. Mix: ~260 CF of 21/0 and Deco 40 CF of 76/0. I spent most of my time at about 140 - 145'. I had more than ample gas in both at the end. Your dive will not be that deep for the duration and your gas planning looks similar to what I had. You will also have superstructure and lines to assist surfacing so I would not call it a stressful dive. I agree with finding buddies and insta-buddies in this case. The gulf is just too cold for us Floridians.
I would highly resist complicating the dive with lots of extra gear. My only comment on the plan is why GF 50/85? More often it is GF 30/85 which will have a little less bubble stress.
I would highly resist complicating the dive with lots of extra gear. My only comment on the plan is why GF 50/85? More often it is GF 30/85 which will have a little less bubble stress.
So you want to do a 30 minute dive to 160ft (48m)?
Since you mentioned 21/20, I assume you're Trimix certified?
Why not take a set of 21/35 doubles and an al80 of 50%
Wait, you want to go deeper than 150ft, so make that 18/45 ...
30 min at 160ft ~ 35min of deco with your first stop at 80ft for a minute most likely.
If you average depth it up (down?) -multilevel profile- to 130ft, that deco shrinks to ~ 20 minutes of deco for 30 minutes... Or stay longer to 45 minutes of bottom time for 35 minutes of deco.
An AL80 of 50% holds about 35 minutes of gas for deco (including 1/3 for team resources)
Double 100's will hold enough gas for 30 minutes at 160ft and meet RB/MG
_R
Since you mentioned 21/20, I assume you're Trimix certified?
Why not take a set of 21/35 doubles and an al80 of 50%
Wait, you want to go deeper than 150ft, so make that 18/45 ...
30 min at 160ft ~ 35min of deco with your first stop at 80ft for a minute most likely.
If you average depth it up (down?) -multilevel profile- to 130ft, that deco shrinks to ~ 20 minutes of deco for 30 minutes... Or stay longer to 45 minutes of bottom time for 35 minutes of deco.
An AL80 of 50% holds about 35 minutes of gas for deco (including 1/3 for team resources)
Double 100's will hold enough gas for 30 minutes at 160ft and meet RB/MG
_R
Rainer
Contributor
Not at all ...
Metric here (without rounding) ...
11L @ 207 bar = 2277L
Avg ATA from 21m to 6m is 2.05 ATA (21-9m & 6m)
20L/min SAC
1/3 of 2277L is 1518L remaining
1518 / 20 / 2.05= 37 minutes
But most people should have a SAC better than 20L at this level .... factors in some stress/environment
_R
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Rainer
Contributor
That's crazy high for deco (like twice my usual deco SCR). Thankfully I haven't had to do such dives with anyone going through gas like that. What do you plan for the bottom portion of the dive where you're theoretically working harder (kicking around, taking photos/video, navigating, etc)?
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