Rec Vs. Technical???

[Octopusprime]

As I have continued to read the thread, I'm getting the feeling that you are exploring this for much the same reason that I got my tech cert. I wanted to go dive the cloud sponges in Saanich Inlet, which start at about 100 feet, but get dense enough for good photographs about 120. I didn't want to dive the Doria -- I just wanted a reasonable length of time at the depth where the things I wanted to see were to be found.

For me, that had to be trimix, in part because I'm simply too stupid to dive down there without it. But the UTD Tech 1 class, with 25/25 and O2 deco, was perfect for what I wanted to do. I took the class and then went up and did the dives just as I had envisioned doing them, and they were fabulous fun and we got some great photographs.

25/25 is not prohibitively expensive, and the gas supply for a reasonable dive (not 60 minutes!) at those depths is quite manageable.

Exactly... Not looking for super deep or super long... Does not need to be 60 min but longer than 10-13 min on air or maxing out nitrox at 28 min at 110ft. I have been reading about O2 deco sounds like it drastically shortens deco time. My main reason is to have some task time weather it is to get some photos, explore the wreck prectice some skills etc.

I prefer to dive wet just one less thing to worry about. I have been at 96ft at 42 deg for 20 min and was fine temprature wise. I will continue to practice dry to become more proficient.

 

[tbone1004]

you'll be thanking God for that drysuit on those deco hangs, and yes O2 drastically reduces deco times.

That profile that you originally asked for that I gave you had 32 minutes on O2, if you did it on backgas 28% on that dive, you'd have 85 minutes on those last two stops, go from 68 minutes total deco to 121 minutes of total deco, gets you out of the water almost an hour faster

 

[Aquavelvet]

Drysuits are fairly important for doing deeper and longer dives in cold water. It's not just a matter of being able to tolerate the cold. Staying warm is important for blood circulation and nitrogen off-gassing during the ascent.

I like being able to do modest deco dives of around 25 to 30 minutes bottom time at 110 to 120 ft. A single Alu 80 full of EAN50 greatly accelerates the decompression and can last for three dives of this nature. The TDI Advanced Nitrox / Deco Procedure class from a good instructor will get you on your way.


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[rivers]

Exactly... Not looking for super deep or super long... Does not need to be 60 min but longer than 10-13 min on air or maxing out nitrox at 28 min at 110ft. I have been reading about O2 deco sounds like it drastically shortens deco time. My main reason is to have some task time weather it is to get some photos, explore the wreck prectice some skills etc.

I prefer to dive wet just one less thing to worry about. I have been at 96ft at 42 deg for 20 min and was fine temprature wise. I will continue to practice dry to become more proficient.

But you also don't necessarily need to do O2 deco, or any sort of accelerated deco, in the 100 foot range. Using 32% at 100 feet, the deco is 1:1, as in, you do a 40 minute bottom time, you will have 10 minutes of deco at 6, with one minute at 50, 40, and 30 feet. Yes, you need a twinset for that dive, but you don't need any sort of deco stage.

 

[PfcAJ]

But you also don't necessarily need to do O2 deco, or any sort of accelerated deco, in the 100 foot range. Using 32% at 100 feet, the deco is 1:1, as in, you do a 40 minute bottom time, you will have 10 minutes of deco at 6, with one minute at 50, 40, and 30 feet. Yes, you need a twinset for that dive, but you don't need any sort of deco stage.

How is that a 1:1 deco?

40mins of bt to 13mins of deco in your example is not 1:1. Also, what algorithm and settings are you using to derive that deco time?

 

[rivers]

it's 1:1 at 6 is what I meant. I was on my phone at the time, so i didn't particularly expand on it. If you must know, it's what we discussed on Rec 3. and on multideco, I use a GF of 30/85 to work out my deco on anything not a 30m dive. But multideco gives this for a run on a 40 min, 30m dive:Surface interval = 5 day 0 hr 0 min.Elevation = 0m
Conservatism = GF 30/85


Dec to 30m (2) Nitrox 32 15m/min descent.
Level 30m 38:00 (40) Nitrox 32 1.27 ppO2, 24m ead
Asc to 12m (42) Nitrox 32 -9m/min ascent.
Stop at 12m 1:00 (43) Nitrox 32 0.70 ppO2, 9m ead
Stop at 9m 2:00 (45) Nitrox 32 0.61 ppO2, 6m ead
Stop at 6m 9:00 (54) Nitrox 32 0.51 ppO2, 4m ead
Surface (60) Nitrox 32 -1m/min ascent.


OTU's this dive: 60
CNS Total: 23.7%


3832.7 ltr Nitrox 32
3832.7 ltr TOTAL

So, not too far off.

 

[Jack Hammer]

it's 1:1 at 6 is what I meant....

?Huh?? Sorry, I'm not understanding what you are trying to convey here. How is it 1:1 @ 6m? 1:1 means there would be 40 minutes deco in your example. Id have a minute each at 15, 12, 9m, and 10 minutes @ 6m using back gas, less with a deco gas.

 

[rivers]

?Huh?? Sorry, I'm not understanding what you are trying to convey here. How is it 1:1 @ 6m? 1:1 means there would be 40 minutes deco in your example. Id have a minute each at 15, 12, 9m, and 10 minutes @ 6m using back gas, less with a deco gas.

For every minute over 30 minutes you're at 30m, you do a minute at 6 (for example 40 minutes at 30m=10 minutes at 6m), plus a minute at 15, 12, and 9.

I guess a better way to put it would be x minutes over min deco at 30m=x minutes at 6m

 

[TSandM]

BTW, a good resource for somebody to talk to in your area, who is NOT selling gear, is Duane Johnson, ppO2_diver here on SB. Duane's been around a very long time.

I also ran your 120 for 60 dive through V-planner, and it came out with almost the same amount of deco that Peter and I figured using RD, although V-planner moves it a little shallower. Using a .7 cfm SAC rate for bottom time and .5 for deco, I needed 200 cf of bottom gas and 31 cf of deco gas, which means you would need double 130's plus a bottom stage (to maintain rock bottom) and an 80 of 50% for deco (to maintain the 1.5 supply for lost deco gas). Not a fun dive for me, with big tanks and two 80's, but it would be doable.

By the RD I was taught, you do 1:1 at 150 -- gaining five minutes for each ten feet shallower, so you have 45 minutes at 120 for 30 min of deco; add the 15 for the overtime (60 - 45) and you get 45 minutes of deco. V-planner came up with 42, doing the dive on 25/25 with 50% for deco, so that was pretty darned close.

 

[Jack Hammer]

For every minute over 30 minutes you're at 30m, you do a minute at 6 (for example 40 minutes at 30m=10 minutes at 6m), plus a minute at 15, 12, and 9.

I guess a better way to put it would be x minutes over min deco at 30m=x minutes at 6m

I know it as the 130 rule. I figured that's what you meant.

The ratios are generally accepted to be the amount of deco time to the amount of bottom time. Hence, a 1:1 ratio on a dive with 40 minutes bottom time would call for 40 minutes deco. 10 minutes deco would be a much different ratio, 1:4.