Sidemount and nitrox mix

[Jai Bar]

לל

You read my mind

---------- Post added June 4th, 2013 at 04:24 PM ----------



Who requires an AN card for 28%? I'll be sure to avoid them...

---------- Post added June 4th, 2013 at 04:31 PM ----------




Don't do this. It's not the proper way to do things. Lets say you're at 130' and suffer a complete gas loss of your 26%. What do you have left? 38%? Good luck with that. So now you're really at 130' with only one tank, no real/proper redundancy. Sure, you can shoot up to 80' while you're switching to your backup gas, but do we really want to start planning your dives this way?

I know it's not convenient. Life sucks. But take two tanks of the gas that will support you at all stages of the dive. That's really the reason for sidemount anyway right? So, 26% at 130' is good all the way from 1' -130'. But, 38% isn't.

This is the reason why so many of us have so many stupid tanks. It sucks, but there's a right way, and a way that doesn't allow for the ****e to hit the fan. Always plan for the fan splatter, and you'll live.

---------- Post added June 4th, 2013 at 04:33 PM ----------



What agency do you teach for? The reason I ask is that what you just posted is opposite of what every agency out there teaches. OP, don't listen to this. It's possible it could get you in trouble.

---------- Post added June 4th, 2013 at 04:37 PM ----------



Yah, that disclaimer makes it all better. NOT!
Guys, making a full day of dives at 1.6 very possibly could kill you. We have no idea what your health is, what meds you are on, what water temps, work loads, currents, etc. are for you in a given day. Neither did NOAA. That's why it's recommended not to exceed 1.4.

Dear God, if this isn't the perfect thread for why you shouldn't learn to dive from Scubaboard, I don't know what is.

WOW!!!

Yeah, lucky me I'm not teaching nobody on the internet or anywhere else, retired. Myself, nowadays I only dive and muck in the water for fun and for fun only, just to watch the fish, take some photos and the such.

Used to dive for years upon years on ppo2 2.0, then another decade or so with 1.8- and the worst part of it was that nobody asked me whether I wanted it or liked it... But for the last decade I have free choice to dive every day between 1.6 to whatever ean36 yields at shallower depths.

But hey, maybe that's the reason I'm not going to live as long as the ones following NOAA's thoughtful recommendations of < 1.4. I strongly advice not to follow my reckless way of diving, probably better follow recommendations of NOAA, PADI, GUE or whatever organization you choose, and sure- the internet is not a place to learn scuba! At best, it's a place to share thoughts and ideas about life, the universe and everything

Sent from my myTouch 4G

 

[Superlyte27]

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Yeah, lucky me I'm not teaching nobody on the internet or anywhere else, retired. Myself, nowadays I only dive and muck in the water for fun and for fun only, just to watch the fish, take some photos and the such.

Used to dive for years upon years on ppo2 2.0, then another decade or so with 1.8- and the worst part of it was that nobody asked me whether I wanted it or liked it... But for the last decade I have free choice to dive every day between 1.6 to whatever ean36 yields at shallower depths.

But hey, maybe that's the reason I'm not going to live as long as the ones following NOAA's thoughtful recommendations of < 1.4. I strongly advice not to follow my reckless way of diving, probably better follow recommendations of NOAA, PADI, GUE or whatever organization you choose, and sure- the internet is not a place to learn scuba! At best, it's a place to share thoughts and ideas about life, the universe and everything

Sent from my myTouch 4G

Hey Rocket Scientist... Do you know why the Navy and NOAA don't recommend diving at 2.0 anymore? Uh, because people kept dying. DUH!
Yeah, I used to type on a type writer. I used to talk on a phone that was connected via a wire to the wall. I used to drive a car with biased ply tires. Sure, I've lost bread in a toaster and pulled it out with a butter knife. Guess what? We learned and evolved and developed better/safer ways of doing things.

If you're not instructing, do us a favor, and don't advise a newer diver to dive something that is opposite every single organization's (both recreation, technical, commercial and military) standpoint.

 

[a878bob]

I think I must be missing something as well. 130' on 28% might get you how much bottom time w/o deco? 5-6 minutes. So somebody who wants to do a deco dive is asking about how to do theses dives on 2 main cylinders only ? Just by quick figuring, maybe 20min at 130', with 50% deco. 2hr SI, 80' for maybe 30 min with 50%, what do you think, with 2 Hp 100's, and 1 40 with 50%, and hope you have some good dives in the big lakes prior to taking this on. It ain't blue water with pretty fish, I have known some pretty experienced guys who have a hard time doing just the 60 to 80 ' dives.

 

[rhwestfall]

I think I must be missing something as well. 130' on 28% might get you how much bottom time w/o deco? 5-6 minutes. So somebody who wants to do a deco dive is asking about how to do theses dives on 2 main cylinders only ? Just by quick figuring, maybe 20min at 130', with 50% deco. 2hr SI, 80' for maybe 30 min with 50%, what do you think, with 2 Hp 100's, and 1 40 with 50%, and hope you have some good dives in the big lakes prior to taking this on. It ain't blue water with pretty fish, I have known some pretty experienced guys who have a hard time doing just the 60 to 80 ' dives.

No, the OP needs to understand the gasses better, but, this past Saturday, we did just that here on Lake Erie....(true square profiles)

Dive#1 - 120 to the mud - 118' max, 26 minutes total dive time (left bottom with 3-4 min left in NDL), 1 min deep stop, and 3+ min safety at 15'
offhand, I don't recall the SI, but 1-1.5 hour seem about right IIRC
Dive #2 - 110 to the mud - 99' max, 28 minutes total dive time (left botton with 3-4 min left in NDL), 1 min deep stop, and 3+ min safety at 15'

single HP120 (air in this case, but we usually are using 28% for the 120-130 depths), and a slung 30 for a "safety blanket"... just normal recreational diving here (note: these are not penetration dives)...

 

[JamesK]

This thread scares the brown stinky stuff out of me.

OP, do not take two different gases. Use 1 gas that works for your deepest dive on both tanks. Taking a gas 50' below its MOD is stupid and downright dangerous. Don't anyone give me crap about deep tech dives with travel, bottom, and deco gasses. This is not the same.

If you just have to have a rich mix for your second dive, although I can't understand why, take separate tanks.

 

[chrpai]

Third - One assumes a diver would carry two different nitrox mixes to make optimal use of the nitrox at two different depths on the same dive. Thus the diver would be taking one of those mixes below its MOD.

Maybe, maybe not. Perhaps the scenario is as simple as a diver has one tank with 21% and one with 32% in it and he just wants to get the most NDL. A switch on my DG03 is as easy as pushing a button but doing it over and over does seem to be inviting trouble.

I'm not side mount, I'm a single 95 and a 40 stage. I can envision scenarios where I'd do a switch but none of them seem worthwhile to bother...

KISS

 

[Superlyte27]

No, the OP needs to understand the gasses better, but, this past Saturday, we did just that here on Lake Erie....(true square profiles)

Dive#1 - 120 to the mud - 118' max, 26 minutes total dive time (left bottom with 3-4 min left in NDL), 1 min deep stop, and 3+ min safety at 15'
offhand, I don't recall the SI, but 1-1.5 hour seem about right IIRC
Dive #2 - 110 to the mud - 99' max, 28 minutes total dive time (left botton with 3-4 min left in NDL), 1 min deep stop, and 3+ min safety at 15'

single HP120 (air in this case, but we usually are using 28% for the 120-130 depths), and a slung 30 for a "safety blanket"... just normal recreational diving here (note: these are not penetration dives)...

These are not square profiles. You said you did 118' for an RT of :26 minutes and left with 3-4 minutes of NDL? On Air? Not possible with a square profile. A square profile would mean you descended to 118' and stayed at 118' for 10'ish minutes (you said you still had 3-4 minutes of NDL) My tables show 120' good for :12 minutes.

So lets say you did 118' and it took you 2.5 minutes to reach depth...(using 45fpm to descend) you stay for 10 minutes, and it takes you :4 minutes to ascend plus your 1 minute deep stop and 3 minutes safety stop.... add it all up and you got about 20 minutes Total Run Time. So, where did the other 6'ish minutes go? If it was spent anywhere between 1 and 117' then it wasn't a "true square profile".

---------- Post added June 5th, 2013 at 09:41 AM ----------

At any rate...
There are two ways to do this dive. The correct way, and the wrong way. Guess which one is safer.

 

[chrpai]

I tried to do the math to give him very conservative ascent rates and extended stop times but ya... the math doesn't add up.

To do 118' (120') on AIR with 3-4min left in NDL would be a BT of 9-10minutes. Travel time from 120 - 0 at 30fpm is 4 minutes. Add in a 1 min deep stop and 3+ safety stop (let's call it 5 minutes) and we are looking at a 20 minute total dive time profile. I'm not sure where those other 6 minutes are. If we use 9 BT and 3 SS it's 17 minutes and 9 minutes are unaccounted for.

Either he went past NDL and did a little deco or he extended the ascent to the point that it's really a multilevel dive. Or is there another possibility that I'm not considering?

 

[rhwestfall]

profiles off back-up....

Not in the purest context, but square in my realm... not at all like exploring a wall or reef with much more levels...

 

[rhwestfall]

These are not square profiles. You said you did 118' for an RT of :26 minutes and left with 3-4 minutes of NDL? On Air? Not possible with a square profile. A square profile would mean you descended to 118' and stayed at 118' for 10'ish minutes (you said you still had 3-4 minutes of NDL) My tables show 120' good for :12 minutes.

So lets say you did 118' and it took you 2.5 minutes to reach depth...(using 45fpm to descend) you stay for 10 minutes, and it takes you :4 minutes to ascend plus your 1 minute deep stop and 3 minutes safety stop.... add it all up and you got about 20 minutes Total Run Time. So, where did the other 6'ish minutes go? If it was spent anywhere between 1 and 117' then it wasn't a "true square profile".

---------- Post added June 5th, 2013 at 09:41 AM ----------

At any rate...
There are two ways to do this dive. The correct way, and the wrong way. Guess which one is safer.

No, I said it was 118' max, and 26 min total dive time, and it was 99' max and 28 minutes total dive time.....