Sidemount and nitrox mix

[scuba127]

I stand corrected. I got my Advanced Nitrox card probably 5 years ago and for some reason had it my head a shop would only give you 32% or 36% on a regular nitrox card....I didn't mean to put out bad info....thanks for correcting it....

 

[Jim Lapenta]

Are you going to take along only two tanks to be used for both dives- no refilling between dives? In that case, I'd probably do both on ean32 and be done with it. Otherwise, I'd use ean36 for the second dive.

In my opinion the difference between 36% and 38% is not worth the hassle...

Yes, I'm aware 32% at 130' yields ppo2 of 1.6, IMO for a single day of diving it's fine- that's what I usually dive...

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A ppo2 of 1.6 in 36-38 degree f water with less than stellar vis? Hopefully in a drysuit. 1.6 is not recommended for the working portion of the dive by any agency I am aware of. And for a newer diver. Whose physiology and experience you do not know.

Seems very irresponsible advice. Best practice in the Great Lakes on these types of dives is as I outlined earlier. Mix for the bottom of the deepest dive. Ppo2 max of 1.4 ( I won't go that high but I know my body). If you want to use a leaner mix for the shallower one buy two more more tanks and fill them with the appropriate mix for that dive.

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[rhwestfall]

Set your own two tanks up with the best mix for dive #1, and rent two additional tanks for dive #2 with the best mix for the dive....

 

[TONY CHANEY]

I really cannot believe what I have just read. Have we really gone this far from real classes with real instructors? The problem with this entire thread is OP is mistaking, Greatly Mistaking, side mount Vs stage or deco. Sidemount should be approached just like backmount doubles. You are using double tanks for 2 reasons 1) more gas and 2) redundancy. Both tanks should be matched because if one fails and you have to go to the other tank you don't make a mistake of jumping onto a hot mix and blowing pass 1.6 O2pp. I would hate to have to do the computer gas changes every time you switch regs. What you are really doing is monkey diving one tank and have another tank for God only knows what for. So if you really want to have different mixes you should just be diving a single tank backmounted.

 

[Jai Bar]

A ppo2 of 1.6 in 36-38 degree f water with less than stellar vis? Hopefully in a drysuit. 1.6 is not recommended for the working portion of the dive by any agency I am aware of. And for a newer diver. Whose physiology and experience you do not know.

Seems very irresponsible advice. Best practice in the Great Lakes on these types of dives is as I outlined earlier. Mix for the bottom of the deepest dive. Ppo2 max of 1.4 ( I won't go that high but I know my body). If you want to use a leaner mix for the shallower one buy two more more tanks and fill them with the appropriate mix for that dive.

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I probably failed to read in OP anything concerning such cold water and below stellar vis, as well as anything about great lakes and the such.

My apologies, I dive nothing less than warm tropical waters, stay away from anything below 25 degrees celsius and/or below 20m visibility.

Anyway, the original poster has a very weird way of asking questions, not explaining exactly what he wants or providing important information.

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[beanojones]

I really cannot believe what I have just read. Have we really gone this far from real classes with real instructors? The problem with this entire thread is OP is mistaking, Greatly Mistaking, side mount Vs stage or deco. Sidemount should be approached just like backmount doubles. You are using double tanks for 2 reasons 1) more gas and 2) redundancy. Both tanks should be matched because if one fails and you have to go to the other tank you don't make a mistake of jumping onto a hot mix and blowing pass 1.6 O2pp. I would hate to have to do the computer gas changes every time you switch regs. What you are really doing is monkey diving one tank and have another tank for God only knows what for. So if you really want to have different mixes you should just be diving a single tank backmounted.

But what one can do with sidemount that one cannot do with BM doubles is take three tanks on the boat, two with the bottom mix for the first and the other one to swap out for one of the first dive tanks on the second shallower dive.

Since this is exactly the kind of thing sidemount allows one to do (dive two sets of doubles with only three tanks) this is exactly the kind of question that only sidemounters might understand.

Three full-size tanks for a two tank boat dive is the kind of thing that sidemount (and only really sidemount) allows.

 

[stano]

+1 for what Tony said. Have you dove to 130' in the Great Lakes before. Two HP 100's where one is a mix for 80' (cant use on the dive) sounds like a great way to ace yourself. Sidemount (like doubles) is about having more available gas for yourself and your buddy. If one tank is MOD 80' what's the point?

 

[TONY CHANEY]

But what one can do with sidemount that one cannot do with BM doubles is take three tanks on the boat, two with the bottom mix for the first and the other one to swap out for one of the first dive tanks on the second shallower dive.

Since this is exactly the kind of thing sidemount allows one to do (dive two sets of doubles with only three tanks) this is exactly the kind of question that only sidemounters might understand.

Three full-size tanks for a two tank boat dive is the kind of thing that sidemount (and only really sidemount) allows.

you might would have a point if the OP was to include a third tank. He is just trying to do two dives, very different depths on only two tanks. You can also throw in the thought that if he / she uses both tanks during the first dive (switching back and forth) then you are starting out you second dive with one full tank and one tank not full. Not only are you starting out the dive out of trim (more to the point if it was Al tanks, but these are steel so not too much diference) but you also if you lost your full tank then you have to have enought gas in the tank used on the first dive. We could go on and on about the + and - of BM Vs SM but, there really is no point in doing that here.

 

[Superlyte27]

I don't think you should have an issue answering this question if you were nitrox certified. Maybe i'm just reading the question wrong, but what does this have to do with Sidemount?

You read my mind

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

I use 28% Nitrox for dives at 130' which requires an Advanced Nitrox Card to obtain the gas.....so, yeah, if at all possible I'd use nitrox for the 130' dive in order to increase bottom time....

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

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

Thanks so far for a input. Sorry for not being clear about all the information on my last post. I am planning to do those dives on the same tanks if possible. 2 HP 100 steels in the Great Lakes (cold fresh water). For 130 ft with ppO2 1.3 mix will be 26 but for 80ft is 38. So how do I adjust the mix when doing sidemount?

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 ----------

Are you going to take along only two tanks to be used for both dives- no refilling between dives? In that case, I'd probably do both on ean32 and be done with it. Otherwise, I'd use ean36 for the second dive.

In my opinion the difference between 36% and 38% is not worth the hassle...

Yes, I'm aware 32% at 130' yields ppo2 of 1.6, IMO for a single day of diving it's fine- that's what I usually dive...

Sent from my myTouch 4G

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 ----------

I probably failed to read in OP anything concerning such cold water and below stellar vis, as well as anything about great lakes and the such.

My apologies, I dive nothing less than warm tropical waters, stay away from anything below 25 degrees celsius and/or below 20m visibility.

Anyway, the original poster has a very weird way of asking questions, not explaining exactly what he wants or providing important information.

Sent from my myTouch 4G

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!!!

 

[TONY CHANEY]

Superlyte...thanks! I myself was so blown away I had to post. Oh and to add to what Superlyte just posted. That little inconvenience about losing a tank at 130' and getting up to 80' so you can use your other tank gets a little hard when you had the tank attached to your LPI on your BC. Better remember which tank is attached to the BC and which one attached to the DS.