Air Sharing/ S drills in sidemount

[rambaldi]

If everyone on the team is diving sidemount how can an OOG situation even occur? Why is rapid reg deployment even an issue?

Or if it does, is a long hose really the answer. Shouldn't you be donating and then switch tanks around? The reason for running a long hose is for a single file exit. There is no need for that if you can just switch tanks around. I would still want a longer than normal hose so you can both be comfortable while sorting things out but after that you should be able to exit normally. Note that this doesn't take into account people using (and weighting themselves) for oddball tanks within the team, and assumes you don't need to be single file during deployment.

 

[DevonDiver]

Or if it does, is a long hose really the answer. Shouldn't you be donating and then switch tanks around? The reason for running a long hose is for a single file exit. There is no need for that if you can just switch tanks around. I would still want a longer than normal hose so you can both be comfortable while sorting things out but after that you should be able to exit normally. Note that this doesn't take into account people using (and weighting themselves) for oddball tanks within the team, and assumes you don't need to be single file during deployment.

There are factors like silt-out and confined areas to consider. Swapping tanks wouldn't necessarily be the safer option, given certain circumstances.

I do agree with the previous though - running out of gas on sidemount is pretty hard... at least, running out without warning and needing a 'save-a-life' immediate gas donation.

 

[markmantei]

although i absolutely loved my experience trying side mount, this gas issue is what bothered me the most (compared to the idea of back mount doubles at least). i think using the rule of 1/3 in side mount doubles is pushing the limits. if you loose one tank due to a 1st stage failure for example, at/or near the deepest point of penetration, you will be lucky to have enough gas to exit and complete a safety stop. where as with the back mount set up, you can at least shut down the one reg but still have access to gas in both tanks.

Not really trying to turn this into a bm vs sm thread, but assuming that thirds is sufficient for the dive you are doing, the theory is 1/3 in, 1/3 out, 1/3 for emergency. If you are balancing your tanks correctly, at turn you will have 1/3 in each tank, leaving you with sufficient reserve to lose one complete tank even before taking team gas into account, and you should be able to exit without air sharing.

Additionally, depending on the failure, you have the option of switching 1st stages underwater or breathing from the tank valve, granted either being an option of last resort. SM gives you options that BM just does not have.

Mark

 

[rongoodman]

If you are balancing your tanks correctly, at turn you will have 1/3 in each tank, leaving you with sufficient reserve to lose one complete tank even before taking team gas into account, and you should be able to exit without air sharing.

I think you meant to say that at the turn, you will have 2/3 in each tank, theoretically leaving enough to exit on one if you lose the other. Sidemount does give you the option of swapping regulators too, if all else fails.

 

[rick00001967]

at the turn, you will have 2/3 in each tank, theoretically leaving enough to exit on one if you lose the other. Sidemount does give you the option of swapping regulators too, if all else fails.

"theoretically" being the operative word i guess. i think if i was using thirds (remembering that 1/3 is a "minimum" reserve) i would subtract maybe 500 lbs from my starting pressure as a buffer before calculating my turn pressure.
now swapping regs under water......that would be a new one for me. never seen that done. not sure i'd wanna be doin that. like you guys say, i guess that truly would be a last ditch effort.

---------- Post added February 3rd, 2014 at 12:43 PM ----------

why don't you simply use the same hose lengths on both tanks (5, 6, or 7 foot)

so is there anyone who does this ?? no matter what the reasoning is. just curious.

 

[shoredivr]

"theoretically" being the operative word i guess. i think if i was using thirds (remembering that 1/3 is a "minimum" reserve) i would subtract maybe 500 lbs from my starting pressure as a buffer before calculating my turn pressure.
now swapping regs under water......that would be a new one for me. never seen that done. not sure i'd wanna be doin that. like you guys say, i guess that truly would be a last ditch effort.

---------- Post added February 3rd, 2014 at 12:43 PM ----------



so is there anyone who does this ?? no matter what the reasoning is. just curious.

I took a course where we swapped a reg under (fresh) water. The usual caveat, reg will need servicing, and the reg in question on the course was due for servicing anyway.

As to two 5, 6, or 7 ft hoses, there is a side mount group on FB where members talk about their rigs, and two long hoses are used by some.

And the best resource for side mount gas management is here on page 86, an article by Steve Lewis on Sidemount in X-ray magazine. http://www.xray-mag.com/content/x-ray-mag-56

 

[markmantei]

I think you meant to say that at the turn, you will have 2/3 in each tank, theoretically leaving enough to exit on one if you lose the other. Sidemount does give you the option of swapping regulators too, if all else fails.

2/3rd's of the tank volume in each tank, but 1/3 of of total gas supply in each tank. I guess I could have worded that better.

Maybe I can illustrate better by talking volume instead of pressure. If you have twin 120's filled to capacity, your total gas volume is 240cuft. That gives you 80cuft for ingress, 80cuft for egress and 80cuft for reserve. If you balance your tanks properly, at turn you should you have consumed 40cuft from each tank, and have 80cuft remaining in each tank. If you lose either tank at max penetration, you will still have 1/3 of your starting gas supply.

---------- Post added February 3rd, 2014 at 02:43 PM ----------

"theoretically" being the operative word i guess. i think if i was using thirds (remembering that 1/3 is a "minimum" reserve) i would subtract maybe 500 lbs from my starting pressure as a buffer before calculating my turn pressure.

There are many reasons why thirds may not be sufficient when dealing with an overhead (physical or virtual). There are many threads dealing with calculating reserves, or even better, take a tec course. Dissimilar equipment and SAC's in the dive team are two biggies right off the bat, and a simplistic (starting pressure -500)/3 may not be sufficient to accommodate the differences.

 

[tphelps]

On my sidemount rig, I have a short hose on the tank on my left side coming around my neck and to a bungeed necklace, also zip tied to the necklace. On the right side I have a 7 foot hose with the extra tucked into tank bungees, it comes around my neck also and is either in my mouth or clipped off on a shoulder d ring when I'm breathing off the other tank.

I can see an OOA emergency or S drill not being a problem if I'm breathing off the tank with the long hose, the problem I see is what if I need to share air while I'm breathing off the left side tank. If my buddy suddenly needs air and had to grab for a reg, the one in my mouth would be on the necklace and a very short hose, the right hand tank reg would be inconveniently clipped off to the d ring. In a low or no vis situation in an overhead that might make it even impossible to find for him.

Should I remove the zip tie on the necklace so the short hose can break away so he can grab the one in my mouth and then we can deal with unclipping the long hose while he suckles on the short hose and I hold my breath?

I guess I'm asking how you guys handle air sharing or OOA's with a clipped off primary (long) hose?

Maybe I can help, I'm a sidemount instructor.
In an OOG (Out Of Gas) scenario while you are breathing off the left post (your necklace), I teach my students to donate their long hose to the buddy.
My system is configured in the same way but I have a break-away on my long hose. To do this, fold an O-ring back along itself in a loop around the bolt snap and then zip-tie the O-ring to the end of your long hose 2nd stage.

IF the buddy comes up to you and tried to pull the reg out of your mouth, treat the situation from a Rescue Diver POV. Block the buddy with a straight left arm so he doesn't rip the reg out of your mouth meanwhile un-clipping your long hose with the right hand. Then in one motion, deliver the long hose to the OOG diver.

I teach all my sidemount divers to practice, practice, practice un-clipping their long hose. You should not have to look for it, it becomes muscle memory. But you need to practice often to maintain that dexterity and motion. That's why it is a good idea to do an S-drill whenever you are diving with someone new to you. But the short hose is NOT meant to be shared with another diver because it's a... short hose.

But I totally agree with what Jim said. Communication is vital and one should not encourage their buddy to "rip" the regulator out of your mouth. If he cant give an OOG sign then at least he should break away your long hose clipped off.

 

[SanDiegoSidemount]

so is there anyone who does this ?? no matter what the reasoning is. just curious.

Here's a proposal from DevonDiver himself:

http://www.scubaboard.com/forums/si...mount-isolatable-manifold-3.html#post_6836629

Not sure if this is still just spitballing, or if it's evolved into a configuration that some actually use.

 

[rick00001967]

Here's a proposal from DevonDiver himself:

http://www.scubaboard.com/forums/si...mount-isolatable-manifold-3.html#post_6836629

Not sure if this is still just spitballing, or if it's evolved into a configuration that some actually use.

interesting. thx for that. devondivers post in that thread is exactly what i was suggesting earlier in this thread. maybe i'm not crazy after all. lol