Sidemount Question

[Selachimorpha]

This is a question from a non-cave diver, just curious as to how there things work. If you have tanks on your sides instead of on your back, then they are independent, rather than connected by a mannifold as backmounted doubles normally are. So my question is, if you are breathing off one of the tanks, as the gas is depleted that tank would become less negative. So how does it work in terms of balance, do you breathe some of one tank, then some of the other?
I guess you could ask the same question about back mounted doubles that are independent, although I would have thought that your balance is less affected if one side is emptier than the other, compared to sidemount, where the tanks are further from the center of your body.

 

[InkDiver]

So how does it work in terms of balance, do you breathe some of one tank, then some of the other?

exactly...but it's not just about balance, it is also about gas management. you don't want all your eggs in one basket if you should have a failure or need to donate.

 

[Dive-aholic]

It's about both gas management and balance. The size tanks I'm diving dictates when I switch regs. In my 108s I have to keep my pressures within 500psi of each other or else I start to lean to the heavy side. The most difference I'll ever allow between tanks is 1/6 of my starting gas. If I lose the use of one of my tanks, I want to have enough air in the other one to get me out of the cave. This is also the reason I never dive to 1/3s. Losing air in a tank will not allow me to get out if I'm pushing the limits that much.

 

[BgDadddy]

Ditto. I switch tanks every 500 PSI so they are always close to one another.

If you breathe one down to 1/3 on the way in and lose all your gas in the other one, you've got a big problem. Keep the volume balanced throughout the dive.

 

[Cave Bum]

Hummm, I don't do it that way. I breath one tank down to 1/3 then switch to the other. I don't find enough of a difference to matter, they're both still negative at that point (LP95's). BTW, I breath the long hose tank first. (I have a long 5' hose on my right tank so I can donate a reg in an OOA situation while we're setting up to switch tanks...) That way when I switch to the short hose left tank, I'm on it until I breath down 2/3's.

In flying we used to switch tanks every hour to balance the load, but I've never found it necessary in sidemounting...

 

[Jeff Toorish]

All the answers here have been great --I breath down 500 PSI in the first tank, then 1000 PSI in the second tank, then back to the first tank for the next 1000 PSI --turning at thirds of course.

Incidentally, you do not have to use a manifold when diving back mounted doubles. My back mounted doubles are independent and I use the same pattern when diving them.

I've never really noticed any big difference in trim or buoyancy with either sidemount or backmount independents.

Jeff

 

[Dive-aholic]

Hummm, I don't do it that way. I breath one tank down to 1/3 then switch to the other. I don't find enough of a difference to matter, they're both still negative at that point (LP95's). BTW, I breath the long hose tank first. (I have a long 5' hose on my right tank so I can donate a reg in an OOA situation while we're setting up to switch tanks...) That way when I switch to the short hose left tank, I'm on it until I breath down 2/3's.

In flying we used to switch tanks every hour to balance the load, but I've never found it necessary in sidemounting...

While many of us switch for balance in the rig, the main reason for keeping the pressures within 1/6 of each other is safety, especially when diving solo or in a mixed team.

 

[BgDadddy]

While many of us switch for balance in the rig, the main reason for keeping the pressures within 1/6 of each other is safety, especially when diving solo or in a mixed team.

Exactly! The weight isn't the issue. The issue is what happens if you lose the full tank while you're in the cave and all you have left in the remaining tank is 1/3.

 

[SuPrBuGmAn]

The weight can make a difference depending on the type of tank used. Generally, you want to keep the tanks closer to 1/6ths than 1/3rds to give you the best possible chance of exitting if you lose the gas from one tank or the other.

 

[K Mejean]

When you guys set up your side mount rigs do you have the bottles set up like a stage bottle. In referance to the way it clips on to your backplate/wing? I use a set of doubles for my back gas and have a couple of bottle set up for stages. I am just wondering if the clips are the same or if you have a different way of doing it.