Do you turn the air off or leave it on after setting up on a tank?

[Shasta_man]

Related clarification: Can someone summarize the benefit of doubles for diving within recreational dive depth limits? I can see redundancy and if diving shallower the additional gas could extend your dive time beyond a single tank but otherwise?

 

[Boarderguy]

Related clarification: Can someone summarize the benefit of doubles for diving within recreational dive depth limits? I can see redundancy and if diving shallower the additional gas could extend your dive time beyond a single tank but otherwise?

Depth is irrelevant. Doubles extends time provides redundancy making for a "safer" dive. If you're staying above 130 fsw you'll still very likely cross into deco unless you have lp 50s on your back.

 

[Beau Holden]

Can someone summarize the benefit of doubles for diving within recreational dive depth limits?

Always diving the same configuration. A dive above recreational dive depth limits can be a purposed Deco dive.
Not changing tanks after a dive.
Never having to wear additional weights (lead)
As you mentioned - redundancy
Keeping the tank multiplying to a minimum.
Fits with the diving I do in my location.
Easier to carry entire rig on my back when walking to entry or boat dock (some people prefer side mount for this)

the additional gas could extend your dive time beyond a single tank

Depending on the tanks like HP80 you really don't have that much gas over two AL80s. LP tanks with cave fills are different. However, if doing boat dives I dive the boat rules regardless of remaining gas.

 

[BlueTrin]

Related clarification: Can someone summarize the benefit of doubles for diving within recreational dive depth limits? I can see redundancy and if diving shallower the additional gas could extend your dive time beyond a single tank but otherwise?

Another benefit is that they are quite stable in the water.

 

[Lorenzoid]

I agree with most of @Beau Holden 's reasoning. I would omit redundancy, though--at least for the kind of recreational diving I do. In my mind, if it's a recreational dive, a failure means I end the dive and ascend as expediently as possible. I would do that on a recreational doubles dive. Mind you, I'm not a cold-water diver, and I suppose there could be a greater need for redundancy if reg freeze-up is a potential problem.

 

[SlugLife]

Now, for all I know he may have been there that day to practice valve drills

Without taking to that diver, it's hard to say exactly what he was doing. However, if he was practicing, usually my preferred method (and I'll do this solo) is find a gently sloping shore and practice skills or equipment in standing-height water. When I'm feeling more confident and comfortable, I'll go out a little further.

Related clarification: Can someone summarize the benefit of doubles for diving within recreational dive depth limits? I can see redundancy and if diving shallower the additional gas could extend your dive time beyond a single tank but otherwise?

I dive side-mount, not exactly doubles, but close. My reasons are:

• Redundancy. Two completely independent air sources. (#1 reason)
• Able to remove tanks, before climbing a ladder.
  • For some people diving with 2 smaller tanks, and the ability to remove tanks is important for back, knee, joint, etc problems.
• SideMount is fun, balanced, and a lot of small benefits (I'll save that for another topic)
• Able to do longer and/or deeper dives.
• Able to use the remainder of partially-full tanks.