Is sidemount gas planning really better for buddy diving?

[jj1987]

After playing around with side mount recently, I've put some thought into the pro's, con's, and washes compared to back mount. I've heard a few people state that side mount is better for gas planning with buddy teams even, and the more I think about this, the less sense it makes. At best, I can see it being a wash, but would enjoy some conversation on the topic.

Let's say we're doing a scooter dive in a a low flow cave. We're scootering with backgas (or side gas) only, no stages.

For tank draining, I'll use the stats given in the following URL, assuming a gas loss from a reg free flow at 231ft deep. These times are for an AL80, so doubles and big sm tanks would obviously take even longer.
http://www.cavediver.net/forum/showthread.php?t=10779

Diver A in backmount has a reg free flow, shuts down the post, 20 seconds, saving 79% of the gas he had at the time (admittedly, a little less than that since the gas leak possibly slows as pressure in the tank slows, but since the leak is past the first stage, it's not going to be all that far from linear).

Diver B in sidemount has a reg free flow, so I see two options-

• since he lacks a manifold, he has to breathe the tank down for the next 91 seconds. I say this because feathering a valve on a scooter just isn't a viable option, although maybe some can scooter with the light and handle on the same hand. If he does this, he 50% of his gas in 91 seconds.
• since he's in SM, I've heard many people state that he can swap regs, but with a scooter ride to get home, does he really want to risk losing the oring from the working reg and lose access to 100% of his gas? At this point, assuming they were diving 1/3rds, this precious time spent unsuccessfully messing with the reg caused them to no longer have enough gas to get 2 people out.

One key point I would like to hear comments on, is would anyone really screw around with broken gear in a cave? A fatality was believed to have been caused by that about a year ago (fixing broke gear instead of using working gear to exit), so personally I would focus on getting out ASAP, and trust my gas planning. I personally feel the risk in dropping an oring and losing precious time would be one greater than exiting the cave with only 1 tank and my buddy's reserves. I've heard this argument for side mount, so clearly some people disagree with my line of logic, I'd enjoy hearing why.

Obviously I can understand the logic for solo diving because it eliminates the (near statistically impossible) chance of losing over half your backgas at once, so please keep the comments in the context of a buddy dive.

[fixxervi6]

Why not have your buddy tow you out while you feather and get as much usable gas out of the free flowing cylinder as possible.

Even said, if you planned proper there is enough gas in the remaining cylinder to get you out.

[jj1987]

Why not have your buddy tow you out while you feather and get as much usable gas out of the free flowing cylinder as possible.

I'm not sure how towing someone who only has one free hand would work. At the very least, you're slowing the exit. I haven't attempted to tow or be tow'ed in SM, so I'll avoid commenting on that, but you present a possibility I hadn't thought of, thanks for the post.

Even said, if you planned proper there is enough gas in the remaining cylinder to get you out.

Agreed, as long as you don't try to fix the broken one and mess up. I'm guessing this is just something I've picked up in passing conversation from divers, I don't see a realistic scenario where anyone would do it, except maybe once you're back to deco. I have replaced an o2 reg with a stage reg before, but I don't think I'd do the same thing during the dive for the reasons mentioned.

[JDostal]

Agreed, as long as you don't try to fix the broken one and mess up. I'm guessing this is just something I've picked up in passing conversation from divers, I don't see a realistic scenario where anyone would do it, except maybe once you're back to deco. I have replaced an o2 reg with a stage reg before, but I don't think I'd do the same thing during the dive for the reasons mentioned.

Definitely not... no fixing gear at all. I don't scooter, but I have had one emergency in sidemount. My regulator LP hose blew right off the first stage (the swage failed and the hose blew off). Massive air loss, bubbles, roaring sound and very suddenly couldn't breathe. After putting my heart back into my chest I grabbed my other reg and got the F out of the cave. The though of messing around with stuff to fix it wasn't an option. Very urgent light signal and very emphatic thumbs up followed by motoring towards the exit. My buddies stayed near the whole way out.

What was nice, in this case, is that I had complete independence. I was not panicked (after the first minute rush anyway) and was really mentally reassured that I had enough gas to get me out.

The only thing I wonder about is the long hose thing. I know some guys are putting long hoses on their SM tanks so they can donate to a buddy easily but I'm not sure if the benefit outweighs the hassle of dealing with long hoses. In real sidemount diving (where it is actually needed) a buddy is basically no help anyway. Bigger cave...I dunno yet.

[FW]

Definitely not... no fixing gear at all.....

Depends on what is wrong. If you dragged a reg in the silt, and you can fix it by removing the exhaust T, and flicking the sand out of the valve, then you don't loose much time, and save a lot of gas. Trying to fix a freeflow may be over the top, though.

[JDostal]

Depends on what is wrong. If you dragged a reg in the silt, and you can fix it by removing the exhaust T, and flicking the sand out of the valve, then you don't loose much time, and save a lot of gas. Trying to fix a freeflow may be over the top, though.

Good call. I was thinking more along the lines of catastrophes.

[FW]

I could have missed it, but I didn't see anyone mentioning sharing with a buddy BEFORE you run your remaining tank totally empty. That way you don't have to try sharing air in restrictions, siltouts, etc.

[Brian Kakuk]

A side mount diver can easily feather a valve while riding a scooter. I've done it for practice and have even been able to lower my breathing rate to where I came out to the equivilent of thirds (I'm much more conservative than thirds on a scooter with only two cylinders). This was solo with a helmet light, but even if I had a hand held, it still throws enough light to see where I am going. This was back when I had a baby aquazepp. I would have no problem considering feathering into my dive plan while scootering....now feathering the valve on a set of independent backmounts while scootering.......did I just hear circus music?

Safe diving,

Brian

[Marchand]

I think the reg swapping come in to play with multiple failures. lets say your scooter and one of your first stages fail right as you hit thirds. You won't have enough gas to exit in the one bottle, so breathe it down and see how far you get. Now you need to decide if feathering the other one will get you out or if swapping the regs will be your best bet.

Another thing that people will do is put an H valve on one of the tanks with another first and second stage. With this setup if one of the regs on the H valved bottle quits then its no big deal, just shut the one off and use the other. If the reg on the other tank quits you can breathe off the H valved bottle while swapping regs.

[SuPrBuGmAn]

I would say its basically a wash, you're calling the dive either way and heading home and either setup should get you back to the exit with proper gas planning. Assuming the manifold shutdown went well on BM, he should exit with more gas without as much fiddling around throughout the dive itself.