Here’s a short video clip of me taking the stage bottle off and putting it back on during an actual dive in Twin Cave.
A few years back several of us were experimenting with different ways of carrying a stage cylinder with a sidemount configuration. Having already done dives in backmount with stage cylinders that method, carrying the stage cylinder below with the clips connected to the chest and waist D-rings, was the obvious first choice. However, this method detracted from the streamlining offered by a sidemount configuration.
Some divers over in the High Springs area were experimenting with mounting their stage cylinders on top so that the stage cylinder lay partially on top of one of the sidemount cylinders and partially on top of the torso. The way these cylinders were being connected to the sidemount rig was with the clips attached to the cylinder with bungee rather than the standard stage webbing. The bottom clip would attach to the butt plate bar and the top clip would attach to the chest D-ring on the same side.
We tried a few different methods of doing this. The first was to attempt to bring the top clip and bungee over the shoulder but that required quite a bit of flexibility, more than what is required to do valve shut downs in backmount. The next option was to try to route the top clip and bungee under the arm. This worked out well. It didn’t require as much flexibility and kept the top of the cylinder cinched down close to the diver’s body. The issue with this method was in keeping the bottom of the cylinder from floating up as the gas in that stage cylinder was breathed down.
With more experimentation it was found that stretching the attachment points on the stage cylinder did a bit to minimize this floating in the bottom of the cylinder but it did not eliminate it completely. The key to minimizing the bottom float is to position the attachment points so the cylinder is pulled down by this stretch. Some people have looked for a standard distance for the attachment points, or actually, where to mount the worm gear clamp that holds the bottom clip, but there just isn’t one. The positioning of the attachment points is dependent on how far apart the butt plate bar and chest D-ring are from each other. People with longer torsos will need to position the lower clip on the stage cylinder farther away from the cylinder neck and those with shorter torsos closer to the neck.
But regardless of where the clip is attached the bottom of the stage cylinder will still become positively buoyant and float up as gas is breathed down. The shorter the torso, the more of a problem this is because the bottom attachment point has to be farther from the bottom of the cylinder. This has caused many sidemount divers conducting cave stage dives to carry the stage cylinder on top during the penetration portion of the dive and to then clip the cylinder underneath during the exit portion so the cylinder rises up into the diver rather than onto the ceiling of the cave. This method does work to keep the cylinder off the ceiling but because the valve and 1st stage are so heavy, the top of the cylinder hangs low. An option to fix this is to add a second bungee loop to the rig that can be used to pull the top of the stage cylinder in close. This is a method I use when doing open ocean decompression dives where I keep my decompression cylinders with me throughout the dive.
One thing I won’t do is stage a decompression cylinder on top. A standard stage cylinder is usually used at the beginning of the cave dive so as you are attaching the stage to your rig you should already have the 2nd stage regulator in your hand and have followed the hose back to the cylinder and confirmed gas and MOD. Once the cylinder is mounted on top it is impossible for most to perform that confirmation of gas without taking the cylinder off. Most decompression cylinders are smaller diameter aluminum 40s. Taking these cylinders and mounting them underneath and using an additional bungee to bring them in closer allows for the proper procedure in gas switches and keeps them very streamlined.
Back to top mounting standard bottom mix stage cylinders. I never liked the fact that the bottom of the cylinder would become positive and increase the chance for contact with the cave ceiling. While this isn’t an issue in taller passages, not all passages are tall enough for that. And an AL80 that is angled off the torso at a 45 degree or more angle isn’t very streamlined. Every stage dive I did I would try to think of better ways of rigging a stage cylinder for top mounting. I’d much rather keep the stage cylinder on top but not at the risk of damaging the cave.
Well, recently I was able to come up with an idea that works very well and keeps the cylinder tucked in close to the body and parallel to the body throughout the entire dive regardless of the amount of gas in the cylinder. I even spent several dives going into sidemount restrictions and was able to keep my stage cylinder attached to me through most of them and still get through the restrictions. It was only the smallest of the restrictions where I had to remove the stage or my right side cylinder to get through.
The problem with the current sidemount stage configuration is that the bottom clip attaches to the back of the sidemount rig. As long as the attachment point is on the back, the cylinder will be allowed to pull up off the back. What I did was move the worm gear clamp holding the bottom clip down a bit. For me, because of my torso length and the distance from my chest D-ring to my butt plate bar the best location for the worm gear clamp with the system most often being used is about 19 inches from the bottom of the cylinder. That’s where my stage cylinder would remain the lowest throughout the dive.
I moved the worm gear clamp down to about 8 inches from the bottom and lengthened the bungee on that clip from almost nothing exposed under the clamp to 8 inches plus the clip.
When the bungees are the correct length the stage cylinder will lay on top of your sidemount cylinder and the bottom will not rise up at all regardless of cylinder pressure. If the cylinder does start to rise the most likely issue is you have the worm gear clamp positioned too high on the stage cylinder. The bungee could also be too long. If the stage cylinder rolls off the side of your sidemount cylinder then the bungees are too long. You will need to shorten the bungees a bit so the cylinder gets pulled into the space between your sidemount cylinder and your torso.
I’ve done several dives with this configuration and it is easy to put on and take off and keeps your rig streamlined throughout the entire dive. There is no reason to have to move the stage cylinder in front of you halfway through the dive and you don’t have to worry about the bottom of the cylinder hitting the ceiling. You will notice the left cylinder sits a little lower with the stage cylinder mounted on top of it. That’s okay. With a stage cylinder your profile will be a little higher from bottom to top. It doesn’t matter whether that extra profile is below you or above you, it will be there either way. For those of us who dive sidemount quite a bit, we’re used to having more clearance above us because we don’t have cylinders there so I’ve found it better for me to lose clearance below me rather than above me. If you want your sidemount cylinder to shift forward less then lengthen the bungees on the stage cylinder and it will shift up a little. Have fun trying this new method out and if you have any comments or suggestions please send them. I can’t think of an easier way to do this but that doesn’t mean there isn’t one!