• Roger

Getting Things to Line Up Just Right

Updated: Apr 25

I like sidemount. I talk a lot of shit about it. But I do like it. It can be comfortable and streamlined. It can be very flexible. There is an argument to be made for completely isolated redundancy. Mostly it’s good for moving through places no bigger than the space below your coffee table. But it isn’t, as has been lamentably sold with such popularity, just as easy as buying a new harness and putting two tanks on your side. There are a ton of harnesses on the market which, mostly, each have their benefits and drawbacks. Some are more heavily weighted on the benefits side; some are complete crap. For all of them it is going to depend pretty heavily on your body type, philosophies, preferred tanks, and diving style. Most importantly, contrary to what anyone might tell you, there is no perfect system. I am not going to write any further on the various systems out there but to say if you are curious about the variety you can check Andy Davis’ blog HERE where he has meticulously maintained a listing of just about everything you can find on the mainstream market. Obviously only a small handful of those are seen in great numbers, but it is interesting to see the various trends and ideas. There is also a great deal of conversation about how valves should sit (ie: regulators “down,” valve faces pointing in front of you, or regulators “up,” pointing behind you - there is even a modified version where the valve handles point straight down with your regs inward toward your body). There are pros and cons to each of these as well, but I’m not going to discuss that here any further beyond saying, “Wear your regs up, dammit.” What I wanted to write about is something that I see people struggle with the most: getting your sidemount tanks to actually sit at your sides. You see how well the tanks lay in this pretty picture by SJ Alice Bennett?

Valves in the armpits. Tank perfectly parallel to the body along a line from the shoulder to the knee. Not breaking above or below the profile of the body. Regs and valves completely protected by your body both from damage and from water disturbance to create a wide, hydrodynamic platform. That. That’s what you’re looking for. Not this, which all-too-commonly seen.

Like the profile of a manta ray trying to hump a drowning anteater's leg. So... yeah. Let's not do that.

This is what we're aiming for.

How we do that is one of the reasons that sidemount is a giant asshole. Because it takes a handful of adjustments which are all fussy, completely dependent on your personal frame, and for which even single centimeters matter. In the shortest possible form, there are only two things that need to be adjusted, but they each have a couple of sub-sections. Boltsnap- - Height - Leash length - Angle Tank Neck Bungee - Height - Loop length - Strength Seems easy, right? It is. And shouldn’t take but at least a half-dozen dives under supervision with some video feedback followed by fine-tuning with systematic minor adjustments after each dive to get it just right. But if you’re one of those people who either decided they’re going to figure it out on their own (stop it, take a proper class), or if after your training you’re noticing that something either feels or looks off or uncomfortable let’s get started. One more thing I want to say from the get-go: there is no way for me to cover, in a blog post, every nuance of how things get perfectly dialed in, there are far too many variables. One of the biggest is steels vs. AL. The former just hang there where you clip them like a particularly somnolent sloth, whereas the later you will need to reclip to a set of d-rings further towards your belly, perhaps several times, or need sliding d-rings to compensate for buoyancy shift. Honestly, steels are easier. In any case, think of this more as a troubleshooting guide using AL80s as a basis.


Height- This is the first place to start and, arguably, the easiest and most obvious thing to adjust.

In these pictures there are a couple of exaggerated band heights. Very simply, however high the band is on the tank is going to determine, in large part, how high or low on your body the tank is going to rest. This is going to depend, too, on whether you are using some version of a butt-plate or clipping the tanks to your waist.

In any case you can start with a tape measure.

Measure the distance from comfortably into your armpit down to where you expect to make your attachment point, either waist-belt or butt-plate. Then measure from the very top of the tank valve down and put a sharpie-mark on the tank at the same distance.

There. That’s your band height starting point.

Leash Length-

The leash is the little dongle of static line that attaches your boltsnap through the airplane clamp.

Here you see a long one and a short one.

(Note: pointing up or down doesn’t matter - just make sure they’re the same way round on both tanks or your boltsnaps will be just different heights enough to be really bloody annoying.) This, too, is fairly easy. It’s the distance from your attachment point down to where you want the tank to sit. I said I was going to mention steels in passing, well here it is. As I mentioned, most steels tend to stay put, buoyancy-wise. If you’re using steels, you’re probably using a butt-plate which means you’re going to need longer leashes. Start with 3 inches or so (longer if you’ve got big hips, shorter if you’re narrow) and then fine-tune as you see how your tanks sit. Once that’s done, you’re done; clip them and dive.

If you’re using ALs you are probably going to want the leashes as short as possible to keep the tanks under tighter control. Aaaaaand, that’s it for leash length. Angle- What I mean is, where around the tank does the bolt-snap sit.

You’ve got a little bit of wiggle room, but a great place to start is at about that 45 degree angle between the very back of the valve and the bolted isolator post. This is another thing that is going to vary quite a bit depending on personal taste, body shape, and how hemmed in against your hips you like your tanks. Closer to the 9:00/3:00 positions will give you a little more room if you like, or if you are a hippy-er person. Closer to the 12:00 position is better if you are narrow framed or if you like everything really secure-feeling. One additional thing of note here is that the further to the 12:00 position the snaps are, it may be a little more difficult to argue with the bungee torque when you reclip the tanks as they are breathed down. The big thing to remember, is to have them mirrored.

A last, short note about steels. Because you don't need to counteract any bungee forces (you'll see what I'm talking about below) you can put the attachment point on the valve side of the tank. You can also just loop the bungee over the valve handle and be done with it. There are also a few harnesses that require this or even a reg down configuration. Some people simply like it. They're weird.


Height- If you have the bungee pulling from a point right at the base of your neck that is going to affect where the tanks want to go as the bungees try to relax. Similarly, you don’t want your bungee attachment points down in the very middle of your back. Right between your shoulder blades. There. Done. That’s where your bungees should be pulling from, so anchor them there. Some systems are inflexible about where this anchor point is and some are super adaptable. Then there are aftermarket bits you can buy to create your anchor point wherever you want. This can also be done with a triglide and a piece of string. Loop Length & Strength- These go hand in hand. A good starting point is that the bungee loops, without tension, hit dead center of your armpit. That should be where the bungee “relaxes” to when you’ve got the tank attached. Stiffer bungee might need a little more length, “boingier” bungee you can get away with quite a lot of slop. I strongly recommend the later because it makes gearing up that much easier and it does not take a lot of force to control the near-neutral AL80s anyway. There is a point of diminishing returns for each, though. Bungee that is too boingy and left too long will allow the tank to wobbly around like a shopping cart with a stiff wheel on your side. Stiff bungee that is kept too tight will rotate the handle (and the tank) in such a way that it’s difficult to reach or manage. Length and strength is one of those places you’re just going to have to play around a bit to hit the sweet spot of where you like it. Strength, unfortunately, might be limited to what is available at shops near you. Length, however, is much easier to play around with; it’s even easy enough to get your buddy to adjust even in the water. Just don’t tie tight stopper knots until you get it just right. With all of this in mind, what you’re looking to balance out are these forces

The attachment point towards the body and the bungee torque away from it are in direct contradiction. As are, obviously, positive and negative buoyancy. Let’s look at some of the ways an imbalance of these forces may manifest.


This is one of the simplest and most common problems. The tank base is just riding too high.

Could be that you've configured your harness with the initial clip point way too far back. More likely you're just a little ways into the dive and need to reclip. The buoyancy has started to shift positive as the tank has been breathed down and you can use either a sliding d-ring or another attachment point on your waist to pull the whole butt down.


Looks kinda the same, but it ain't.

Your bungees are too long. Or maybe not boingy enough. Tank valves are probably pointing straight down because the tanks are hanging limply in that wet noodle of a bungee. Either way, if you get the valve up by tightening up that bungee a bit, then you're in great shape.

This is one of those things you can remember you wanted to do after the last dive and ask your buddy to come back with you to the surface to correct before you start in earnest.

With a really good buddy and a lot of flailing, maybe you can get that shit fixed without surfacing.

This is the opposite of that first picture. You've got your initial clip point configured too far forward. Or, maybe, you've reclipped too soon.

There's a tricky, in-between period, if you're only using two sets of attachment points to change forward during a dive. Between about 2600-2300 psi (180-150 bar) where the ass floats up at the initial point and down at the front attachment point. If you hate this it's time to get a third set of d-rings or sliding d-rings. Getting those d-rings in just the right places along the waist strap can be a confusing exercise. You'll look at two of them and say, "There's barely space to fit a third in the middle! Why should it make such a difference from one to the other!?" But it does.

(Honestly, I have taken to using sliding d-rings because I don't even like the in-between periods with three rings.) Worth note that it is less likely, but this may also be, in part, because your bungee anchor point is too high up your back and it's trying to pull your regs up to the back of your head.

Tank bands are way too low and push the whole tank up past your armpit.

You won't be able to use your arms. Your hoses will be all over the place. There's not a chance in hell you'll be able to reclip because you're going to have to play tug-of-war with the bungee while you both unclip and try to reclip the boltsnap.

This is no fun.

Tank band can be too high up the tank, too. The tell-tale sign of this is that every time you kick it feels like both tanks are waggling behind you like an unbalanced U-Haul trailer. Also, to reach your tank valves it will feel like you are trying to fish something out of the back pocket of a pair of jeans that is too big. This can often happen in conjunction with or simply because the tank bungee anchor is too low down your back. Remember: between the shoulder blades. Tighten it up.

OK, too tight! You've gotten really ambitious about having everything on lockdown. I bet you tie your shoelaces to the point just before you lose circulation in your toes. Either that or you're just trying to convince your sidemount tanks to spontaneously become backmounted doubles. If you just really can not reach your tank valves it's because the force of the bungee is overriding the anchor of the clip and pulling the tank valve knob to point straight behind you. You probably can't reclip either - again, because trying to manipulate the clip is going to be a losing war against mega-bungee. Probably feel like you can't kick because your tanks are holding your legs together... Calm down. Loosen up. Listen to some Dead or something. Raise the bands a little. Loosen the bungees. It's OK. It's just scuba diving. (I do actually wear my CCR bailout this way because it is super out of the way. But I also have orangutan arms and can still manipulate my valves perfectly easily. I don't recommend it.) This is also a "maybe the bungee anchor is a little too high" moment. But even then... sheesh, take it down a few notches.

So this one isn't actually a disaster. There are some harnesses designed specifically so that the tanks will ride like this. Which... meh. OK, I guess. They're protected. They're streamlined. They're easy to safely manipulate and operate. And they don't change your profile... too much... I guess? I tend to think of this as front-mounted, though. There is such a thing as too-chill. Get your act together hippie.


I am bored and hate the coronavirus. I would rather be diving. But I still like talking about diving and figured that was an alright way to spend a day.

I hope that if you've made it this far through today's ramblings that you've either learned something, thought of a new way to convey some of these ideas to your friends/students/dive buddies/people who don't care about diving but you talk at them about it anyway/or dog who is the only other person currently on quarantine with you. If there is any actual point beyond, "Roger killing a bunch of time," let it be this: As you are dialing in a sidemount system, make only one adjustment at a time. Seriously, centimeters at a time; a full inch can frequently knock you too far in the other direction. Have a friend shoot a bit of video of you so you can see how the tanks look so you can match that up with how they feel. Stay safe, stay healthy, let's go diving together soon.

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