tech talk

Text and illustrations courtesy of Steve Lewis. Underwater photos by Larry Cohen and Olga Torrey One of the least mysterious things about is how to rig a set of steel pri- mary cylinders so they hang at diver’s sides as they are sup- posed to, rather than hanging pendulum-like below them. However, some still struggle to get it anywhere close to right. Perhaps this article will help.

There may be several variations on the basic theme, but I have found the simple way to rig steel cylinders to hang this way is to break the process of rigging them into a series of simple steps. Now, before SidemountGetting Sidemount Tanks to Behave Tanks Themselves & Sit Where They Should

LARRY COHEN

explaining things in detail, there are a few Armadillo SM harness used them as stan- In it, is able to hold good hori- assumptions that apply to this method. dard, and some call them loop bungees. zontal trim with her or his cylinders parallel Firstly, the primary cylinders are fitted with These tips may not work with ring bungees with an imaginary line drawn through the left and right DIN type valves. Secondly, or straight bungees: Frankly, I have no idea centre of the diver’s body. whatever SM harness you use, it is fitted with since I use loop bungees exclusively. The The fourth and final assumption is that the loop bungees. Some folks refer to these third assumption is that you want the orien- bottom of the cylinders (the part nearest as “old school” bungees, some call them tation of your cylinders to look something the diver’s bum) are going to be clipped to ILLUSTRATION COURTESY OF STEVE LEWIS “Armadillo” bungees because the original like the illustration (Figure 1, left). hardware on the back of the SM harness or Figure 1. Desired sidemount cylinder alignment and balance point

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Figure 2. CAM band and stern achor whether or not the first stages are worn each affects at pointing in towards the diver or pointing least. out to the environment, is immaterial. When we dive sidemount, we A simple way to want our primary approach tank rigging cylinders at our Start with the notion that there are several sides, with the things that will affect a tank’s orientation, handwheels poin- and therefore, the diver’s orientation also. ting away from I find it easiest to get all of these things our bodies, and (let’s call them variables) approximately pointing very slight- squared away on dryland and then resol- ly down towards ve them one at a time, working in shallow the seabed, lake water with an observant buddy or one bottom, cave floor, with a GoPro and time to spare. etc. We want the The first thing to get sorted is the rigging handwheels ori-

on both tanks. The clip or boltsnap on ented this way to OLGA TORREY the neck of the tank is simply tied onto make it possible for a small loop of equipment line (3mm loop bungees to wrap around the hand- position of the handwheel “knob” is out (Figure 2, left) should make this clearer. braided poly works fine). The loop needs wheel and stay in place. We can do this and down. It shows a dotted line running along the to be long enough to allow it to fit over by manipulating the location of where Start off by looking at the cylinder cylinder at 180 degrees from and oppo- the valve and handwheel. This clip is a the cord with a on it is conne- from directly above. Think of the hand- site to the handwheel. The CAM band backup for the loop bungee, so its setup cted to the body of the primary cylinder, wheel pointing to 12 o’clock on an is shown in red, and the tail (a piece of and configuration are probably the simp- in such a way that the natural resting imaginary (and analog) clock face. nylon equipment chord) and the bolt lest things about rig- Six o’clock is snap or butterfly clip is shown as a solid ging sidemount. opposite and black line with a small black and red It is the placement of at 180 degrees oval at the end of it. the stern (rear) anchor away from it, For the vast majority of divers, fixing the point in relation to the and we want stern anchor point at six o’clock (or slight- position of the valve— to mark this ly to the left or right, let’s say, five-thirty well, the handwheel line. So, take a to seven-thirty) will greatly help orient the on the valve, that is a straight-edge bottle and handwheel correctly. In fact, little more complex. I and a marker the best option is to start off with the guess we could start and draw a line anchor point at six o’clock for both the anywhere, but I seem about 20cm left and right-hand cylinders. Fix them in to have the best or eight inches this way, and let’s move on. luck, and the shortest long from the Now, note well a couple of provisos. gear-tweaking sessions, bottom of the The distance of the CAM band from the

ILLUSTRATION COURTESY OF STEVE LEWIS starting at this point. tank along this bottom of the cylinder is another varia- First of all, it helps if six o’clock meri- ble and something we will discuss in a somewhere close to the diver’s hip. we understand what dian along the few paragraphs. At this point and as a A fifth point, not really an assumption, is challenge we are try- side of each first step, all we need to do is to find the that as long as tanks with opposing valves ing to “fix” with each cylinder. optimal spot on the clock face to fix the are used (i.e. left and right-hand valves), variable—or what ILLUSTRATION COURTESY OF STEVE LEWIS The illustration spot where the stern anchor is attached

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Figure 3. Variables on sidemount tank rigging

ILLUSTRATION COURTESY OF STEVE LEWIS

Okay, with that shoulder. Making it longer or shorter done, we are allows a diver to adjust the position of the ready to work valve and cylinder’s top with the diver’s on the rest of chest and armpit. our tank rigging. If the loop bungee is too long, the The illustration result will be a bottle hanging low in the above (Figure front and higher in the back. If the bun- 3) shows three gee is too short, the diver will be unable more primary to reach the tank handwheel, and there ILLUSTRATION COURTESY OF STEVE LEWIS variables. is a good chance the valve will dig into his or her armpit. This is both uncomfor- to the cylinder. Point A is the length of the loop bun- table, and potentially hazardous since For the time-being, we can put the gee that wraps around the cylinder’s he or she will most likely not to have CAM bands three or four fingers width handwheel, keeping the top of the tank the mobility to doff or don the cylinder from the bottom shoulder of our cylinder. attached to and aligned with the diver’s without help. Most manufacturers of loop bungees use 6-7mm (1/4-inch) thick shock cord. This thickness is strong enough not to stretch much in water. Bearing this in mind, adjust the length of your loop bun- gee so that with your arms by your side, and without any tension in it, the end of the loop just pokes out past your bicep. This will need to be fine-tuned for some

LARRY COHEN

individuals but it point (either a Dring or “door handle” is an okay star- on the diver’s harness, or on the diver’s ting point. waistband). We have already oriented the anchor point to align the handwhe- Point B is the els, which is controlled by making this the length of the cylinder to hang parallel to our lateral tail attaching line. If the tail is too long, the cylinder will the cylinder’s be oriented tail down. Too short and it bottom to the will be difficult to handle, and the tank

ILLUSTRATION COURTESY OF STEVE LEWIS stern anchor will sit with its bum pointing up instead of LARRY COHEN

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straight back. head or bum down—you move about 10cm. This makes fine-tu- The length of this tail WILL need the CAM band towards whichever ning my trim easier when I wear to be adjusted! Do not cut it too end of the diver is sinking. thicker or thinner drysuit undies. short when you first attach it to I find it much better and quick- There are more subtle issu- your CAM band. er to make small adjustments to es with getting your sidemount one variable at a time, and to self-squared away (hose routing, Point C is the location of the CAM get it “right” before moving on. for example), but this should help band or clamp attaching the Your mileage may vary, but this you improve the way you look stern anchor to the cylinder. This method works for me. and feel in the water. is one of the factors influencing A few centimetres of adjust- The value of a buddy with a the diver’s trim! Moving the CAM ment (an inch or so) can radical- camera who can photograph band closer to the top of the cylin- ly alter the trim of a tank or the you underwater, so that you can der will shift towards the diver. When you move something, see exactly what you and your diver’s bum, while moving it clo- make a note of what you did. I gear look like in the water, cannot ser to the bottom will shift weight also mark the ”six o’clock line” be over-stated—make it happen. towards the diver’s shoulders and on my primary cylinders with hash head. So moving the CAM band marks every centimetre or so Good luck.  helps to trim the diver who is either from the bottom of the tank up to Steve Lewis is a British diver, instructor, dive OLGA TORREY industry consultant and author based in Cana- make us better divers than we are da. He teaches and now. His latest book, Staying Alive: lectures at home and Techniques for abroad. His main focus Advanced , is avai- is dive safety and to lable through Amazon. For more make each of us aware information, visit: techdivertra- of the things that will ining.org or ccrcave.training.

ILLUSTRATION COURTESY OF STEVE LEWIS

ILLUSTRATION COURTESY OF STEVE LEWIS

OLGA TORREY

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