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How To Set Up A Sidemount Harness

A lot of divers find setting up a sidemount harness to be confusing, even those with experience diving backmount style wings. Here’s my ultimate guide to setting up, sizing and configuring your sidemount harness.

This article deals with ‘Mexican cave’ (aka UK) style harness designs; as these are the ones that require the most knowledge and procedure to get right. These type of harnesses can be seen on many of the most popular sidemount systems, like the Razor 2.0, XDeep Stealth, Apeks-WSX, Diamond and many more. You can even build your own harness quite cheaply and easily using my instructions below.

For details on DIY sidemount harness construction, see HERE.

I’ve tried to keep this article quite ‘generic’, as there are specific details and differences on most ‘off-the-shelf’ sidemount harness systems. Think of it primarily in terms of key guiding principles for configuration.

I’ve also made all of my illustrations without showing the sidemount wing attached – it aids clarity. When putting together your sidemount system, obviously you’d need to attach the sidemount wing at an appropriate stage in the process.

Sidemount harness plates and webbing

Step 1 – The Shoulder Plate

This is always the first step in putting together any new harness. The top of the shoulder plate should be just below the C7 cervical vertebrae (aka ‘the prominent bone’ at the base of your neck).

If it’s any higher, it will press into your neck when you’re in good trim. Any lower and you’ll be slackening off your shoulder straps and losing some fit with the harness.

Sidemount Harness Set Up copyright 2019 Andy Davis

Step 2 – The Lumbar Plate

The lumbar plate should be positioned down, very low over the lumbar region of your spine. That’s the ‘flat’ area just immediately above the crease of your buttocks. If you have a knowledge of anatomy, then the bottom of the plate should be over the S2 vertebrae. A common error is to locate the lumbar plate far too high on the spine. That mistake probably arises from divers who are more accustomed to diving with solid metal backplates of a set length.

Once you’ve positioned both plates, get a friend to take the measurement between the two plates.
Using that measured distance, thread and secure the spine webbing between the plates. Thread the webbing through the slot in the plates and then secure it using weight belt retainers/ tri-glides (top and bottom)back along the main webbing.
With the webbing threaded, secured and adjusted; you can now hold the plates against your back to ensure you got the distance right.

You’d now also attach any spine weighting systems, if you were using them. Also, if you are using a loop bungee tri-glides on the spine webbing – position that now also.

The Razor sidemount system comes with a one-piece spine and crotch strap. That makes the setup a lot more problematic. You’d have to size and fit the crotch strap at this time (see directions in Step 7, below). Personally, I don’t like having one-piece spine/crotch webbing; I dive a Razor very often, but I replaced with a dedicated crotch strap and it’s set-up as per this article.

Step 3 – The Shoulder Webbing

Once the shoulder and lumbar plates are configured, you can progress to setting up the shoulder webbing. Some sidemount harness systems come with one-piece webbing (i.e. the Razor) and some come with individual shoulder and waist webbing components. Nonetheless, the order and approach remain the same.

There’s definitely a knack to threading the webbing through the plates and it’s easy to get confused between front and back, or to get twists in the webbing. So take it slowly and work methodically with everything laid out flat.

Lay the sidemount harness webbing flat, with the inside facing you.

The webbing enters from the inside on the left (as viewed) slot in the lumbar plate and comes back through the second slot. Now is the time to add a shoulder D-ring.

Route the webbing up to the shoulder plate and thread it through the slot on that side. Keep track of which side in the ‘inside’ of the webbing.

shoulder plate webbing setup copyright 2019 Andy Davis

The webbing passes through the slot and then doubles back on itself. Then route it back through the opposite slot. The diagram below shows the outside of the shoulder plate for clarification.

Now route the webbing back down to the lumbar plate and thread it through the first slot on the plate from the inside. Again, remember to keep track of which side of the webbing is ‘inwards’. Also, don’t forget to add your other shoulder D-ring at this time.

Finish off by threading the webbing back through the remaining slot; outside to inside.

It’s really easy to make a mistake and get the webbing twisted when doing this.

Once threaded through, it then routes off to the right (as viewed).

You should have threaded enough webbing through to the right side (left as worn) for it to reach (just below) your belly button, with maybe 6″ to spare to thread the belt buckle with. The remainder of the webbing should stay on the left side (right as worn).

Sidemount Set Up copyright 2019 Andy Davis

Before you go any further, make absolutely sure that you didn’t forget to add the shoulder D-rings and that they’re threaded onto the proper side of the webbing. This seems to be a common oversight that happens quite frequently.

Obviously, the D-rings themselves should be on the outside. The exact positioning will be done later.

This also applies if you use loop bungees with tri-glides or rubber o-ring on the shoulder strap. They would be fitted at the same time as the chest D-rings.

Once you’re sure that everything is where it should be, then it’s time to fit and adjust the shoulder webbing. Needless to say, it shouldn’t be too loose, or too tight. Remember to account for the exposure protection you’d be using on your dives when setting up your sidemount harness (or wear your drysuit/wetsuit when actually doing the fitting).

One common mistake is to adjust the shoulder straps too tight, which pulls up the lumbar plate (see above). The shoulder straps should be sized so that the spine webbing isn’t forced slack; and that the lumbar plate can hang naturally where you first positioned it.

The sidemount harness chest and waist straps should now be approximately sized, but you’ll probably still need to fine-tune them later with some in-water adjustments.

Want a PDF copy of these instructions? It’s in my eBook…

My comprehensive guide to sidemount configuration and development as a diver.

178 Pages. PDF format. Fully Illustrated. $25

Chapters include:

Sidemount history, design styles and cylinder principles
Harness and bungee setup and sizing
Configuring deco/stage cylinders
Diagnosing cylinder trim problems
Regulators and hardware
Training and skillset development

Purchase eBook here!

Sidemount harness hardware: D-rings & buckle

Step 4 – Adding the Waist Hardware

Now is the time to add your waist hardware. That’ll either be four D-rings, or a pair of sliding D-rings.

As an aside, I don’t recommend sliding D-rings in most circumstances. Add them later if specialist need demands it. They should never be used as an equipment fix to a skills problem: the skill typically being bolt-snap manipulation.

If you are fitting ‘off-set’ or (aka ‘square’) D-rings to attach a sidemount pouch, fit them first; right next to your lumbar plate on each side. If not, add the D-rings first on each side. Then finally add the belt buckle on the left side.

d-ring positions on sidemount waist belt

I much prefer sliding-type belt buckles. People also call them ‘roll pin’ buckles. They’re lightweight and much easier to cinch and tighten. Unlike a jacket BCD, or wing, you won’t need a quick release buckle with a sidemount harness. Sliding belt buckles are a great upgrade for any sidemount rig.

Be observant to ensure that your belt buckle is configured to be in the centreline of your stomach. If your harness is well configured so far, it should be sitting much lower than your belly button. Most people need it on, or just above, the pubic region of the abdomen.

Once you’re sure that your buckle is correctly located for when you’re wearing your exposure protection, you can trim off any excess webbing from the side. Leave maybe 4-6″ and secure that back along the inside of the waist strap using rubber loops. Many sidemount BCDs come with these loops provided; but if not, you can cut 1″ loops out of an old bicycle inner-tube.

Again, ensuring that you’ve got a good fit, you can now cut away surplus webbing from the right side of the waist strap. There should be enough length to run through the buckle with maybe 6″ protruding.

If you will be switching between drysuit and wetsuit, or are worried about future weight gain, you can leave a longer surplus of waistbelt webbing. That extra should be on the buckle side; folded back inside the waistbelt and secured together with rubber loops.

Don’t forget to burn and melt the ends of the webbing once you’ve cut it – otherwise it’ll fray annoyingly. Just run a lighter over it until it begins to melt and bubble, then press the end flat with something metal (not your fingers!).

The main elements of your sidemount harness are now mostly all configured. It should look like the illustration above.

Step 6 – Adjusting the Chest Hardware

At this time, you can adjust and properly locate the hardware already on your sidemount harness. Start with the shoulder D-rings:

The optimum location for the shoulder D-rings is just immediately below your collar bones. These D-rings are primarily for attaching stage or deco tanks, but also the long hose will clip to your left shoulder D-ring when not in use.

Trust me, you want these connections up and above any other clutter near your armpits and chest. It pays dividends with reducing task loading and also helps keep stage/deco cylinders better in trim, if used. It also keeps your long hose second stage out of your armpit and nearer to your chin.

If you need lower attachment points for bungee systems then fit separate ones at the optimum height on your shoulder webbing. You can use simple fixed tri-glide retainers to secure some 550 cord loops; or even semi-movable rubber o-rings.

I like using the o-ring style, especially with loop bungees. These are the same thick o-rings that come with XDeep Stealth sidemount BCDs for use as sliding D-rings. If you don’t have an XDeep, you can purchase these o-rings from most good plumbing suppliers – the size is 50 x 8 mm (diameter x thickness). For Americans, that’s approximately 2″ x 0.3″. You can find these easily on a Google search; they’re sold on Amazon, eBay etc…

If using Loop Bungees, you’ll want your bungee attachment points at the level of the armpit. The rear bungee attachment goes at the same height.

The rear attachment can be a simple tri-glide, or you can make a worthwhile investment in some custom hardware, such as Andrew Goring at SUMPUK makes. These are special tri-glides that are extended in length and have two holes on each side, specifically for loop bungee attachment

positioning sidemount bungees on the front shoulder straps

Step 7 – Adjusting the Waist Hardware

Now is a good time to get all your waist hardware properly located.

scuba diving equipment setupcopyright 2019 Andy Davis

The optimum location of the front and rear waist D-rings is dictated by two factors:

Your waistline size.
The length of the bolt-snap and leash used for the lower cylinder attachment.

You want your cylinders to trim out corresponding to your side torso mid-line. That’s the line that runs from your armpit, through your hip and to your knee… when you are in good trim. Simplistically, it’s where the stitching runs down the sides of a t-shirt.

setting up sidemount equipment for good cylinder trim

For more about cylinder trim, read HERE

To get the location approximately correct (pending minor in-water adjustments), clip your cylinder bolt-snap to each D-ring in turn; and adjust the D-ring location on the waist belt.

Move the D-ring until the bolt-snap leash touches the side torso mid-line. That’s where to locate your D-ring. Do this for each D-ring. You’ll notice that the D-rings should end up symmetrical on each side and also front-to-back.

This is one aspect that sliding D-rings make easier. But they can have some drawbacks later on.

Step 8 – The Crotch Strap

Unless you’re configuring an unmodified Razor system with a one-piece spine and crotch strap, you’ll now need to set up your crotch strap. It usually makes sense to leave this until nearer the end, as the crotch strap doesn’t affect any other fitting of the harness.

The easiest method is to measure from the base of the lumbar plate, between the legs and up to the top of the waist buckle. If you don’t have a tape measure, just use some string and knot it at the correct distance.

Now you can fit the length of your crotch strap accurately, without having to fumble between your legs. Measure out the correct distance and thread this through the outside of the lower slot on the lumbar plate. Then secure the surplus webbing back through the rear crotch strap D-ring tri-glide.

The crotch strap should be adjusted to fit very snug, but it shouldn’t be painful.

measure the crotch strap andy davis subic philippines

Bear in mind that when diving you’ll be in (I hope!) a proper “trim position” and the resulting slight arch in your spine will reduce the distance between the shoulder and lumbar plates. This will relax the fit of your sidemount harness… especially the crotch strap. What seems tight when standing, should feel comfortable when diving.

Once you’re happy with the length of the crotch strap, you can trim off the excess webbing material.

Most soft crotch straps come with an excessive length of webbing. Leave maybe 6″ to be sure. Thread the remainder through some rubber loops that you’ve put on the crotch strap.

Lastly, you need to properly locate the rear crotch D-ring. That should sit just above the crease of your buttocks, NOT between your buttock cheeks. It’s a common error and an uncomfortable one.

diving equipment setup copyright 2019 Andy Davis

The rear crotch D-ring is where you’ll stow items like reels, spools and DSMBs. You want to avoid these lumpy objects falling between your legs when diving.

Sidemount harness bungee system

Step 9a – Fitting the Loop Bungees

If you’re using loop bungees (recommended for most people), then now is the time to fit them. Thread one end of the bungee through the top of your rear tri-glide, bring it forwards under the armpit and thread it down through whatever you’re using as a front retainer (tri-glides or rubber o-rings). Then route it back under the armpit and back through the tri-glide at the rear. Secure it using simple overhand knots at each end.

Click here for full instructions on how to setup Sidemount Loop Bungees.

Harness Set Up copyright 2019 Andy Davis

Test your bungee length by inserting your thumbs through one strand of the bungee on each side. Bring the bungees together at the front of your chest.

As a rule of thumb, the correct length for loop bungees is when you can stretch them comfortably to the nipples; and at full stretch (high tension) they should meet together at the sternum.

Once sized appropriately cut off the surplus bungee. Leave maybe 4-6″ extra initially; pending in-water testing and adjustment.

Step 9b – Fitting Continuous or Independent Bungees

If using a continuous bungee system, it runs through the spine strap at the rear – the gap between the main strap and the surplus that you folded back down and secured through the tri-glide. If you like a little more security on a continuous bungee, you can run it through the holes in the lumbar plate.

With independent bungees, you can run each length from holes in the shoulder plates at the rear.

For either method, the bungee runs under the armpit and up to the front D-rings. Most divers connect it to the D-rings via medium sized boltsnaps.

The drawback to that is more clutter on the D-rings; which is especially poignant to technical divers who’ll be adding lots more boltsnaps to those D-rings when they attach multiple deco/stage tanks.

The alternative, which keeps the D-rings less cluttered, is to thread the bungee through/under the webbing where it runs through the D-ring tri-glide. Just thread the bungee between the webbing and the tri-glide; then tie an overhand knot on the other side.

With continuous or independent bungees, the proper sizing is to run it snug up underneath the armpit. It shouldn’t dangle down below the armpit, but neither should it be painfully tight. Once sized correctly, tie knots in the bungee to secure it in the tri-glide and cut off the surplus. Leave maybe 4-6″ extra initially; pending in-water testing and adjustment.

I hope that helps some people. If you’re having problems with your own sidemount harness configuration, please do drop me a line – I’m happy to help. Video or photos do help with a diagnosis.