HOW TO: SET UP A TWINSET - PART 3: HARNESS AND BACK PLATE

This article is designed to allow the reader to set up their twin cylinders based on a Hogarthian/DIR setup.  The information below is based on how I dive and how my equipment is configured (unless teaching where agency standards dictate otherwise), however other methods are available.

Overview

On my previous blogs I’ve shown you how to choose and setup twin cylinders (here) and wings (here), as well as discussing what a Hogarthian setup and DIR is.  Moving forward we’ll look at choosing a back plate and setting up a harness.

Happy reading.

The harness and back plate

It’s amazing that despite all the latest fads, one aspect of diving that appears to have gone full circle is the buoyancy device.

I’ve been diving a wing, back plate and harness on my twinset since 2007 however as I mentioned at the start of my cylinders blog it wasn’t always in this configuration.  I also used to dive a buoyancy compensator device (BCD) for recreational diving but saw the light and switched to the Hogarthian setup in 2011 for all of my diving.  I think that a wing, back plate (BP) and one-piece harness (OPH) gives a more stable body position in the water, but most importantly no matter what equipment configuration I’m diving (OC single, OC twins or CCR) I can bolt on the same back plate and harness, choose the appropriate size wing and off I dive safely in the knowledge that all the dumps, clips and D-rings etc… are in exactly the same position, so if I’m doing a drill, or more importantly in an emergency, everything is muscle memory.  Although BCDs are far more common, my personal belief is that more and more people will convert to this setup; look around at most dive sites and I think you will agree.  By following this guide you can purchase one piece of equipment that will stay with you as your diving progresses, and if it breaks you only need to replace that individual item rather than the whole setup.

Harness

There are generally the 3 types of harnesses (technically 4 if you include a BCD), the one-piece harness (whether home made or purchased), harness with a break (with a similar setup to the OPH) or a commercially purchased harness.  I have deliberately ignored the BCD as a. I don’t agree with them and b. the cylinders are generally positioned too far away from the diver to enable them to reach the valves.  Each style is described below:

1.  One-piece harness.  A one-piece harness is exactly what is says; one piece of webbing weaved through the back plate without any quick-release buckles or other failure points.  By having a near infinite amount of adjustment on the hardware (D-rings, buckles) the harness can be setup to get the perfect fit and adjusted based on exposure suits.

2.  Harness with a break.  Some divers have a harness setup in a similar way to a one-piece but like the flexibility a quick-release clip adds when kitting up or de-kitting.  These clips may appear to simplify the process but in fact can add complications in an emergency.  Some instructors state that if a quick release clip fails the diver will lose their twinset.  This is not the case.  In fact, many divers with a break deliberately dive unclipped when this is pointed out to them just to prove a point.  The reason a buckle (probably) won’t fail is because if, or in some cases when a diver is neutrally buoyant there is no tension on the buckle.  If it were to fail the diver could carry on the dive.  The issues the diver would face would arise when he needs to reach his valves as the cylinders would move around on their back.  Also when carrying stage cylinders the cylinder would either hang dangerously low in the water (if the D-ring was below the break) or swing around in the water (if the D-ring was above the break).  Regardless of which, it would off-balance the diver in the water.  The only time a quick-release tends to fail is when kitting up and it’s not secured properly and goes ‘pop’ when the diver stands up.  Also there is the risk of the buckle breaking if it’s made of plastic, especially if stood on or squashed on a dive boat.

For the apparent flexibility the diver wrongly believes a break brings, they put themselves at a greater risk in an emergency situation.

There is another break that I will mention and that is a continuous break.  This is basically a harness configured as per a one-piece harness but with a loop normally on the left shoulder.  The loop is normally secured shut with a buckle.  Divers use this is they want an easy way to de-kit with the belief that they retain the benefits of a one-piece as there is no physical break.  However the same disadvantages regarding the diver being off balance still apply if the buckle fails.

3.  Commercially purchased harness.  Commercially purchased harnesses, like a BCD are only manufactured in a limited number of sizes.  Because of this they are not fully adjustable so have a number of D-rings positioned over the harness, a quick-release clip on either one or both shoulders and potentially a chest strap.  This make the chest area very cluttered and usually results in the diver fumbling around to identify which D-ring they have used, and make the stowage of a backup light in the traditional way near impossible.  Also, as the design is not one piece there tends to be a number of stitching points that could potentially fail.  And finally if an item on the harness does fail you cannot replace the individual item so a complete system must be bought.

The commercially purchased harness in the picture has had a lot of the unnecessary accessories removed to make it as simple as possible.  On first impressions this may look ok (break aside) however on further inspection it is constructed from 4 separate pieces of webbing which are either sewn together via a ring or weaved together through a tri-glide.  These are potential failure points.  Originally it came with a 1”/25mm crotch strap and break with no rear D-ring for stowage which I would not recommend.

One piece v modified commercial harness

Hopefully by now you can see why I, amongst others favour the simple one-piece harness.  Is there anything else?  Some divers may argue that 3 D-rings is not enough, however there are numerous divers who dive with multiple stage cylinders, DPVs and/or cameras who seem to cope really well.  I tend to look at it in the same way as packing for a holiday; the larger bag you have the more you are tempted to fit in it.

There are divers that like the principle of a one-piece harness but like the flexibility of adjustment, so choose a system like the Halcyon's Cinch, Agir Brokk's Harpa or Kent Tooling's Winch.  These are all excellent systems that really work well in their own right however I’ve never felt the need for one as with the correct technique a one-piece harness is easy to remove.  This is a technique that is easier to demonstrate rather than explain so I will not attempt to, however please feel free to ask if you have any questions about this.  Lastly an adjustable harness due to its nature may not be sized exactly the same every dive.  In an emergency where the diver is unable to de-kit themselves the harness can be cut off as each diver carries a knife or cutting device on the waist strap.

Crotch strap

Although considered part of the harness, I know a lot of divers who do not dive with a crotch strap however I believe it is invaluable and use one for all of my diving, including recreational dives.  The crotch strap itself has 3 functions:

1.  Preventing the set from riding up, especially whilst at the surface.

2.  For use with a DPV.  The front D-ring (often known as a scooter ring) is used as a DPV attachment point.  In the event of a DPV failure the DPV can be clipped to the divers rear D-ring whilst the said diver is towed by his teammate’s/buddies rear D-ring.

3.  Equipment stowage.  Additional equipment such as stage cylinders, primary reels, jump/gap reels etc... can be stored on the rear D-ring.  Equipment should never be clipped onto the front D-ring as it will hang below the diver, which causes drag, but can cause environmental issues as the equipment can knock against the reef, cave floor etc… especially in restricted areas. 

Back plate

As a general rule of thumb a back plate is a back plate.  Most are generally a standard size however some are slightly wider than others and some manufacturers offer a short version; some only come with a 1”/25mm crotch strap slot, some with a 2”/5cm slot and some with both; and others have cam band slots if you wish to use it without a single tank adaptor (STA) when single cylinder diving.  If you intend mixing and matching brands it is important to ensure they are compatible. 

Then what material, aluminium or stainless steel?  Generally in the UK most divers opt for a stainless steel back plate due to the weight. 

Construction of a harness and back plate

Purpose made harnesses are available from companies such as Halcyon or DIR Zone, or you can make your own.  If you choose to do the latter you will need the following:

1.  Approx 4m of 2”/5cm webbing.
2.  1x stainless steel buckle.

3.  4/6x 1cm mountain bike inner tube strips.

4.  2x D-rings.

5.  2x bent D-rings.

6.  6x tri-glides.

7.  1x Crotch strap with integrated D-ring.

Note:

1.  If you choose to have a fixed D-ring on the left hip as I do you can remove one D-ring and one tri-glide from the list.

2.  You can make your own crotch strap if you so wish.  For this you will require at least 1m of 2”/5cm webbing and an additional D-ring and tri-glide.

In addition you will require the following items to complete the setup:

1.  1x Knife or cutter with a 2”/5cm webbing attachment.

2.  1x stainless steel buckle.

3.  1x Back plate.

4.  1x LPI O-ring or length of 3mm bungee.

And you may require the following tools:

1.  Lighter.

2.  Knife/scissors.

3.  Soldering iron (if webbing does not have a fixed eyelet).

4.  Spare mushroom bolt (not essential).

Firstly find the center of the webbing.  If it is a purchased kit there should be an eyelet, if not you will need to make a hole.  You can do this with either a knife and a lighter or a soldering iron to melt though the webbing.  Whichever method you use you should ensure that the webbing is melted all around the hole so it does not fray.  Alternatively if you have access you could use an eyelet kit.  The hole needs to be large enough to accommodate a bolt from the twinning bands off your twinset cylinders.

Once this is done, I find the remainder of the setup is easier if the eyelet is secured to the hole on the back plate to prevent movement.  I do this with a mushroom bolt however any size bolt could be used, or even a cable tie.  The webbing should be on the outside (cylinder side) of the back plate.

Thread the webbing through the angled slots to the diver's side of the back plate and then back through the upper slots.

On the webbing on the divers right side, thread the webbing through one tri-glide, over a bent D-ring and down through the tri-glide.  The bent D-ring should be bent away from the harness as shown in the picture.  This makes clipping off much easier.  The final position of the D-ring should be approximately 12 inches from the top of the back plate but this will be fine tuned later.

Repeat the process on the webbing on the divers left side.  

The only difference is that you will need to capture the O-ring or bungee in between the tri-glide and D-ring.  If you’re not aware, the O-ring or bungee is used to retain the LPI attached to the wing so should be sized accordingly.  The 2 ends can be secured by a reef knot with the ends melted to prevent fraying.

Next slide 2/3 lengths of inner tube up each length of webbing.  These are used to secure backup lights to the harness.  Lights will be discussed in detail on a separate blog.  One length of inner tube should be approximately 6-8 inches below the D-ring to secure the light, although the length of the light will dictate the exact position of the inner tube.  The remaining lengths should be positioned just below the D-ring as spares. 

On one side (either is fine) thread the webbing through the inner angled slot at the bottom of the back plate, then through a tri-glide, then out of the outer angled slot.  The tri-glides are used to stop the webbing slipping through the back plate and adjusting the harness once correctly sized (which we will do later).  You will know if you’ve done this correctly as the outer facing webbing over the shoulders becomes the inner facing webbing around the waist.

Add the left hip D-ring and tri-glide to the divers left waist strap.  This wants to be aligned with the center of your body but for now a hand’s width from the back plate is fine (it will be re-positioned later when the harness is correctly sized).

Next we add our knife or cutting device onto the divers left waist strap.  It should be positioned so that either hand can access it in an emergency.  Some people choose to add a second knife or a cutter for redundancy which, although not essential can be done.  My second cutting device is added to my primary light here.

The final thing to go on the divers left waist strap is the stainless steel buckle.  From the front thread the waist strap through the large end slot of the buckle, back through to the front then through the inner slot to the back.  The final position of the buckle wants to be on the divers right side so it does not interfere with the crotch strap (as before will be re-positioned later when the harness is correctly sized).  Once happy with the position thread the webbing through the back of the large end slot so there are two thicknesses of webbing through the same slot with the excess webbing doubled back and laying flat along the inside of the divers left waist strap.  Do not cut off any of the spare end until the harness is correctly sized.

Lastly we add the crotch strap.  The crotch strap consists of a pre-woven loop, a D-ring (or scooter ring) at the front, and a D-ring complete with tri-glide at the rear.  The rear D-ring and tri-glide should be threaded onto the crotch strap, the strap passed through the back plate rear to front, and then back through the tri-glide.  Any excess webbing should lie flat along the inside crotch strap.  The exact sizing and D-ring placement will be covered later.

If not already done so the mushroom bolt can now be removed.

Setting up a harness and back plate

The following is only a guide and should not be used verbatim.  All adjustments should be done whilst wearing the relevant exposure suit, whether it’s a dry suit with under suit or a wetsuit.  Final tweaks may still need to be done after a test dive and vary from diver to diver.

Regarding the harness, it should not be too tight or too loose.  One of the common mistakes I see people make with an adjustable harness, similar to a traditional BCD, is that the straps are too tight.  When a harness is too tight this can restrict shoulder movement making reaching your valves much harder.  Also, without a break it makes removing the harness much more difficult.  In contrast, the harness needs to be loose enough to allow it to be removed, but if the harness is too loose the cylinders will move around on the divers back and the harness will hang low whilst the diver is wearing stage cylinders.

Without the waist or crotch strap fastened, adjust the shoulder straps.  With the top of the back plate an inch or so below the prominent vertebra at the base of your next you should be able to touch the top of the back plate.  As a rule of thumb, unless you’ve suffered a shoulder injury everyone should be able to do this.  If you cannot it’s probably more down to technique rather than flexibility.  I could write another article on this and why it’s done in a certain way however it’s best demonstrated.  For the purposes of this article, place your head back, look up (as if you were in the horizontal position in the water), reach forward with your arm and then straight back (rather than from the side).  If you look at the 2 pictures you can see what a difference the correct technique makes.

Next we need to check that we can fit a fist through the shoulder straps.  This will ensure it’s loose enough to remove in the water.  As previously explained this is a technique that is easier to demonstrate rather than explain.

The above 2 points may take some fine-tuning so repeat as necessary.

Next we look at the position of the shoulder D-rings.  This is very important as this is where most of your equipment gets clipped off (backup lights, stage bottles, primary regulator and primary light – both when not in use, cave arrows/cookies, camera etc…).  The D-rings should be positioned where you instinctively reach for (muscle memory) whilst continuing to look forward, either at your buddy/team mate or whilst finning.  You should not have to look at your D-rings to clip anything off; if you do they are in the wrong position.  Additional issues with the D-rings positioned too low is that they will cause stage cylinders to hang too low resulting in the same issues I mentioned when talking about the crotch strap.  Other implications of the D-rings positioned too low is that they may not be enough room to fit a backup light, and, on the divers left side where the O-ring or bungee is positioned, enough room to raise the LPI to dump gas from the wing in an emergency.

As a rule of thumb the D-rings should be positioned in line with the armpit.  We can then fine-tune this by holding our arms out parallel with the ground and then bring them back in.  Our thumbs should be in line with the D-rings.  We can then fine-tune this further with the aid of a p-clip.  With our eyes closed, p-clip in hand we repeat the process but instead trying to clip the p-clip to the D-ring in an upwards direction.  P-clips should be clipped on in this manner as the natural bend makes it easier to locate and we lift the D-ring away from the harness.  By clipping off in a downward direction all we do is push the D-ring into harness making it harder to locate.

Once we are happy with the sizing and the positioning of both D-rings we need to check that both the left and right sides are the same.  The easiest way to confirm this is to stand on the crotch strap and lift the harness up by the shoulder straps.  Make any adjustments required to ensure they’re both the same but ensure so you double check the harness sizing and D-ring locations as listed above.  Again this may take some fine-tuning so repeat as necessary.

As mentioned during the construction the waist D-ring wants to be aligned with the center of your body.  You may require the assistance of a buddy or a mirror for this.  If the D-ring is too fat back it may interfere with your suit inflation cylinder (if fitted) and if too far forward any stage cylinders will hang too low resulting in the same implications as before.  Further in-water adjustments may need to be made once you have practiced clipping off your SPG and/or stage cylinders however like the shoulder D-rings it should be in a natural location.

No further adjustments are required to the knife or cutting device so we move onto the stainless steel buckle.  The waist strap should come straight around the divers front and not sag however for those that are a little ‘larger’ around the waist it may have to be loosened off slightly.  The waist strap should be tight, but not too tight as to restrict breathing and as mentioned during the construction the final position of the buckle wants to be on the divers right side so it does not interfere with the crotch strap.  The reason for this is to prevent the crotch strap from accidently opening the buckle on the divers waist.  Once fastened, any spare end can be tucked behind the knife or cutting device.

The last area of adjustment is the crotch strap. On a purchased crotch strap there is little adjustment on the front D-ring.  With the waist strap fastened, the length of the strap should be adjusted so that the strap passes through the divers legs with the loop finishing approximately 1”/25mm above the waist strap.  If too long it will hang beneath the diver and if too short it will pull the back plate down which will in turn make it harder to reach the cylinder valves.  



Next we need to position the rear D-ring.  It should be approximately 1 hands width below the back plate and it should be able to be reached with a single hand.  If positioned too high it will be hard to clip off and if to low the equipment will dangle.  Once completed, as a final check, with the waist and crotch strap fastened you should still be able to touch the top of the back plate.

Once the harness is correctly sized you can cut off any excess.  Any spare on the divers left waist strap or crotch strap can be secured by an additional loop of inner tube.

Lastly, if using a canister/primary light with a separate battery pack we add a second stainless steel buckle on the divers right waist strap to keep it in place.  One could use the stainless steel buckle on the harness however if the harness is removed in-water the additional buckle will prevent the canister/battery pack from sliding off the harness.

Finally

Is there anything else that still hasn’t been covered?  Equipment stowage?  Other than backup and primary lights, and distance reels, you will notice from this blog I’ve not mentioned the stowage of basic dive equipment such as DSMB, spare mask etc…   Unlike a traditional BCD there are no pockets to store such items so you could buy a waist pocket, however I prefer to store them all in my drysuit pockets as it prevents looking like a Christmas tree and aids streamlining.  This is a separate article that I intend to write, however for the time being the equipment that I intend to use on a dive is in my left pocket with the emergency equipment in the right.  The reason for this is because stage cylinders are carried on the left therefore the access to the right pocket is un-restricted if I were to need the equipment in a hurry.  More information on what I carry and where can be found here.  The only other equipment we may carry is a lift bag.  Some people prefer to store it in a storage pack on the back plate (link) however I prefer to use 2 lengths of bungee cord at the base of the back plate.  The important thing to remember with this method is to ensure the crotch strap passes on the INSIDE of the lift bag. 

What about changing exposure suits?  Due to the flexibility on a one-piece harness it is possible to adjust it depending on the exposure suit; a UK drysuit with thick undersuit will require a different fitting to a 3mm shortie in the Maldives for example.  Although most divers tend to have a (stainless steel) back plate and harness for the UK, and a (aluminium) back plate and harness for holidays.

I think that covers it.  Hopefully by now you understand the reasoning behind a one-piece harness and know how to construct and set it up correctly.  Your twinset should now start to resemble something like the picture.

I hope you enjoyed this article and if you have any questions please ask.  I would however always recommend speaking to an instructor about your own individual equipment requirements.

The boring bit!

All opinions expressed in my articles are my own and may differ to other instructor’s and agency guidelines; by no means are they wrong and I would not wish to disrepute any of them.  This article is for information only and should not replace proper training.

Safe diving!

Timothy Gort

BSAC, PADI & SDI/TDI diver training
l Mob: 07968148261 l Email: tim@rectotec.co.uk l