How to Size a Backplate
by David Chamberlin
Photos by Sami Laine and Clinton Bauder
The backplate and wings setup is one of the defining pieces of DIR equipment.
This configuration embodies many of the properties that DIR divers demand from their
equipment. It is streamlined, durable, easily maintained, adaptable, minimalist,
robust, and highly configurable, to name a few. Ironically, one of its greatest
features - its ability to be configured for any body size and shape - leads to
problems for many new DIR divers. The harness setup truly deserves the
one-size-fits-all moniker. Unfortunately most dive store employees are not well
versed in the proper sizing and configuring of a backplate harness. The result is
that divers are left with ill-fitting equipment that can cause discomfort or even
pose dangers to the diver.
By far the most effective way to ensure a proper fit is to have a knowledgeable
professional provide direct, personal assistance. With the success and proliferation
of the GUE DIR Fundamentals class, this option is becoming more accessible to a large
number of divers. The GUE instructors work through proper sizing and configuration
of equipment with each student individually, assuring a proper setup, as well as
helping the students understand the process. If you are not able to attend a DIR
Fundamentals class, or would like to get a head start, the following are some
pointers on achieving a proper fit and correct configuration for your harness setup.
It is very important to perform all of the sizing and positioning while wearing
the full exposure suit: full undergarments and drysuit, full wetsuit, etc. A
thick exposure suit can have a dramatic impact on the sizing of the harness.
The best place to start is with the arm straps. Here we are trying to balance
The arm straps need to be loose enough that the harness is
comfortable and that the rig can be easily doffed/donned both in-water and
out-of-water. The straps also need to be tight enough so that the tanks do not
slide around the back and stage bottles clipped off to the chest d-ring stay close
to the chest.
Start by loosening the arm straps to the point where there is a lot of slack and put
the harness on.
Position the plate in approximately the correct position on the back.
As a starting point, place the top of the plate a little below the first pronounced
vertebrae at the base of the neck.
With the plate in this position, you should be able
to touch the top of the plate (Figure 1).
If you can accomplish this, your chances of reaching your valves when your rig is fully
assembled are good.
With the plate in that position, tighten up the arm straps somewhat
snug. The straps should not be tight - you should be able to get at least 2 or three
fingers underneath the strap (Figure 2).
You want it loose enough so that you can slide the straps off the shoulders
(Figure 3). This should also enable
you to pull the rig over your head when doffing/donning in the water. Again, you
need to avoid making it too loose.
With excessive slack in the arm straps, the plate
will ride low on your back, making it nearly impossible to reach your valves.
In addition, the shoulder straps will hang loose on your body when in the horizontal
position, which will be exacerbated by stage bottles clipped to the chest d-ring,
causing the stage bottles to hang in the slip stream, inducing increased drag.
Once the shoulder straps are correct, next work on the waist strap. The waist
strap adds much of the stability in the harness configuration.
Whereas the arm
straps are somewhat loose to add comfort and mobility, the waist strap is fairly
snug to keep the rig in place.
As much as possible you want the waist strap to just come straight around and not
"sag" too much (Figure 4).
However you don't want it to restrict
breathing from your diaphragm, so if it is restricting breathing or you have a
somewhat pronounced belly, you may need to let it go down just a bit. The waist
strap should be snug, but not so snug it restricts movement or breathing. When
adjusting the waist strap, make sure to set the buckle so that it is off to your
right side. With the buckle in this position, the crotch strap is unable to
accidentally open the buckle. The waist strap buckle can also be used to hold
the light canister in place. However if the rig needs to be removed in-water, it
is suggested that an additional buckle be slid (not threaded!) on the strap to hold
the light canister. This will prevent the canister from sliding off the waist
strap when the waist strap buckle is released.
The final piece of the harness that needs to be sized is the crotch strap.
The crotch strap's two primary functions are: keep the rig from riding up
(primarily at the surface), and for use with a tow-behind scooter.
If a failure
occurs while scootering wherein a diver needs to be towed, the towed diver holds on
to the crotch strap of the towing diver. Therefore the crotch strap needs to be
loose enough that a diver can comfortably grab on to it, yet it also needs to be
snug enough so that the rig does not ride up.
Start by buckling the waist strap as you normally would, but do not run it through
the crotch strap. Now pull the crotch strap up to the waist band. Set the length so
that the top of the crotch strap reaches the top of the waist strap
If you want to give it even an extra 1/2 inch or so, that should be fine.
Many people make this too short, which then pulls the plate down and restricts the
ability to reach the valves.
As a final check of the sizing, with the plate on, the crotch strap on,
waist strap tightened, you should be able to reach back and touch the top of
the plate (Figure 1). If you can
accomplish this, then likely the sizing
is reasonably close. The true test will be in the water. Don't be afraid to
readjust the lengths based on in-water experience.
Once you have the sizing about right, you will want to get the d-rings into the
proper position. Incorrectly positioned d-rings can cause a variety of problems,
from inability to effectively clip/unclip gear, to increased drag caused by stage
bottles, and even inability to dump gas from the BC inflator hose. The harness
should have at most 5 d-rings: 2 shoulder d-rings, one d-ring on the left hip,
one d-ring on the rear of the crotch strap, one d-ring on the front of the crotch
The shoulder d-rings are where most of the gear is clipped off. These d-rings
should be positioned relatively high on the arm straps for a variety of reasons.
One of the primary reasons is that stage bottles need to be held close to the chest.
If the d-rings are too low the stage bottles will hang away from the diver out of the
slipstream causing drag, banging the reef, etc. D-rings that are too low will also
cause problems with positioning of the backup lights, especially on shorter-torso
people, as there will not be enough length to fit the light snugly. An
often-overlooked aspect is the ability to dump gas from the wing. Since
the bungee cord that holds down the inflator hose runs under the triglide for
the d-ring, if the left side d-ring is too low, it will restrict the diver's
ability to raise the inflator hose to dump gas.
To position the shoulder d-rings, extend your arms straight out to the side,
parallel to the ground. Bend at the elbow and bring your thumb straight to the
Where you hit the strap is a reasonably good starting point for
placing them (Figure 6). It will likely
be almost inline with your clavicle,
possibly a shade lower. First check to see how easy it is to clip/unclip gear
there and how natural that position feels. Next, with your right arm, reach across
your body to (or almost to) your left shoulder. Make sure the d-ring doesn't pinch
between your arm and chest (Figure 7).
Do the same with your left. If it
pinches, it is too low and needs to be moved up. These d-rings generally should
be as high as is comfortable/reasonable to clip off one-handed on the same side
(i.e., one-handed clip off of gear on right d-ring with right hand
You should not rely on reaching
across with your opposite arm to clip gear off, as that arm may be occupied doing
The waist d-ring is used for clipping off the SPG and for stage bottles.
A common mistake with the waist d-ring is to move it too far back
(towards the plate). Several problems are introduced by having a waist d-ring too
far back. It becomes much more difficult to clip/unclip gear, especially if the
diver is using a "wreck mounted" argon bottle. In addition, since most of the
bottles used as stage/decompression bottles are slightly buoyant, if the d-ring
is too far back the tail of the bottle will ride high enough o be out of the
slipstream. Of course, having the d-ring too far forward introduces another
set of problems.
Stage bottles and the SPG will hang too far forward, out of
the slipstream, causing drag and increasing entanglement hazards.
To position the waist d-ring, run your left thumb straight down your left side
until it hits the waist strap. This should be a good starting point. It should be
right about where you can feel your hip bone (Figure 9).
This one may need
further adjustments based on in-water testing. Practice clipping/unclipping the
SPG and if you wear stage bottles, have your buddy check the position of the tanks.
The rear crotch d-ring is generally used for storing gear that is not used
very often, such as reels or lift bags. This d-ring needs to be low enough that
ou can clip/unclip gear there (and not be blocked by the bottom of the tanks), yet
high enough that the gear does not hang down too far. The rear crotch d-ring is
considered an optional d-ring. If you have no gear that needs to be clipped in
this position, it can be removed.
To position the rear crotch d-ring, you generally want it about one hand-width
down from the bottom of the plate (Figure 10).
If it is too much lower than
that it will be more difficult to reach, and the gear will likely be hanging too
low between the legs, interfering with fin kicks. If it is too much higher the
bottom of the tanks will often block access, and those with drysuits may find
flexibility is reduced enough that reaching the d-ring will be very difficult.
The front crotch d-ring is only used with a tow-behind scooter. Gear should never
be clipped to this d-ring, as it will hang in the slipstream and pose significant
entanglement hazards. This d-ring is often sewn in, so there is generally little
choice in placement.
A properly configured backplate harness is an amazing piece of gear that can
greatly increase a diver's comfort and safety in the water. By following these
directions, one should be able to come relatively close to achieving this. However
the ultimate test is how it performs in the water. Find a good buddy, go for dive
and have fun!