Backplates

The "backplate" actually consists of four stainless steel plates. Two threaded backing plates go inside the unit. The small plate in the bottom of this image is the top backplate that holds the top of the harness. The wide plate attached to the bailout bottle rack is the bottom backplate. The contour of the part of the chassis that goes against the divers back is critical to keeping the counterlung as close as possible to the divers lungs to keep breathing resistance to a minimum. If the counterlung is spaced away from the divers back, the breathing resistance goes up. This system keeps the rig nice and close to the divers back.

Image courtesy of Enrique Avalerez.

Bailout Bottle Rack

The original Mk15 did not have any accommodation for carrying bailout gas in the event that the entire unit floods. This rack allows for the attachment of an additional gas cylinder to the bottom of the unit that the diver can switch to in the event of a system failure. One thing that is very important to consider when designing a bailout bottle rack for the Mk15 is the weight. The unit is already heavy in the butt and any additional weight makes it worse. This rack is very lightweight being made out of titanium. The tab at the top slides between the bottom backplate and shares the same mounting hardware. It has the additional benefit of allowing the unit to stand on its own making it easy to dress into.

Image courtesy of Enrique Avalerez.

Backing Plates

This image shows both the bottom and top backing plates installed into the chassis.

Top Backing Plate

The top backing plate is shown here installed in the unit. The bolts pass through two of the existing water pass-through holes already in the unit. Acorn nuts are welded into this plate to keep the ends of the screws from damaging the counterlung. All of the edges have been carefully rounded.

Holes

The water pass-through holes in the chassis are much larger than the screws that have to pass through them. I used these washers to keep the backplate centered up during installation and to reinforce the holes. They are slightly thinner than the fiberglass so they sit down in the holes slightly.

Upper Backing Plate

Here you can see the upper backing plate installed in the chassis. A small dab of adhesive keeps it from falling out if the backplate is removed. Another small dab of adhesive keeps the two washers in place. The entire unit has to be stripped to install these plates so you don't want to have it drop free if you remove the wings. Getting everything to line up the first time this plate is installed before the adhesive sets was quite a challenge and a task I would rather not repeat.

Bottom Backing Plate

The location of the bottom backing plate is critical. Two holes have to be drilled in the chassis to allow the screws to pass through. I have to admit I was a little nervous taking a drill to my Mk15. It was definitely a measure twice and cut once operation. This plate is also secured in place with a little bit of adhesive.

Location

With the rest of the components installed in the chassis, you can see why proper location is critical. The electronics pod sits just off the plate. The connectors just miss the two screws that hold everything in place (not shown).

Bottom Backplate

Here you can see the bottom backplate attached to the chassis. Two screws pass through this plate, the chassis and screw into the backing plate on the inside of the rig. The Bailout bottle rack is sandwiched in between this plate and the chassis when installed and shares the same hardware.

Backplates Installed

This image shows both of the backplates installed without the wings or bailout bottle rack. The next task was to get out some 2" webbing and make up a harness.

Harness

For the harness I ran two pieces of 2" webbing. The top of the harness is looped through the stainless steel loops in the upper backplate. Two stainless steel weight keepers were used to make the loops. I used two additional weight keepers to attach two stainless steel D rings to the shoulder straps. The shoulder straps loop around, feed through the welded loops in the bottom backplate and become the waist strap. The lower backplate already has D rings attached so I didn't need to add additional ones here. I added a 2" Fastex clip to finish off the waist strap.

Bailout Bottle Rack

Here you can see a close-up of the titanium bailout bottle rack mounted to the rig. It uses a wide band to wrap around the bottle. A hose clamp is attached to the strap to allow the bottle to be tightened securely. A nice wide handle allows one to remove the bottle without tools.

Bottom Harness

The webbing for the harness covers up the heads of the screws holding the whole thing together. The small loop in the center of the image is where the crotch strap will be attached.

Bailout Bottle

I put my 13 cu.ft. pony bottle in the rack to test it out. The rack holds it securely in place.

Wings

The next project was to modify an old pair of Dive Rite classic wings to bolt up to the rig. The silver grommet to the top is the existing one that is used with a set of doubles. The first step was to measure and punch two holes for additional grommets. This is the bottom of the wings.

Grommet Installation

After punching the holes, I installed two grommets and pounded them into place. I used 3/8" brass grommets for this project. This is the top of the set of wings. I placed the grommets as high on the wings as I could without going into the bladder.

Wings

Here is the set of wings with all of the grommets needed to hold it in place. I left a little extra slack between the top and bottom set of grommets so the wings could follow the contour of the chassis.

System

In this image you can see the whole harness/backplate/bailout bottle rack assembled. I got out a little patriotic 1" webbing and made up a crotch strap to complete the harness.

Scooter Ring

In order to attach the crotch strap to the waist strap I had to make up this webbing loop. I copied the loop from my Dive Rite harness and incorporated a scooter ring. I used a 1" Fastex clip to attach this loop to the crotch strap. I put on my Martha Stewart cap, got out some heavy-duty carpet thread and a big needle and went to town. Sewing the webbing was not easy but should do a nice job.

Crotch Strap

A simple 1" webbing keeper was used to make a loop to attach the crotch strap to the lower backplate.

Together

With the sewing done, here is the whole harness together. It does a nice job of holding the rig securely in close to the divers back.