I've started a project and am not sure of the chances of success, but if you like DIY stuff it may be fun to follow along- I love following build threads like this, and I always welcome the pointers and tips of a group.

My current solo carry yoke is solid ash, with DIY yoke pads and modified spring creek clamps. It is robust and works really well and I love it. ...but, it's heavy. 4lbs, 6oz heavy. Ive been thinking for a long time that this may be an opportunity to cut POUNDS from my portage load. It's also an opportunity to experiment with some new materials/construction techniques and maybe learn something/ maybe destroy something.



Design goals:
-Retain the same (right/left) pad spacing and clamp spacing of my ash yoke.
-incorporate some sort of rise/lift for better visibility when portaging.
-try to center the clamps (front/back) over the center of the shoulder pads (front/back). with the current straight ash yoke I feel like the back of the yoke is right against the back of my neck, forcing my shoulders to be under the very front edge of the pads and putting a twist/torque on the clamps where they grab the gunwales.
-utilize carbon fiber composite in a structural manner to keep things light, strong, and stiff. Ive used carbon and fiberglass in hand layups and cosmetic parts before, but I really want to experiment with vacuum bagging and infusion to make lightweight, structural parts with high fiber/resin ratio. This is really what this project is about: I care less if I actually end up with a better yoke, but more about the learning and the process itself.

I start by modeling the existing yoke in Sketchup (above) and go from there. I think I have my final design now ready to start building. It has a 3" lift and sweeps the clamps 2.5" forward of the old 'straight' yoke position.



note: I had difficulty modeling the pad/yoke connections in sketchup and while I do have a plan for it, the drawings above just show them floating in space.

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The exact engineering of how robust this has to be is also beyond my knowledge. I can calculate the force of a 40b canoe(overloaded) accelerating down on your shoulders should you step down an 18-inch rock, but that is almost useless because I then don't know how much carbon fiber is needed to resist that force, or in what construction/ orientation.

So I will estimate things and maybe test/destroy some parts along the way, but probably err on the side of over-engineering this at the expense of some added weight. But hey, as long as it's less than 4lbs, 6oz I'll call it a win :)

The major stress on the yoke will be vertical bending in the frontal plane of the 'U' that makes up the main beam. The U shape helps to resist this, but stresses will be concentrated toward the corners, where the U transitions into a flat surface for the clamps. The beam will be hollow/foamcore with the majority of the stress carried in the "skin". To improve stiffness in the vertical direction, I could definitely make it thicker than the 3/4" shown in the drawings, but my initial plan is to instead construct the beam by laminating strips of 3/8" PVC foam together in a vertical orientation with layers of CF in between to act as internal stringers. This will behave more like a box-beam and make it very stiff in the vertical direction, while the layers of foam/carbon will act like a sandwich-core in the front-back direction.


I'm also hoping the box-beam helps to resist the twist/torque induced in the beam by sweeping the clamping points forward. (twist force that was previously in the clamp where it grabbed the gunwale is now moved to the yoke beam itself) The inspiration for this came from looking at bridge construction: Curved bridges resist similar twisting loads, and they often use box-beams to do this.

Sounds like a great project, looking forward to following along!

I was able to 'flatten' surfaces of the model and print full size drawings.
I used this to cut sections of 3/8" PVC foam for lamination. These are oversized, as they will be cut down later. I registered the position of each by skewering them together with cocktail toothpicks.




Next, I cut plys of 6oz carbon fiber to laminate between the foam sections. Taping the edges creates a little waste on each piece, but prevents unraveling of the cloth while working and laminating it. I cut these pieces on a bias, so the fibers will be aligned diagonally to the length of the yoke (like diagonal members of a truss).



I printed a top view of the yoke and made a mold from XPS building foam covered in packing tape. I will vacuum the laminate against this mold to create the 2.5" forward/backward curve.




Once everything was ready I mixed resin and laminated each carbon ply into the foam stack, using the toothpicks to keep the stack aligned. Peel-ply covered the top and bottom to keep things from sticking and to leave a good surface for bonding additional layers. I setup the vacuum bag and sucked everything down to create clamping pressure and form the shape of the yoke. I also laminated a small rectangle of foam/carbon that will be used to connect the pads to the yoke. My vacuum bag was too small with not enough pleats, and so it pulled on the tape/leaked real bad, and did not suck down evenly. But i eventually made it work and left it under vacuum to cure overnight.



24 hrs later, I de-molded the parts. I trimmed the oversize parts to an even final thickness with the band saw, and it seems pretty stiff already. Now you can clearly see the laminated carbon/foam layers that will make up the core of the yoke.

Wow, that is pretty impressive. Looking forward to the next installment!

Last night I used a dremel and sanding block to radius the edges. I did some preliminary shaping of the pad supports, and found their location on the yoke. The plan is to make the pads as a curved surface, so I have to wait until they are infused before I can shape the bottom of the supports to match the curve.

I also cut slots for the yoke clamps and lined them with two layers of carbon: I wrapped the carbon cloth around a temporary foam plug so it fit tightly in the slot. I think this plus the stringers will be plenty strong to not be crushed by the clamp when it is screwed down tight.

Wow, at it again! Your engineering skills are impressive! to say the least! Can't wait to see the finished product - then you have to figure out how to mass produce them to sell to the rest of us!

This fall, your fellow Kruger Border Challenge participants will be jealous of the light weight yoke and the pounds you saved!

Grandma L: "...will be jealous of the light weight yoke and the pounds you saved! "

...unless it breaks halfway through...!

I got some more work done:

I made the shoulder pad blocks: I bent some plexiglass at a 12" radius to form a mold, and vacuumed the 3/8" foam with 2 layers of carbon fiber on both the top and bottom.



I also covered the yoke with a braided sleeve of carbon fiber for the 'skin' layer. This will take most of the structural stress. It came out of the vacuum bag with some wrinkles, but I filed and sanded them down. One of the photos shows it wet after I washed the sanding dust off. It is very stiff. Probably very overkill with all the stringers inside. I rested each end on a chair and was able to stand on the middle with no flex.



I also weighed things for the first time. There is still a little more carbon/epoxy needed to skin the pad supports, and both the foam pads and clamp hardware will add a little weight, but as it sits now, everything pictured here (yoke, pad blocks, supports) weighs a total of 13oz. So I think the weight saved over my old yoke will end up being several pounds.

Looks great - now, when will you be out testing it? And then, will you be taking orders? Videos please. Want to see it in use!

I'm hoping to have it ready for a May 20 bwca trip.

Wow, looking good!

I attached the pad blocks and supports to the yoke beam, and while it's not pretty, it is strong. It was difficult to apply carbon/epoxy to everything at once. I cut strips/squares of carbon cloth and wet each one with epoxy before applying it to the yoke. There were several complex curved surfaces all coming together, so it didn't want to lay down nice and flat- especially around corners. I put it all into a large vacuum bag and let it cure. I did manage to get everything stuck together in the right places, but the carbon cloth was all wrinkled all over, and it took a lot of filing and sanding to get smooth surfaces and curves again. That much sanding into the cloth ruins the carbon weave look, but I'm not too concerned about that. After sanding, the whole thing sits at 14.3oz. I mixed and applied 30g of epoxy for a 'hot coat' which is curing right now.


I also cut out the first layer of pads. I used 1/2" EVA foam that I cut from some leftover gym flooring. EVA is what most running shoe soles are made of. I used a router to make a 1/8" seat for the pad blocks and radiused the outer edges smooth. The rest of the pads will be 4" of synthetic batting squished down to 2" or so.

Not pretty? Beauty comes in many forms. Nice work.

Thank you for sharing your work. I've been amazed from your first post.

Finished!






First, I painted on a hot coat of epoxy to the sanded yoke. This gave it a protective gloss covering. If it was a show piece, I would sand and coat and wetsand and buff until the reflections were smooth and flat. But that would only add weight, and this is intended to be working equipment that can get beat up anyway. The weight of the bare carbon yoke is 14.4 ounces. I can stand on the middle and both the beam and the curved pads hold my 180lbs off the ground easily.



Next, I had to make the pads. I have previously used a material called HyperD300 to make reinforcement points on tarp corners. It is a polyurethane-coated nylon with a double-diamond ripstop grid that is waterproof and at 300denier is pretty tough, while being very light at only 4oz/sq yd. I ordered half a yard of 'khaki' color from ripstopbytheroll that is actually more of a gold. Back to sketchup where I modeled a rough pad and drew some patterns. I sewed the first one and it just didn't work out: but I could see what I had to change. I wasn't sure how to attach the pad to the carbon yoke, but came up with a tight drawstring design that held the pad in place without using any additional fasteners or hardware. The padding is the 1/2" EVA foam I showed earlier, and then 4" of synthetic batting I squished down to a total height of 2.5" or so. It's pretty firm, but cushy at the same time. This is the 4th set of pads I've made, but is a radical departure from previous versions. .

After attaching the pads, all that was left was moving the spring creek clamps over from the old yoke and drilling holes for the shock cords. The pads are pretty lightweight, but I was surprised at how the clamps were relatively heavy. The rubber grip was starting to peel from the pads, so I also added a piece of bicycle tire tube ala "The butthead mod". The final weight of the completed yoke is just over 28 ounces (1.8 lbs.). Previous yoke was 4.6 lbs so a total weight loss of 2.8 lbs. It gives a nice 3.5" lift over the old yoke, too.

Can't wait to hear your review - how it works on your upcoming trip!