Introduction: Refurbish a Skin on Frame Kayak
Living in Cambridge near the historical Charles river and watching people kayak down it's length, I nurtured a growing desire to be able to interact with the natural structure on my own schedule. I decided to build a boat, but I didn't know how to get started. I soon received an email from a friend of a friend who owned a derelict wooden kayak frame that he no longer had time to repair. Instead of seeing it go to the trash, I decided to repair it and make it my tool to become more in touch with nature.
There are different types of kayaks, however the simplest and cheapest type I could find is known as a "Skin Boat". This was historically realized by a lightweight wooden skeleton that is tightly wrapped in stitched together animal hide. As materials improved, the material changed to chemically sealed canvas and eventually plastic sheets, such as nylon and etc. Also, staples were invented and the fabric was stapled to the frame instead of stitched on. This lead to faster manufacturing of the boats, but this also reduced the resilience and reparability of the boats. As the frame materials shifted from wood to metal, and even polymer materials, staples could no longer be used. This prompted a return to the historical practice of stitching the fabric to the frame to tension it and hold it on.
This is the design that I decided to replicate as I refurbished the vessel. This project would not have been nearly as successful without the help and facilities of the MIT Electronics Research Society (MITERS) and MIT's D-Lab. MITERS is a student run shop where tinkerers of all kinds gather and build cool things. D-Lab's mission statement is "Development Through Dialogue, Design, and Dissemination," and they specialize in creating solutions to problems in underdeveloped countries.
An Epilog Zing 16 Laser would allow me to build more interesting large scale things, and to tinker more effectively in general. Through this project, I learned how to reinforce joints with carbon fiber. My next goal is to build a lighter boat from laser cut materials that are reinforced with carbon or glass fibers, as well as a cardboard surf board that is wrapped in structural fiber as well.
Step 1: Table of Contents
2. Table of Contents
3. Frame Inspection
4. Repair process and BOM (Part 1 & 2)
5. Skinning process and BOM (Part 1-7)
6. Concluding Thoughts
Step 2: Frame Inspection
After finding the frame, I inspected it for damage and to see what needed to be removed during cleaning. Many of the wood glued joints had failed, and the beams separated. The rub rails were no longer required (for the most part), but the screws holding them on had rusted and broke when removed. These broken screws left sharp points along the frame that could tear or puncture the skin later on in the skinning process. The old skin on the frame was a vinyl material that was held on with many staples which had also rusted. The old waterproof urethane coating on the frame had deteriorated in many spots, and needed to be stripped and reapplied. Finally, many of the joints and lengths in the frame had rotted and the subsequent screw fasteners were no longer effective.
Step 3: Frame Repair
Repairing the glued joints was straight forward. I sanded down both sides of the broken joints to remove the old glue and insure a good surface, glued them together again and clamped them.
To remove the rub rails, I unscrewed most of the fasteners and bored out the ones that were stripped. Many heads broke off, but I was able to remove the rub rails nonetheless. To remove the old skin, the staples were pried out with a flat head screwdriver and then pliers were used to pull the skin out through the penny nails that were holding it on.
I used a Dremel to remove the sharp edges from the frame left by the screws, nails and broken staples.
I stripped off the old waterproof urethane coating with a chemical solvent. Then, I scraped off the remaining urethane with a putty knife and sanded down the frame to ensure that all of the old coating was removed. Then I painted on three coats of urethane/wood stain and sprayed on an additional layer of urethane for added resistance. I wore nitrile gloves and a face mask while sanding and applying the stain and urethane to the frame.
To repair the heavily rotted lengths of the frame, I used carbon fiber twine. I weaved epoxy impregnated twine around the thin frame sections to lash the broken joints together and I wrapped the rotted length in three layers of carbon fiber twine to form a rigid sleeve. I used the non-stick side of electric tape to hold the carbon fiber on.
Step 4: Frame Repair (Part 2) and BOM
I was unable to easily use carbon fiber twine to repair the rotted and split floorboard of the boat. Instead, I heavily sanded down the split section. After I sanded down the sections enough to achieve decent surface contact between the two halves without a large gap, I applied a heavy bead of wood glue to the joint and clamped it together. Then, I drilled three counter bored pilot holes through both clamped halves and clearance holes through the piece that was to come in contact with the screw heads. I then inserted wood screws coated in wood glue, which were longer than the screws which had rotted, to ensure that they had a firm grip in the wood. The glue coating was to ensure a seal between that screws and the wood that keeps water from seeping into the holes. After this step, each screw head was covered in wood glue and varnish to re-seal the newly drilled wood.
I didn't need to use wood glue at all to repair the rotted through stringer joint, other than to seal the screw threads and head. I removed the rotted fastener, realigned the pieces with some clamps, drilled a pilot hole with a greater diameter and depth than the prior screw, and inserter a larger screw in its place (still sealed with wood glue and varnish).
At this point, I was done repairing the frame. Before stitching the skin on, I inflated some bags and put them in the front and rear of the kayak. Their purpose is to keep the frame buoyant in the event of tear in the skin. This is very important, especially if your frame is made with a material that is denser than water, which will sink in the event of a tear. Even a wooden frame probably isn't buoyant enough to support the weight of it's crew if the skin is torn.
- Wood glue
- Nitrile gloves
- Disposable mask with mechanical filter (at least)
- Carbon-fiber twine
- Wood screws (lengths vary by frame design)
- Extra fine sandpaper
- Exterior urethane wood sealant
- Chemical urethane solvent
- Power drill and driver
- Dremel and sanding attachment
- Bolt cutters
- Flat head screwdriver
- Natural fiber paintbrush
- Putty knife
- Extra Fine Steel Wool
- Drill bits for pilot holes
- Light file
Step 5: Skinning Process (Part 1)
I will explain how I skinned my frame, then at the end of my explanation I will leave you with a link to a Youtube video of somebody doing the process in real-time:
Drape the canvas over the upside-down boat and align it so that it drapes over all sides ends. Check to make sure that there is enough fabric to wrap around the whole boat before you start cutting and sewing. Pin one side of the canvas to the boat as shown. Cut the pinned side with a hot knife, I used a soldering iron with much success. You must melt the ends of the fabric that you cut or you could end up with weak stitches that come apart. Do the cutting in a well-ventilated room to avoid inhaling too many noxious fumes from the melting fabric. Trim the fabric on the pinned side until you have around .5” of overlap down the centerline of the kayak. Start .5 inches behind the cut with a whip stitch, I used dental floss as thread and a curved needle, and continue all the way to the bottom. Tie off the thread with a French knot. Sew a running stitch along the top edge of the boat, now facing down. Sew down around 3” and double back to the tip, ending with another French knot, to form a pocket in the fabric. Unhook the pocket, move to the other end of the boat and pull the fabric 1.5-2 inches towards you before repeating the process to create another pocket. Now, leaving this pocket on, go to the other end of the boat and stretch the fabric to pull the second pocket onto the end. To do this I angled the boat downward, sat on the ground and braced my feet on the frame to pull the fabric over with one or two strong tugs.
Step 6: Skinning Process (Part 2)
Flip the boat right side up and trim the excess material over the deck beams to about .5 inches of overlap. Use twine to quickly tighten the skin on the frame with stitches that are spaced 4 inches apart. I used a large straight needle and 1.5 arm spans of seine twine for this step. Tighten this thread after the stitch is done and tie it to itself with a half hitch knot. Re-trim the stretched fabric until around .5 inches of overlap along the centerline of the boat.
Step 7: Skinning Process (Part 3)
Using the whip stitch from earlier with the small thread and curved needle, sew up the sides of the boat to remove the tension from the twine. Be sure to pull the thread tight between stitches. This should pull the fabric taught, making it almost as tight as a drum. I didn't have enough fabric to totally cover my boat, so I had to make some patches from the trimmed fabric. These patches were sewed on with a cross stitch.
Step 8: Skinning Process (Part 4)
Trim the excess material around the boat’s cockpit. Depending on your boat design, some use a coaming, stitch the fabric taught around the cockpit. Because my boat was designed to have the fabric stapled on, stitching the skin to the cockpit wasn’t straight forward. I decided to pull it taught using the same process we used to initially tighten the fabric around the top end of the boat. With the twine and large diameter straight needle, I made 4 inch stitches parallel to the cockpit to pull the fabric taught over it. After I finished the stitches on both sides, I trimmed the excess material with my soldering iron.
Step 9: Skinning Process (Part 5)
Because I had to improvise in attaching the skin to the cockpit, the top part of my boats skin was loose on one side. To fix this aesthetic issue, I sewed in a dart to pull the fabric taught again. I don't have a great picture of this, but you can see it if you look closely. My darts are whip stitched lines up the sides of the boat, parallel to the spacer at the front of the cockpit. The dart pinched 1 inch of fabric together to make the skin tight on the top of the boat. I created another dart on the other side of the boat to keep the look symmetric. This step isn’t necessary, since it doesn’t affect the smoothness of the skin on the bottom of the boat. However, this does make it easier to speak the urethane on the skin when it is time to seal the fabric.
Step 10: Skinning Process (Part 6)
Here is a YouTube video of someone skinning a kayak in real time, he also talks through his bill of materials. This was an invaluable resource to me.
Step 11: Skinning Process (Part 7) and BOM
I will explain how I sealed the skin on my frame, and at the end of my explanation I will leave you with a link to a series of videos of somebody doing the process in real-time.
I mixed small batches of urethane and spread it on the upside-down boat. Using a plastic card, I squeegeed three layers of the urethane on the bottom of the boat, working clockwise with ~10 minutes between layers. The order of operations were to mix a batch urethane, coat the underside of the deck-beam using the squeegee, coat the top chine/panel on one side of the boat using the squeegee, coat the lower chines/panels on the same side of the boat using the squeegee, then use a paintbrush to spread a very thin layer of urethane in and on the seam at the ends of the boat. Next I repeated this process on the other side of the boat, except for painting the deck-beam. I did this three times total and then spent around 30 minutes cleaning up drips and runs until the urethane had set up enough to stop dripping. You will want to ensure that the urethane does not run onto the underside of your boat and dry, or you will have bumps of dry plastic when you finish. This is only cosmetic and it is easy to prevent by simply smoothing out the beads that run onto the underside of the boat with your card until the liquid stops dripping. After letting the underside of the boat dry for a few hours, flip the boat right side up and repeat the process. I ran out of urethane, so I was only able to do one full coat on the top. The fabric at the top leaks, however the waterline does not get this high since the hull displaces a lot of fluid.
- Two large, straight sewing needles
- Two large, curved sewing needles
- Two boxes of unwaxed dental floss
- One roll of number 21 seine twine (http://shop.skinboats.com/Seine-Twine-21-sein21.ht...
- 850 Denier Ballistic Nylon, to skin the boat (http://shop.skinboats.com/Skin-Boat-Fabric_c3.htm)
- 2 Part Urethane, to seal the boat (http://shop.skinboats.com/2-Part-Urethane-Coating-...
- 4 Natural fiber paint brushes
Step 12: Conclusion
At this point you should have a floating, skin-on-frame kayak. I urge you to purchase a life vest for yourself and everybody in the boat. Not only is this the law, it is the responsible thing to do.
Also, test the boat in shallow water to be sure that your urethane coat does not have any leaks that you need to repair. I threw together a quick cart to transport the boat for testing and use, however I ended up using a smaller, better made one out of convenience. To build the cart, I nailed four caster wheels to the corners of an unused shipping pallet. For testing, I set the boat in a river and watched it for ~15 minutes to be sure that it didn't have a slow leak. Next, I sat in the boat for ~15 minutes in shallow water to be sure it could hold my weight.
The last step is to learn how to re-enter a kayak alone, in the event that you flip over while in deep water. The linked video should get you started down the right path.
That's it, now you are ready. Happy yakking!!!