Although I had never actually kayaked before, one day I decided to make a stitch and glue kayak. For a non-kayaker I'm not sure why, but it had to do with a rowing class I had taken once, and I wanted to get out on the water on my own boat. Also, building a rowing shell seemed difficult, better to start with a kayak.
For those of you who don't know, stitch and glue is a well established method of building all kinds of boats. It involves cutting plywood into the right shapes, stitching the shapes together with wire, and then permanently gluing the whole thing up. A quick web search will yield loads of info about it.
There are some really nice kayak building kits out there, and you will definitely get better results than I did with a kit, but I'm pretty happy with how my kayak turned out. Also the kits can be a little pricey and I am going cheap. These online sites also sell plans which are much cheaper than the kits: Chesapeake Light Craft, Pygmy Boats, One Ocean Kayaks, and Shearwater Boats.
There's a few free kayak plans on the internet. There's one called the Guillemot and there may be some here, here, and here, but I chose the Sqeedunk C-16 because it looks a little easier to assemble. Now these aren't exactly plans, they're really just points you mark out on the plywood, then play a interesting game of connect the dots.
Another option for the true DIY'er is to design your own kayak using FreeShip, DelftShip, or your favorite 3D CAD software. Just be sure it is capable of unfolding curved surfaces, so you can take the curved panels you design and flatten them out for the plywood. A word of warning: CAD software typically has a steep learning curve. You may end up spending a lot of time working at the computer.
For materials, you will need some thin plywood. Everyone in the kayak biz will tell you to use okoume marine grade plywood, and they are right. However, since I'm going cheap and I just want a recreational kayak I can play around in rather than a serious sea kayak, I bought two nice looking lauan 4'x8' pieces at Home Depot. They are sometimes called door skin and are about 1/8 in. thick. Here's a tip, use a flashlight to shine light thru the plywood and look for gaps or voids in the middle. Voids are bad.
To start off with I bought, 30 ft of 6 oz. fiberglass cloth, a gallon of epoxy resin and half gallon of hardener from this online site. I also bought several feet of solid copper wire at the hardware store. It was red and white 20 gauge wire for antennas I think. Make sure it's solid, stranded wire will not work.
This was a really long project, it took me around 8 months, but there were weeks that I didn't get any work done. If working on it full time, it could be done in less than a month.
For tools, I used a coping saw and key hole saw to cut the plywood although some people recommend the japanese style pull saws. A power circular sander is a must. I used many a 60 grit sanding disc. You will also need a seemingly endless supply of sand paper, disposable brushes, and latex gloves. Other tools: rasp, carpenters square, drill, utility knife, safety glasses, pliers, etc.
Step 1: Scarf the Sheets
The boat I chose to build is a 16 footer, but that's way more boat than I need and I don't want to store a 16 foot boat. Also it would require attaching three 4x8 ft. pieces of plywood together. I decided to shrink the boat down to a more manageable size, but more on that later. Shrinking allowed me to attach just two plywood sheets together.
To create the edge, I took a 2x4 board, and placed a scrap piece of plywood on top of it. Then I placed one sheet pretty side up on to the stack, and the other sheet pretty side down. This way the pretty side doesn't get damaged during the scraping and sanding. The boards are offset by 2 inches then I placed blue tape 2 inches from the edge of the top sheet to let me know that I should not cut into that part. I used a C clamp to keep the stack from moving. Then rasp and sand it down to a nice smooth slope.
I kept as much saw dust as possible to thicken the epoxy later in the build. The thickened epoxy is useful for squishing into the corners for a stronger joint.
Glue it together. I used water resistant wood glue because I was waiting for the epoxy to arrive, but I regret it. Using epoxy will blend in better with the later epoxy coatings. I swept the floor and laid down some plastic wrap to avoid gluing the sheets to the ground. I then placed the bottom sheet down and applied glue. Next came the top sheet followed by another layer of plastic wrap. Finally I topped it all off with scrap plywood and weights to make a tight bond. Let it dry for a day and you should have one long 4x16ish sheet of plywood.
Step 2: Connect the Dots and Cut
To reduce the kayak from 16 footer down to a 14 foot boat. I moved to points at the back and front of the boat closer together lengthwise. I left the middle area alone however, because that's where you sit and I didn't want to squeeze myself out of the boat.
To get a better idea of what my new kayak will look like and how it's supposed to fit together I plotted out the points onto a piece of cardboard. I converted each inch to a 1/8 in. and made a scale model. After cutting out the pieces I used hot glue to build it. This gave me the confidence to do it for real.
Once the points are plotted out on the plywood you need to use something flexible to draw between the points. It's a straight edge that you can bend. I believe the process is called fairing with a batten. I used a straight thin piece of sheet metal and for the sharper curves I used a smaller piece of plastic. It's also helps to have two extra sets of hands. In lieu of that, I used a couple bricks to hold the batten in the right spot.
Remember to measure twice and cut once. Cut the wood as accurately as possible and minimize the splintering by using a finer toothed saw blade. Once cut, clamp the opposite sides together and sand them so they are the same shape. It's also a helpful to round off the edges on the ugly, interior sides of the panels so they fit together better.
Step 3: Stitch
Start putting in wire stitches about every 6 to 8 inches. Use a drill to make a hole small enough for the wire to go thru about 1/2 in. from the edge. Leave them lose at first then tighten up as you go. Some areas will need more stitches than others.
Step 4: Glue
I bought the epoxy with pumps for measuring it out. It's a 2:1 system so pump twice for the resin and pump once for the hardener and mix it in a disposable plastic cup. Epoxy is a sensitizer meaning that it wont immediately harm you, but in time you will develop a reaction to it. It's best to use latex gloves when applying it.
This is the point where I had to decide whether to leave the copper wire in the boat or remove it. It's perfectly ok to leave the wire in and cut off the excess, but I chose to remove it. Leaving the wire in is actually a much faster method.
First I glued the seams and let it cure. Then I separated the top and bottom half and added thickened epoxy in between the wires. Just mix saw dust into the prepared epoxy until it becomes like peanut butter consistency, then squish it into the seam. If you want the thickened epoxy to match the rest of the boat, you will have to experiment by combining the epoxy with different combinations of saw dust, silica, glass microballoons or whatever. Once it was cured I could begin cutting and removing the wires.
Since the seams already contain hard thickened epoxy I had to sand it smooth. When sanding epoxy be sure to where a mask, and eye protection. Since I work outside under the porch I was already in a well ventilated area. At this point I also cut out the cockpit. I used a couple of buckets and straight edge to draw the curved cockpit shape I wanted. Another technique is to tie a string to a pencil and draw the arc. When it looked right I cut it out.
Next you can either tape the seams which is what I did, or you can fiberglass the interior of the boat. To tape the seams, I created 3 in. wide fiberglass tape by cutting the 6 oz. fabric into strips of whatever length I needed. Once the interior was sanded, I added more thickened epoxy to where the wires had been, and before it dried started laying out the fiberglass tape. To wet out the tape I just poured a little epoxy on the tape and spread it out with a brush. Also at this time it's a good idea to paint the interior with epoxy. When water gets into the boat, the epoxy coating will prevent it from damaging the wood.
When the top and bottom sections are complete it's time to join the two halves. Unfortunately they didn't fit. It's probably because of the modifications I made to the design or it could have changed shape when the two sides were separated, but regardless I had to make it fit. The middle fit together just fine, and I was able to stitch it together with copper wire and glue it. The ends however would not come together, so I added some weights and mashed the ends together then filled any gaps with thickened epoxy. The deck actually stuck out about a half an inch over the edge on the front and back ends. I ended up trimming back the over hang and putting thickened epoxy in the gaps.
After the epoxy cured I could remove the side stitches. Reaching into the cockpit I was able to cut most of the wires. The rest of the wires I was able to work out with some needle nose pliers. Taping the final two seams requires you to go in the cockpit with a stick and a flashlight and push thickened epoxy into the seams. To get it into the very ends though, I made some thickened epoxy that was a little runny and let it flow down the seam by propping the kayak up at angle. Next comes the tape. This time I wet the tape in epoxy prior and rolled it down the seam by pushing it with a stick.
Step 5: Fiberglass
First paint the bottom of the boat with epoxy. This allows the wood to absorb some of the epoxy and makes wetting out the fiberglass fabric easier. Also it allows you to see any defects you over looked. Then while it's still wet, drape the fiberglass cloth over the hull and wet it out. Pour the epoxy on to boat and spread around with either a brush or a plastic spreader. Once the bottom is dry, cut off the excess fiberglass, sand the edge, flip the kayak over, and do the top.
Use small batches of epoxy. In a hurry I made a double batch and it heated up and turn into a hot gelatinous mass of unusable epoxy and it melted the plastic cup.
To get a smooth finish, sand the kayak, apply another layer of epoxy, and repeat. This can be done while working on the rest of the steps.
Step 6: Coaming
My coaming is made by bending plywood around the inside of the cockpit then layering more on. First I soaked two 5x48 in. plywood strips overnight in water to make it more pliable. Then I was able to push the strips into the cockpit so that they run along the inside on the left and right side. I was able to trim it so that the pieces fit very snug into the cockpit without any clamps. After it dried in position, I removed it and stained it to match the side deck panels. Unfortunately, the plywood shrunk just a little bit when it dried. To make it fit I had to add in a small strip of plywood. Once it fit I glued it in.
Next I sanded and fiberglassed around the outside edge to add some support. To build up the lip I started layering strips of plywood around the cockpit. Bending and gluing each strip one at a time. This is where lots of clamps come in handy. I used clamps made from PVC pipe, and there's even an instructable for it. To add more strength, I put in another layer of plywood to the inside edge of the cockpit and then fiberglassed the inside edge. I then sanded and shaped the coaming.
Step 7: Hatch and Bulkhead
Since the lid will now fall thru the opening I have to build up a place where the lid can rest. I glued two layers of plywood under the deck. The first layer is a spacer layer, and the second layer is wider to allow for weather stripping to go around the hatch. The weather stripping of course prevents water from entering the hatch. For the first layer, cut two 'C' shapes about an inch and half thick that conform to the hatch opening. Then cut the second layer the same shape but add width for the weather striping. Coat the pieces in epoxy then clamp them in place. I also squished thickened epoxy into the cracks.
Bulkheads in a kayak add strength to the entire structure, and also provide a water barrier. It's basically just a wall inside the boat. If you get a leak in one part of the boat the bulkhead will prevent the water from flooding the entire craft.
My bulkhead was somewhat of an after thought and since it's a smaller boat I only added one right behind the cockpit. The shape involved a bit of guesswork. I measured the panels where the bulkhead would go and sketched out what I thought would be the right shape on plywood. After cutting it out, I tried placing it inside the boat where it should go, but it didn't fit. I then started trimming it down until it fit in the right spot. I painted it with epoxy and used thickened epoxy to seal any gaps around the edge.
Step 8: Finishing Touches
To finish up the cockpit I fiberglassed the floor where my feet would go and added plywood hip braces on the sides for a snugger seat. Also the hip braces provide a place to attach the back rest strap. The footbrace mounting kit came with instructions that were pretty straight forward. It's the no-drill type that just glues to the inside of the kayak.
To attach the bungie cord and backrest I made my own padeyes out of glued together plywood strips. I simply stacked five 24x1/2 in plywood strips together with epoxy and clamped it all together. When it cured I drilled holes for the bungee cord, and cut it into 2 in. sections. I used a bench grinder to shape it then sanded it smooth. For the hatch I was able to clamp the padeyes to the deck, but in the front section I had to just glue them to the deck without clamps.
I made the holes in the front and rear of the kayak extra large so I could feed a chain thru it and lock it to something if I needed. I used a hole saw to make the holes then used brown packing paper and fiberglass to seal it up. I made a tube of packing paper about 1/8 in thick, then cut out some fiberglass that would cover the inside and outside of the tube. I then rerolled the tube while wetting it with epoxy and putting fiber glass on the inside and outside. Once the tube was slightly smaller than the kayak holes I fed the tube thru the holes and tried to enlarge the tube so that there were no gaps between the tube and the kayak. Once the tube cured in place I cut off the excess and of course there were some gaps that I filled with thickened epoxy. After sanding it out, it turned out pretty well.
Once the kayak is as smooth as you like and all the fittings are glued in place it's time to add varnish. The varnish protects the epoxy from sun damage and also adds a nice shine. I bought some gloss spar varnish from the hardware store and stuck it everywhere the sun will shine including the cockpit interior. Don't however forget the remove the bungee cord, seat, and backrest first. When it dried I lightly sanded it with some fine sandpaper then applied 2 more coats. Be sure to do it in a well ventilated area and wear a mask when sanding and applying the varnish.
If you are like me it took months to finish this sucker and it's time to take it out. Grab yourself a paddle and a lifejacket and test it out. Lo and behold it floats and floats well. The kayak ended up weighing in at 37 lbs and is 14ft. 2in. So far, I've taken it around the local lakes, and down the lower Salt River once. So far no leaks. I scraped the bottom a couples time on the river and it fell off the car once (Oops), but it's easy to fix. Just sand it, apply more epoxy if there's any left, and add varnish.