Ultralight Kayak - Middle School Project

This is a skin on frame kayak that was made as a prototype to make with my middle school woodshop class. There are some great advantages to a kayak of this style! It was relatively cheap (~$300), no epoxy (less toxic) and is extremely light (~25 lbs). My students have started building there own in groups of only 4 students! I will continue to update this with their work too.

Tools

• CNC or scroll saw for cutting out frames
• Table saw or circular saw
• Hand plane (spoke shave helps if you have it)
• Hand saw
• Drill
• Countersinking drill bit
• Wood file
• Large sewing needle
• Laser level (string and level substitute OK)
• Spring clamps
• Bungee cord

Materials

• Marine plywood 1/2" 4'x8' is more than enough (or exterior ply NOT exposure ply)
• 3/4" clear (no knots) cedar or redwood to be ripped to dimension
• White oak (for combing ~85"x6")
• nylon sinew
• 1/4" oak dowel. Or my students will use 1.75" 316 stainless screws since there will be less chance of plywood blowout when drilling. Must be 316 to be around salt water. If not going in the ocean it is up to you.
• Gorilla glue
• Spar varnish
• Kayak nylon fabric. This is what we are using
• Strongback materials
  • 2"x2" lumber (~60' + scrap is nice to have for other steps)
  • 3/8" Plywood 4'x8'(Any thickness works)
  • 3/8" screws

References and sources

The hull design is the Sea Bee model from Yostwerks. There are many great free designs on this site. It is a mirrored site, the original author seems to be MIA. The mirrored site sometimes moves. If it does not work try this ;). Some of the designs are more complete than others. Very detailed. I recommend checking it out.

The skin stitch up method was from Cape Falcon kayaks video that can be found here. He is much more of an expert on the topic than I am.

The strongback is simply the long narrow table that the kayak will be built on and temporary mounted to for alignment.

For this kayak the strong back can be 12' long. It will be a 13' kayak and you will have the ends hanging off. This will be fine. Any long straight beam similar to this will work. This one is made from cheap plywood and 2x2s. The ply was ripped down to 6" (my students will be using 5"). The 2x2s are not always straight so as they were being screwed to the plywood they were pushed or pulled to be in line with the straight cut edge of the plywood to ensure that things came out relatively straight.

This was all made with 8' lumber and ply. To get to 12' the 2x2s butt joint was in the center of the plywood and the plywood butt joint was in the center of the 2x2s. This can be seen in the photo. This is important to mention to middle school students!

The legs can be rigged up any way you like with scrap or just put the whole thing on a table or sawhorses. I have a video of what I did. Just make sure it will not tip over!

The hull design came from Yostwerks as was previously mentioned. The original designs and offsets can be found in the images. I digitized the frames in Fusion 360 so that they could be cut out on or X-Carve CNC. This F360 file can be found here. If you are using an X-Carve too use these. Frames A and the second set Frames B

The frames could also be cut out on a scroll saw or jigsaw. The Yostwerks site has detailed instructions on this. What I am doing with my students is cutting out frames from MDF that they will be using a contemplating router bit on to make their frames faster than the CNC can.

The corners of the frames will need to be cleaned up and made square for the stringers later as seen in video.

This is potentially the most important step! Take you time!

The spacing of the frames will be measured and marked on the table. Before mounting frames make sure that the risers that will be holding the frames are perfectly vertical and in line with each other. It is important to stay consistent with the side of the risers that you mount the frames to so that the spacing remains true. I used a laser level for alignment of the frames and to place them at appropriate heights. I chose to align them all off the bottoms of each frame where the keel will be later.

Keep the frames in place temporarily with spring clamps. Once you are satisfied with placement the frames are screwed to the risers to keep them in place.

The stringers are all the longitudinal pieces of the cedar or redwood that run the length of the boat. Some have special names like the keel (bottom center piece), gunwales (side most members) and chines (the pieces that are between these).

• The gunwales will need to be 1.5" x 3/4"
• The rear deck members will be 3/4" x 3/4" (length to fit on these)
• All other stringers will be 1" x 3/4"

These are all temporary fit in this step and cut long for now (14'+). They will have to be cut by hand later. They can be temporary bungee corded in place. If they do not all fit right now because the risers are in the way that is OK. Just leave for later when the boat is flipped over.

These are the bow and stern of the boat that will be made of the same ply that they frames were made of.

The shape of these were made to fit based on the drawings from Yostwerks. With the bungee cords holding the stingers in place a piece of plywood was held between them and the shape was sketched onto them. This was not over thought. It was just made to look about right with the angle of the stringers that later will be joined to it.

I will be making a template and CNC file for my students soon and will update this step.

There are two different things that need to be shaped and adjusted here. The frames need to have a correct angle on them so that the stingers that are bending sit flush in them. This can be seen in the videos and done with a file.

These are small adjustments but important for a strong joint.

This step needs your full attention.

The stringers will be cut to the correct angle so that they join the stem at the correct angle. This will be a compound angle. Basically meaning there will be two different angles if measured on different sides.

The stringers were all moved down to one end so that if we need more wood the excess is not cut off. We are doing all of one end of the boat first. The stingers are being held up against the stem as the angle is transferred as seen in the video.

Do not expect this to be perfect. You will need to hand plane this to fit. The best way to do this is to put a block behind the stinger as you plane it as seen in the image. This stops the stringer from bending as you work on it. The two sides of the kayak should be symmetrical as well. You will want a flat mating surface between the stem and stringer, outside of that "eyeball it" and make it look nice.

Topside stringers and the keel can also be cut to length as seen in the image. There should be significant overlap of the keel onto stem with a notch cut out of the stem for the keep to fit. I decide to stitch these members to the stem. Not really necessary. Dowels or screws could have been used. Keep in mind that the keel will be shaped down later so screws will need to be removed later or counter sunk deep enough that shaping is possible.

All gluing will also need a fastener (screw or dowel) to help hold the joint. Gorilla glue was used and the wood was sprayed lightly with water before applying. This is needed for this type of glue.

The video shows the joint at the stem with a dowel through the stringers. A dowel works better than a screw for the stringers since it may need to be filed later and shaped. The video also shows how the boat was flipped and remounted to the risers to allow for the keel and other stringers to be mounted.

Fasteners should have pre-drilled counter sunk holes so that the screw does not split the wood and sits flush with the surface. In the video they were temporary. Test everything with screws only (no glue) and once you are satisfied apply glue and do the final mounting.

If you are using dowels glue everything with screws first and once dry remove screws and ream (re-drill) the holes for the 1/4" dowel. Apply glue and tap it in.

**I decided to stitch the keel and the deck stringer to the stem. This could have been done with screws or dowels. I was just having fun getting carried away.

there are many square edges on the boat that you will want to round over. The stem and keel will have the most work to be done. I touched many of the stringers just a little so they would not wear on the fabric later.

I also decided to cut a notch out of the bow and stern so that a piece of hardwood (oak) could be glued in. This was done to make a "bumper" if I hit anything. This piece will also need to be shaped.

This step seemed like a bit of overkill to be but each frame to stringer and stinger to stem joint was lashed together with sinew as tight as possible. I lashed these with a needle to make tying off easier.

I do not a many photos of this step but this is the hoop that you will sit through. The X-Carve file can be found here for the template. The template was cut from 1/2" MDF with extra blocking glued in to give it more thickness. Holes were drilled to allow for the spring clamps to clamp to.

The wood used was white oak. This is because it is strong and bends well. Also it holds up in marine environments. Red oak is not the same thing.

You will need everything to be cut to 1/8" thickness. Two pieces will be 1.5" and four will be 1/4" (or 3/8" if you are cautious).

Starting with the 1.5" pieces they will be bent around the form and glued together. As the two ends come back to meet they should join in a scarf joint as can be seen in the close up. Only one side will need the taper. Let the other end overlap. Once the glue dries plane it off to shape. This means only one layer can be done at a time.

1. Plane taper on one end
2. Test clamp
3. Glue up
4. Clamp
5. Wait
6. Plane off excess
7. Repeat.

Try to stagger the location of the joint. This will make the combing stronger.

The video done by Cape Falcon Kayaks tells it better than what I can say here.

One Issue that I had was that I did not wet down the fabric when fitting it. I noticed later that this was recommended. I ended up with a little extra in the center and need to take some tucks but it ended up OK. This can be seen in the photo around the combing.

We are using nylon and painted it down with Man-O-War spar varnish. The step about dye in the video we are not doing. The last image shows how I hung the boat so that it could be varnished. There is simply a 2x4 inside the boat it is resting on. I did 5 coats of varnish. The first did not get full wet out which made some parts blotchy.

I embroidered the name of the boat into the side as well, just for fun. I sketched it with pencil first.

Serotonin + sea = "Seaotonin"

This seat is something I just slapped together to be able to use it. So far I have been very happy with it. The seam down the middle is so that it sits on 3 stringers not just two like a flat board would. All the string is just to keep it in place without the need for drilling holes or anything I can not reverse later. I put the sinew through the holes in the frame that mounted the boat to the risers before.

Hope you enjoyed it! The whole project took me about a week + varnishing time over the teacher summer vacation. This is not my first boat and I have been doing woodworking for over twenty years so don't worry if it takes you longer.

This is a vary achievable project for most people. If you do not have a CNC take your time cutting the frames out. After that there was not a lot of fancy foot work.

Don't be intimidated by the frame. If you skin it correctly almost anything will float!

Sea you out there!!!