A Beginner Builds a Kayak
I would like to build my own kayak. I have made some adirondack chairs and a window bench, so why not a boat. I know very little about boat building. I have an engineering degree from the US Merchant Marine Academy, but I don't think much that I learned there can be applied here. My husband found the website Yostwerks.com - this site is a great start. It has plans and photos and offset tables and it's all free. I decided to build the Sea Bee 13. This is the drawing from Yostwerks.com with some additional labeling.
After deciding to build this boat, I became very apprehensive. I had no idea where to start. I was already planning how I was going to paint the skin and I couldn't even read the offset tables and draw my cross sections. I searched the internet and didn't really find anyone providing set-by-step instructions for someone with as little knowledge as me.
So, here's my take on how to read an offset table and draw a cross section.
An offset table is a list of x,y coordinates that when plotted, form the outline of a cross section of a boat. Here's how I interpreted the second cross section of the Yost Sea Bee 13.
The row for section 2 gives the coordinates for the keel, chine 1, 2, 3, the gunwhale and the deck ridge. The x, y coordinates can be found in the columns labeled HAB and HB. HAB means height above baseline and is plotted on the y-axis. HB means half-breadth which is kind of like width and is plotted on the x-axis. HB is plotted on both the + and the - sides of the axis so the shape is symmetrical.
To start, draw an x-y axis. You can create templates on large graph paper or on your computer, but I just drew them directly on my plywood. I used two 2 foot by 2 foot pieces of 15/32 inch Sanded Pine Plywood Exterior Grade. Some people recommend marine grade plywood, but I couldn't find any at Lowes or Home Depot. So, draw your axis and plot the first three coordinates.
Keel: no entry for HB and 1.46 cm for HAB or 0, 1.46 which means right 0 cm and up 1.46 cm
Chine 1: 12.74 for HB and 3.2 for HAB or +12.74, 3.2 which means right 12.74 cm and up 3.2 cm
Chine 2: 19.93 for HB and 6.37 for HAB or +19.93, 6.37 which means right 19.93 cm and over 6.37 cm
Draw all the coordinates and connect the dots. Now you have the outer most edge of your second cross section.
It's time to allow for the stringers. According to Yostwerks, the stringers need to fit within this outline. After some debate, I chose to use 3/4" by 3/4" stringers at chine 1, chine 2, and chine 3. I placed the cut out for the stringer with the outermost bottom corner at the intersection of HB and HAB. I used 1-1/2" by 3/4" for the gunwhale and the deck center. The stringer at the gunwhale should be 1-1/2" from the upper outside corner and then should be sanded smooth with the top of the cross section. The stringer at the deck center is going to be notched out 3/4" so I'm only cutting out 3/4" of the cross section to allow for it. The keel sticks out from the boat, so only cut out 3/4" of the cross section.
A skin on frame kayak has the outer skin laying on the stringers, so you have to remove some material between the stringers. I planned to remove 3/8 of an inch between most. At the keel I removed 1/2 inch on a curve. Also, I wanted to cut out the center to allow for my legs and to make the kayak much lighter. These numbers are based on other kayaks from the Yost website. Since they are used for other kayaks, not the Sea Bee, I'm hoping it works out.
Now do the same thing for cross sections 1, 3, 4, and 5. After everything is drawn, cut it out. We did this in the garage. My husband drilled out the inside corners while I cut with the jigsaw. It was fairly easy and went twice as fast with the extra pair of hands.
A Multi-Chine Skin On Frame Yostwerks Kayak
After cutting out the inside on all the cross sections, we cut out the outside. I think it's better to drill your holes in the stringer cutouts before cutting the outside completely, we had less tearing of the wood.
Voila, five stringers completely cutout. They don't seem like enough to be the basis of a kayak, but I do want it to be light. Just a note about the deck stringers - I drew in one forward of the hatch on cross sections 1, 2 and 3. On cross sections 4 and 5, I drew in 2 cutouts for deck stringers. I'm not sure this is necessary, but that's what I saw on other kayaks. My husband thinks I placed them too far apart, but I was not really sure where to put them.
Now to build the strongback and cut the stringers.