Step 1: Materials
I like to get my oak boards in 3 inch widths, 5 to 8 foot long. I pick through the boards to find ones that have flat grain that runs straight for the whole length of the board. The longer the board, the less likely it is that its grain is going to be straight for the whole length of the board. The boards should also be free of any irregularities in the grain.
Ribs need to be about 8 inches longer than the width of the gunwales where they are being inserted. For estimation purposes figure an average of 24 inches per rib. Lets say you buy boards that are 5 feet long and 2-1/2 inches wide. Your ribs will be 1/4 inch thick, so you can get about 7 sticks out of each board assuming you lose 1/8 inch per cut. Each of those sticks will give you two ribs, so each board will give you 14 ribs. Allowing for breakage means that you will probably need three of those 5 foot boards to make all the ribs for your boat.
Step 2: Tools
Gloves for protecting your hands from hot wood
Saw for trimming the ribs
Clamps for holding the ribs in place on the boat
Step 3: Cutting Rib Blanks
Ribs bend most easily and with the least amount of breakage if you cut your blanks so they have vertical grain. To do that, start out with a plank that has flat grain. The slices you cut off the flat grained plank will have vertical grain.
Step 4: Soak the Rib Blanks in Water
Step 5: Cut Up the Rib Blanks
Step 6: Round the Edges of the Rib Blanks
Step 7: Mark the Bend Position
Step 8: Rib Shape
As you proceed toward the bow, the hull will get narrower and taller so that the ribs start becoming more arched in the center.
As you move toward the stern of the boat, the hull becomes flatter so the ribs tend to stay flat in the middle with the bends concentrated near the edges until the very end.
In general, the flatter the ribs are in the middle, the flatter the bottom of the kayak will be and the more stable it will feel.
Ribs that are more uniformly arched throughout will give you a more rounded hull that is less stable but slightly faster and livelier than a flat bottomed hull.
If you are building your first kayak or don't have much paddling experience go for the more flat hull.
Step 9: Rib Steaming
Step 10: Bend Ribs With Hot Water
Step 11: Rib Bending Strategy
Your next rib can be on either side of the first rib. Alternate back and forth until you have about 10 ribs in place, then put in all the ribs toward the stern. After that put in ribs toward the bow.
The reason for finishing one end of the boat and not hopping back and forth after you have the first ten ribs in is that the progression of shape in the front and the back of the boat is different and it is easier to get the transition of shape right if you stay on one end of the boat.
When you made the gunwales, you cut rib mortises to within 24 inches of the ends. You will probably find that gunwales at the last rib mortise are so close together that getting a tight enough bend in the middle of the rib is impossible without breaking it. So you can leave the last rib mortise on either end un-occupied.
After you pull a rib out of the steambox, you have a limited amount of time to bend it. Once it cools down, the rib begins to stiffen up. So you need to work fast. Once you have clamped the bent rib to the gunwales, you can still make adjustments to the shape, but the major bending should be done while the rib is right out of the steambox.
Ribs will remain pliable as long as they're wet. As they dry, they stiffen up and settle into their new bent shape.
Step 12: Rib Fairing Strategy
Step 13: Rib Trimming Strategy
Step 14: Bend Your First Rib.
Grab the rib on either side of the bend mark and bend it. Then bend the other side. Shove the rib between the gunwales and under the keelson and clamp it to the gunwales. Go to the end of the boat and check to see if the height of both bends is the same and symmetrical. If not, loosen the clamps and adjust the position of the rib to make it symmetrical.
In general, ribs want to arch up in the middle so that you need to push the legs of the ribs up at the sides to flatten out their shape in the middle.
When you are happy with the shape, move on to your next rib.
Step 15: Mark the Rib for Trimming
Also put a mark at the top of the rib at the keelson to indicate which side of the rib faces forward. After you trim the rib to length you will want to insert it with the right side facing forward.
Step 16: Trim the Rib
Rib mortises are half an inch deep. We add an eigth of an inch in length to make up for the fact that the rib ends will be farther apart when seated in their mortises.
Step 17: Taper the Rib Ends
Step 18: Insert the Rib in Its Mortises
Step 19: Bend the Rest of Your Ribs
Step 20: Put in Ribs Near the Ends of the Boat
Step 21: All the Ribs Are in Place
When we come back, you will be adding chine stringers and deck stringers to your kayak and doing a few other little odds and ends to complete the frame of your kayak.