Building a Cedar Strip Kayak: The Details: Stems and Sheer Clamp

The stems on a strip built kayak are made the same way as the stems on a strip built canoe. The stems are ¼ strips of wood which are steamed, shaped and glued together with thickened epoxy. They are made up of an inner stem (4 pieces of cedar or other softwood) and outer stem(2 pieces of hardwood, I used Cherry).The inner stems are where the end of the hull strips are stapled and glued. The outer stems are attached after the hull is stripped.

Steaming the stems

The stem strips are cut long enough to extend past the ends of the stem forms. They are then soaked in water overnight before steaming. I made a steamer out of a length of 6” pvc pipe and its ends plugged the ends with a circular block of wood. One of the plugs had a hole cut into it for steam to enter. The steam came from a large coffee pot with a piece of copper tubing replacing the glass bubbler in the lid. It was then set on a camp stove with the copper pipe through the hole in the pvc pipe plug. The strips were placed in the pvc pipe and it was hung from the rafters in my garage while the strips steamed.

If you don’t steam the stems long enough they will crack if you try to bend them sharply. When they are ready the side of the pvc pipe will start to become soft, and lots of steam will escape from a small hole that you drilled in near the top of the pipe.

Clamping

The stem strips are then clamped to the stem forms and allowed to cool and dry for a few days. Be sure the outer hardwood stems are the last ones placed on the stem forms. Once they have dried, it is time to glue them together. First the edges of the stem forms are covered with plastic packing tape to prevent the stems from becoming glued to the forms. Epoxy thickened with sanding duct is used for glue. Small batches can be mixed by filling a plastic cup with water in the correct ratio for resin and hardener then marking lines on the side of the cup with permanent marker. I used epoxy with a 3:1 resin/hardener ration so I filled the cup with 6 tablespoons of water, marked the line, then 2 tablespoons more of water and marked another line.

Before the epoxy is thickened with wood sanding dust, the strips should be coated with un-thickened epoxy for better glue joint. An ample amount of thickened epoxy is then place on the face of the adjoining strips except the between the inner softwood stems and outer hardwood stems. More plastic packing tape is place on this face to keep the stems from being glued together.

The bundle of glued strips is firmly clamp to the stem forms but not so much that all the glue is forced out. The epoxy is then allowed to harden for a few days.

Attaching the stems

Once the epoxy has hardened the stems are removed from the forms and they are re-attached to the build table. The inner stems are then cut to fit the stem form so that the inside end butts against the first hull form. A screw through the hull form hold the stem in place on one end and a clamp holds it in place on the other. The stems are then marked with a center line and another line 1/8” one each side of the center line. Using a plane, sure form plane, file or spoke shave the stems are shaped by removing wood down to the outside lines, so that the hull strips will fit flat against them.

Sheer clamp

The sheer clamp is what is used to attach the deck to the bottom of the hull. A 7/8” x ¾” strip of wood that runs the length of the hull is attached at the notches cut in each form. I cut them from a 10 ft. pine 2x4 then was scarf joined the pieces to get the length. Here was one of my first mistakes. When the notches for the sheer clamp were marked on the forms, they were over sized. I had to make adjustments using spacers when attaching the sheer clamp. The sheer clamp is attached to the forms with screws through the downward facing side of the clamp into the forms. Clearance holes in the clamp and pilot holes in the forms should be drilled to avoid cracking.

The slots in the stems where the sheer clamp enters should be covered with packing tape. The ends of the sheer clamps are cut at an angle so that they can be joined together with a flat surface when clamped. Thickened epoxy is used to glue the ends of the sheer clamps together and a screw coated with wax holds them together while the epoxy hardens.

Once the sheer clamp was in place, I made adjustments by planning and using duct tape on the edge of the forms to make sure the sheer clamp lined up with the form edges.

The edges of the forms and the sheer clamps were then covered with plastic packing tape. The first strip was stapled to the sheer clamp allow it to extend below the bottom edge of the clamp about 1/8”.

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