Caledonia Yawl – Chapter 2: Construction continues

We are getting into full swing on the construction of the boat. In the last few weeks we have made the station molds and set them up on the ladder frame.

Making the molds is an interesting operation. We take 3d nails and lay them along the station lines of the body plan. We then take a section of 1×6 pine and place it on top of the nails and give it a few good whacks with a mallet. This transfers the location of the 3d nails to the underside of the 1×6 pine. Using a batten, we draw a line connecting the indents, creating a fair curve representing the shape of the hull that station.

We then nail the 1×6 pine to a second piece of pine and cut both simultaneously on the bandsaw, This ensures the port and starboard sides of the mold are identical. The molds are usually made in several sections, so the process is repeated until the entire curve of all the stations are created. The sections of the mold are assembled into a whole, creating the shape of the hull at that station. A cross spall is added to each mold at the baseline. The location of this cross spall is critical, as it establishes the height of the mold on the ladder frame. This ensures the molds are all vertically aligned with each other.

Caledonia Yawl station molds

Caledonia Yawl station molds

We set up the ladder frame in the shop, making sure the rails are parallel, level and in the same plane as each other. The rails are spaced an appropriate distance apart based on the beam of the boat being constructed. To support the stems, cross members at the bow and stern are set at an angle. We transfer the location and angle of the stems from the lofting. We then stretch a string to mark the center line the length of the ladder frame.

Ladder Frame

Ladder Frame

Then we were ready to set up the molds. Using the lofting as a reference, we marked the locations of the molds on the rails. Then one by one we installed each mold aligning the center lines and ensuring they are level and plumb.

Station 1 mounted on the ladder frame

Station 1 mounted on the ladder frame

All the molds setup on the ladder frame

All the molds setup on the ladder frame

Station molds viewed from the stern

Station molds viewed from the stern

We decided to laminate the inner stems with 9 to 10 laminations of sapele. Using the same method with the 3d nails, we transfer the shape of the stems to two pieces of 2.7 mm door skin to make a pattern for each stem. We then trace the curve of the pattern on a piece of particle board. We glue and screw short sections of 2 x 4 every few inches along the curve. The laminations are bent around these blocks and clamps hold everything in place until the epoxy cures. Once well cured (about 24 hours) we plane the stems to thickness.

Stem laminations

Stem laminations (note keelson on top of the molds in the background)

In the meantime we’ve milled up the material for the keelson.  We have learned from experience to cut the centerboard slot in the keelson on the table saw before installing it on the ladder frame. For aesthetics, we beveled the top edge of the keelson and inside face of the stems. Then the keelson and stems are installed on the ladder frame to form the backbone. The outer face of the backbone is beveled to accept the planking. All of this setup is time consuming, but well worth it in terms of easing construction going forward, but more importantly, to have a pleasing shape to the hull.

Lining off the planking

Lining off the planking

While glue is curing we are working on other items. We draw the shape of the rudder on the lofting. This helps us determine the location of the rudder and the rudder hardware so we can get it on order.

We also draw the centerboard trunk on the lofting. We make a pattern for the centerboard and place it on the lofting to make sure it fits well and that there is adequate clearance as the board moves up and down in the trunk.

Centerboard and c/b trunk patterns

Centerboard and centerboard trunk patterns

Centerboard pattern

Using pattern to make sure centerboard will pivot in the trunk

We use the same 3d nail technique to make a pattern for the centerboard trunk. This is made from 9 mm okoume marine ply with sapele logs and spacers. This is glued in sections and set aside until ready for installation.

Centerboard trunk gluing up

Half of centerboard trunk gluing up

Once the backbone is set up and beveled we start making patterns for the strakes. We can hang a pair of strakes a day, so this seven strake boat will be planked in little over a week.

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