Adding frames to the strongback

The next major step was setting up the frames on the strongback. I decided to start with frame B: it’s light, simple, and sits roughly in the middle of the structure, which makes it a good reference point for everything that follows.

All frames on the strongback

Looking back, there’s one thing I should have done earlier when building the frames: marking both the centerline and the waterline on each one. The centerline is relatively easy to establish after the fact, but the waterline can be tricky on some frames. Fortunately, I later found a reliable way to work around this using the laser level, which I’ll describe below.

Marking the center line

The yard owner kindly lent me a few wooden boards to use as vertical posts for holding the frames. My method for fixing these posts was systematic. First, I clamped the board in place and used a level to get it perfectly vertical. Then I pre-drilled and fastened a first screw. After removing the clamp, I rechecked the vertical alignment; the single screw allows just enough movement to fine-tune the position while providing enough friction to keep the board where you want it. Once satisfied, I pre-drilled and added three more screws to lock it in place.

Setting up a vertical post for frame B

With two vertical boards ready to hold a frame, I used leftover offcuts from the frame strips as small support blocks underneath the frame. I started with a reasonable guess for their height and clamped them in place, then rested the frame on top. Some frames—especially the lighter ones—had a tendency to tip forward at the top. A simple but very effective solution was to tie a rope around the upper part of the frame using a rolling hitch. This knot lets you easily tighten or loosen the rope while making adjustments, and it kept the frame safely under control.

Levelling and centering each frame turned out to be a lengthy and fairly delicate process. Before touching the frames themselves, I made sure the strongback was square. Using the vertical line from the laser level, I checked that all the center markings on the crossbeams were perfectly aligned. I then marked the waterline on the first set of vertical boards at 150 cm height, as specified in the CNC strongback plans.

Laser level - marks the central and water line

For each frame, the first task was to align its centerline with the vertical laser line. Once that was done, I adjusted the height by moving the clamped support blocks up or down. Initially, I tried marking the waterline directly on each frame, but I eventually found a more reliable approach. After placing a frame, it’s easy to hang a tape measure vertically and see where the laser line intersects it. By checking both the left and right sides and making small adjustments, you can bring the frame to the correct height with good accuracy.

Hang the tape measure to check the height of the frame

The final adjustments—those last few millimetres—are the hardest. What worked best for me was to pre-drill and fasten a first screw into each support block while it was still clamped. Once the clamp is removed, the block usually stays in place, but you can still rotate it slightly up or down to dial in the exact height. When everything looks right, a second screw locks it permanently.

Some frames were easier to set up than others, especially compared to the heavier ones, but progress was steady. Eventually, all the frames were standing on the strongback. This felt like another significant milestone: for the first time, the size and shape of the boat were clearly visible in three dimensions.

Before I can think about adding the stringers, there’s one final preparatory step left: building the stem to define where the bow ends. That, however, is a story for the next post.