The strongback is simply a long straight beam to which you attach the building forms. It can be a length of 2" by 4" Deal, but as you need quite a long length and as most timber sold in hardware shops is seldom straight, for accuracy sake I built one from 3/2" MDF.
It is 14' 11"" long, as per the
book. I made a 1/4" rebate along
the edges of the wider sides and glued/screwed
the whole lot together. As the MDF I had
was 4' long, I had to plan that the longitudinal
joints ( I use butt joints ) were offset
from each other. Again, the book came
to the rescue with suggested layouts.It was amply stiff for building on, but a
little delicate ( when the forms were
) for one person to lift. It
I made three trestles, H-shaped, and lined these up lengthwise on some chipboard sheeting on the floor. I used corner brackets and screwed the legs of the trestles to the chipboard. This gave me a firm foundation. I cut out six U-shaped pieces of MDF, the U-shape being the size of the strongback, and screwed them to the tops of the trestles, aligning them along the way. This gave me a level foundation. On went the strongback, then I threaded the forms along it, spaced at 12" intervals. Then came the hard part, aligning the forms. This took ages, sighting along the marks and adjusting them on the strongback until they all lined up. I had drilled holes in each form with the intention of threading fishing line through them to aid lining up. This didn't work too well, I couldn't tell if the line was being pulled sideways by any of the forms. I tried shining a torch through the holes. The light was visible. However, I think aligning the forms using the marks is the best way to go.
I then attached the stem and stern forms. With both I had a slight problem, they didn't lie fairly with the tops of the adjacent forms. I rechecked the offsets but couldn't understand this. Eventually I decided that the difference wouldn't cause a problem so I used the chisel to adjust them. I don't think this was a big deal.
When all was done I could see the shape of the kayak.
Here I could have made things easier for myself. I had cut holes in the forms which were 4" x 2" to allow for adjusting the forms. In hindsight, I think I should have cut the holes a tightish fit for the strongback, as the strongback was accurately made. I think this would have made lining up accurately much easier.