Building the strong back consists of two parts: making the strong back, the beam on which the forms are mounted; and making the support, which keeps the strong back aligned and solid during construction.
The support consists of 6 inverted T's each made of two layers of 3/4" G1S plywood sandwiching 3/4" Baltic birch in the base, for receiving threaded 1/4" inserts and plastic feet, and a gap at the top where an L will be mounted and height adjusted for receiving the strong back. The adjustment is necessary because the strong back varies in depth from 3", to 4" to 5" and back to 3" as it goes down the boat. As long as the support is rigid and close to being aligned, the fine-tune adjustments can be made with the L pieces as shown below.
The longitudinal and vertical position of the T's are held by 2x6's which are lag-bolted (not shown) and bolted thru with ready-rod.
Here I am fine-tuning the position of an L seat. The red dot is from my laser level to ensure that all the L's were vertically adjusted correctly. The string aligns all the L's down the length of the support. and the spirit level is used to make sure that the seat of the L is parallel with the ground. As each one was set in true position, I clamped it with a spring clamp, then screwed it twice from each side of the support.
Here is the completed support with the L's set as required to receive the strong back with the boat in the upright position.
Note that it is common to build kayaks making the hull first, therefore mounting the strong back upside-down initially. I have a reason to build the top decks first, which I will get into later when we get to that part.
Then, it's a matter of building up the beam portion of the strong back, and sliding the forms on at their 6" intervals. A trick is to rub floor wax generously on the beam to help ease the tight-fitting forms along. I know I broke a couple of forms in my first project. I didn't break any this time. Either I'm more patient now or perhaps just wiser. I'll credit the Baltic Birch.
So, after a 13-hour day, the forms are on the strong back and the whole affair is sitting on a rigid support. Note that the 26ft long boat is fitting diagonally across 2 bays of our carport. This was a great compromise because it left room for Rick to park his BMW motor bike, AND the entire length of my boat is under cover! (see pic below!)
This photo also shows my first boat hanging in the rafters, and the form for it up on a rack on the wall to the right. Hopefully I'll get "My Escape" into the water soon so I can row while the new boat is getting built.
Whew! Just fits! But, not finished the form yet. Each station has to be checked and secured, than the Shearline bracing goes on. Lots to do yet....