: Someone help me understand what appears to be
: some conflicts about internal strongbacks here.

Because one builds the vessel from the forms, continuous form alignment during the building process is of some fundamental importance. Form continuity during the early part of the process is provided by a rigid strongback or strongback support system. However fairly quickly, strips are attached (maybe even temporarily) around the forms causing the whole form and strongback assembly to be a fairly rigid assemblage itself. Initial form alignment, on the other hand, is often provided from an attempted straight and ‘level’ strongback but also can be provided by aligning the forms themselves independent of the strongback - therebye allowing the strongback to have building deviancies or twists as its shape can be actually irrelevant to defining the vessel shape (as long as it is a stiff and stable spine or platform). (ie why care about the beam alignment, if one really cares about form alignment?)

Many kayaks have been built using 2x4’s however because of their variable flexibility from support conditions or humidity changes, it behooves the builder to have good support and get to an assemblage stage fairly rapidly while checking form (not strongback) alignment along the way. Or the next best thing is to use a more rigid strongback (whether internal or external) from the start.

Well constructed plywood or steel or aluminum beams will provide that stiffness required but their size needs to match the size of the vessel being constructed.

Going back in the archives you will see internal aluminum box beams, extruded steel boxbeams, steel stud boxbeams, trussjoist beams, plywood boxbeams of many sizes as well as external boxbeams as well.

(incidentally, nick’s videos show (straight and untwisted) aluminum 2x4 boxbeams threaded with accurately beamcut forms that therefore self-align to the straight beam)

Summing up
- rigidity of the beam (assembly if necessary) whether internal or external is fundamental.
- Straightness and twistyness of the beam is unimportant unless one uses the beam for alignment.
- Alignment of the forms is fundamental.