I was thinking that it might be an "easy" intro project to just make box beams of fiberglass (and carbon) and replace the bulk of the trailer with lightweight construction, just reusing the complicated pieces (axle, bearing, hitch).

This got me to thinking about box beam construction. I have not been clear if the harryproa beams are all fiberglass/carbon or if they are sandwich construction as well. I have never seen any mention of core material for masts, so is coring used for box beams, and if so, why is that different than for a circular section.

I expect this is basic mechanical engineering, but I am ignorant, so it would be great if I could get a basic understanding.

How would I calculate the strength of a box beam, based on the dimensions, wall thickness and material, with and without a core?

- Gardner