I am making a Kevlar canoe and have a question about flex and laminate failure. Most of the impact occurs between the bilge turns on each side, ie the bottom and up several inches. I would like the overall shape to be quite stiff and was planning on using a 1/4" core on the topsides. I was thinking of not coring the bottom to allow some give on impact, although the bottom must be stiff enough to prevent distortion from buoyancy effects. I have two questions:
Will the transition from cored to solid laminate present a zone of likely failure?
Is the difference between flex on impact and laminate failure with a solid Kevlar layup so narrow that it’s not worth trying to engineer?
All canoes that I see being built (recreational and race, up to olympic level) use a core throughout, probably to get the stiffness they want, for the given weight spec.
Most use 3mm core, which can be Coremat / Soric, Cork, Foam or honeycomb. (the last ones are rare, even the Olympic boats usually are foamsandwich.
The transition of a cored to non cored panel is always an issue, as the stiffer cored laminate acts as a hard point.
Also, for what I know of it, I would like to see a thicker core in the bottom, as that is a relatively large panel with little support, and the most (hydrostatic) force on it.