Of course, it will still pay to buy top quality solid hardwood, but in Africa, that should be available. I heard of a strip planked boat that rotted out within eight years, due to the use of poor quality red cedar. I wouldn't want to avoid the use of epoxy, it brings so many benefits with it, but it's certainly possible to avoid the use of plywood. Double diagonal and triple diagonal construction have long been known as ways to build a strong boat, and in fact, what you're doing is making plywood in situ rather than buying it in sheets.
Reuel Parker, in his book The New Cold-Molded Boatbuilding, talks about building the compound-curved bottoms of his boats with longitudinal tongue and groove planks, followed by double diagonal planks (though he then goes on to use plywood for the topsides and decks).