We bought a 1989 16’ Mad River Explorer today and I’m confused about the gunwales. They appear to be wood on the inside but plastic or vinyl “faux wood” on the exterior trim. Additionally the Royalex edge is completely exposed - you can see the foam core sandwiched between the vinyl sheeting sandwiched between the exterior and interior gunwales - and I don’t know if that matters or not. The decks are also a piece of Royalex with an exposed edge. I’m most familiar with boats that have vinyl gunwales that completely cover the top edge of the canoe so this design is a new for me.
Looks to me like the exterior wood gunwales and decks were probably replaced by a previous owner possibly due to wood rot. I think there is a good chance of cold cracks if the screws aren’t backed out. There is a good chance that the replacement gunwales are plastic decking or trim. I seem to remember that the exposed ABS and foam core can deteriorate when exposed to UV and absorb water in the foam core which can lead to delamination. Small holes and cracks can be filled with epoxy putty designed for ABS or a similar adhesive like G-flex epoxy. I have done skid plates of G-flex mixed with black carbon powder to protect exposed ABS core from UV.
It is fine to leave the sandwich exposed. Nothing will come of it.
My grandfather was part of the original team at Royal Rubber & Tire that developed Royalex and marketed it to boat makers. Royal wasn’t in the business of competing with boat makers, but they made several demo boats early on to show off the material’s capabilities. As part of the demonstration, they dropped a boat from the top of a building and showed how the hull would twist and the wood trim would break, but the hull was undamaged. They also showed that the hull would float from its own buoyancy. My family still has a canoe, a flat end canoe, two rowboats, and a speed boat from those days.
Our canoe and rowboat spent all summer for decades tied up at our dock and fully exposed. They are trimmed out with ash inwales and outwales and have the sandwich exposed all along their hulls, and they also have pieces screwed on the ends for caps.
In these boats’ 60+ years, the exposed sandwich has never delaminated or shown signs of deterioration, and water has never penetrated them that I can tell. The color of the hulls probably dulled from what they were new, but none of these boats have ever faded to any significant extent. I replaced the inwales and outwales on the canoe when I was in college (30+ years ago), after they were at least 30 years old, and the wood has held up just fine. We used to store them through the winter under our porch, and now we keep them in our unheated garage, and I would say that only the sun got to the wood, and it took several decades.
