The popular polyurethane adhesive 5200 has competitors under different brands, but polyurethane is the most-reached-for goo in boatyards and factories when it’s time to mount cleats, through-hull fittings and synthetic teak products, and even join the hull to deck. No wonder. Polyurethane adhesive cures tough and flexible. It sticks to wood, metal, fiberglass and, if you let it cure long enough, your skin too. Fabrics have been repaired with it, and the best-built boats have pounds of it in various places. Its curing process is days long but, curiously, faster when in contact with water, making it ideal for through-hull fittings.