Because of its high tensile or peel strength (it has a high “Shore A,” or hardness rating, and low elongation), polyurethane is considered to be both an adhesive or bonding agent as well as a bedding compound or sealant; in other words, it helps hold things together as well as forming a barrier to water. In fact, it cures to a tenacious rubbery consistency when exposed to water (and even when underwater) or atmospheric humidity. I’ve seen 8,000-pound ballast keels remain steadfastly stuck to fiberglass keel stubs after the keel fasteners were removed, solely by virtue of polyurethane’s adhesive qualities. Higher tensile-strength products should be used with extreme caution because nondestructive disassembly may be impossible. This semipermanent approach works well for gear that isn’t routinely removed — in which sealing as well as adhesion is welcomed — such as seacocks, struts, keels, hull-to-deck joints and so on. However, it can prove problematic if used on less permanent components like antennas, plastic ports or compasses.