Last year I painted the hull with Gelshield® 200 followed by an antifouling. When lifting the boat most of the antifouling had detached. What has happened?

Epoxies like Gelshield® 200 and Interprotect® cure to a very hard film, a film that at the right thickness will protect against water permeatation. Due to the fact that it hardens up so quickly, the overcoating times for an antifouling are very short. If you wait until next day to apply the antifouling, the epoxy will be so hard that the antifouling will not adhere strongly to it. The problem normally appears when exposed to water for a longer time and the paint will start to detach.