Polyurethane sealer. Tack tree in 48 hours. Cures in 5-7 days with no shrinkage. Extremely strong above or below the waterline. Stays flexible. Bonds and seals fiberglass deck to fiberglass hull, wood to fiberglass. Easy to apply with a manual caulking gun. Workable up to 4 hours after application. Won't sag or flow in vertical or horizontal seams.