A ramp of wooden stairs up to a 2 floorboard long platform above the deck, preferably using a longship. Push them onto the deck or place food at the end of the platform, then destroy it once they are above the deck. Go slow, gradually building up speed, because too much acceleration and they can slide across the deck and debark. Stay far enough away from coastlines so they will not agro any enemies, but not so far that you are in Sea Serpent territory, as they will jump ship to attack enemies just like wolves will do.