Writer/Director Terry Jones is also the author of a children's novel called 'The Saga Of Erik the Viking', although the plot lines of the movie and the book have nothing more in common than the same-named titular characters.
Erik runs through waist-deep water to get on shore to get the Cloak Invisible. When he arrives in Aud's bedchamber minutes later, his pants are completely dry.
As the ship is flung a great distance by the dragon, some of the Vikings fall out. This wouldn't happen, since they're following the same parabolic trajectory as the ship.