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.
When Erik's ship arrives at Hy-Brasil, it has been damaged and is sinking. The Vikings are never shown to have repaired it, yet they are able to take it to sea against Halfdan the Black's attack.
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.