It just so happens the captain's daughter (Edna Purviance - of course, she often played the leading lady in Charlie Chaplin films of this era) is in love with a tramp (Charlie - of course). The captain gets Charlie to shanghai him some crew... and then shanghais Charlie too.
So its a Charlie Chaplin slapstick farce at sea - causing various mayhem and eventually foiling the plan to blow up the ship. An enjoyable film, especially as there is some actual story to hang the action on.
