The strength deck is the deck which forms the uppermost flange of the hull girder. The relative distance of this deck from the neutral axis contributes to the longitudinal strengthof the vessel. The deck needs to extend over a significant portion of the ships length to be effective as a longitudinal member; as such, the strength deck is generally the main deck (decks in the superstructure of ships, where the superstructure extends over much of the ship (i.e., cruise ships), are often strength decks).