The upper deck is the uppermost complete deck exposed to
weather and sea, which has permanent means of weathertight closing
of all openings in the weather part thereof, and below which all openings
in the sides of the ship are fitted with permanent means of watertight
closing. In a ship having a stepped upper deck, the lowest line of
the exposed deck and the continuation of that line parallel to the
upper part of the deck is taken as the upper deck.