one and typically many generally vertical walls 26 also termed 34 bulkheads 34 extending between the decks 24 the horizontal decks 24 and the vertical walls 26 divide the interior of the ship into many compartments 28 fig2 shows a typical prior construction three decks 24a 24b and 24c are shown with walls 26a extending between the decks the walls 26a are all structural walls made of steel and serving to bear a portion of the overlying loads fig3 5 illustrate a construction according to the present invention referring to fig3 the ship 20 includes the same decks 24a 24b and 24c some structural walls 26a extend between the decks defining watertight compartments 28a additionally some non structural wall segments 26b extend between the decks further dividing the watertight compartments 28a into non watertight compartments 28b in fig2 and 3 a structural vertical wall 26a is denoted by double lines and a non structural vertical wall segment 26b is denoted by a single line the structure according to the present invention may be conveniently described as a skeleton 29 with non structural wall segments attached to the skeleton fig4 depicts the skeleton 29 which is preferably made of steel with all of the elements of fig4 rigidly welded to each other the skeleton 29 includes the hull 22 one or more horizontal decks 24 and one.