In wooden ships, floor timber is the support below the flooring plank. As modern ships are not made of timber, the same concept is known by several names; bulkhead, transversal frame or side girder. This steel framing is usually made with lightening holes.[1][2] If floor timbers lay tight between the floor and the hull, bulkhead compartments are created.
In modern ships, the inside space at the bottom produced by transversal frames are called bilges in plural, singular for the external side or bilge.