What determines the heights of decks above the main deck?

The heights of decks above the main deck are determined by the concept of "level," which reflects the vertical positioning of decks within the structure of the vessel. In naval terminology, levels correspond to different floors or decks, with the main deck being the reference point. By understanding levels, one can accurately identify the height and relative position of various decks in relation to the main deck.

Deck numbering is typically sequential and relates to the deck's order but does not provide information on the actual height above the main deck. Frame numbers are used for structural and engineering purposes and indicate the position of transverse frames within the hull but are not expressed in terms of height above the main deck. Bulkhead designations identify specific vertical partitions within the ship and do not convey vertical height measurements; they serve to indicate division of spaces rather than establish their vertical relationships. Therefore, level is the most relevant term when discussing the heights of decks in relation to the main deck.