46 C.F.R. § 69.103
As used in this subpart-
Between-deck means the space above the line of the tonnage deck and below the line of the deck next above.
Break means the space between the line of a deck and the upper portion of that deck, in cases where that deck is stepped and continued at a higher elevation.
Camber means the perpendicular rise or crown of a deck at the centerline of the vessel measured above the skin of the vessel at the vessel's sides.
Ceiling means the permanent planking or plating fitted directly on the inboard side of frames, floors, or double bottom and includes cargo battens and refrigeration insulation but does not include false ceiling which stands off from the framing.
Coaming means both the vertical plating around a hatch or skylight and the sill below an opening in a bulkhead.
Deckhouse means a structure that is on or above the uppermost complete deck and that does not extend from side to side of the vessel. The term includes cabin trunks and closed-in spaces over the holds of vessels.
Depth of frame means the perpendicular depth of a bottom frame and the athwart distance between the inboard and outboard faces of a side frame.
Double bottom means a space at the bottom of a vessel between the inner and outer bottom plating and used solely for water ballast.
Double bottom for water ballast means a space at the bottom of a vessel between the inner and outer bottom plating, used solely for water ballast.
Floor means a vertical plate or timber extending from bilge to bilge in the bottom of a vessel. In a wooden vessel, "floor" means the lowermost timber connecting the main frames at the keel when that timber extends the full depth of the frames to which it is fastened. In a double bottom, floors usually extend from the outer to the inner bottom.
Gross register tonnage is defined in § 69.107(a) .
Hatch means an opening in a deck through which cargo is laden or discharged.
Line of the normal frames means the imaginary horizontal line that connects the inboard faces of the smallest normal frames.
Line of the ordinary frames means the line of intersection of the imaginary surface or surfaces tangent to the inboard faces of the ordinary frames (or the inside of the vessel's skin, if there are no ordinary frames), and the imaginary plane running transversely through the vessel at the tonnage station of interest.
Line of tonnage deck means the line determined under § 69.109(e) .
Line of uppermost complete deck means the line determined under § 69.111(b) .
Net register tonnage is defined in § 69.107(b) .
Normal frame means a frame, regardless of size, used to stiffen a structure.
Ordinary frame means a primary side or bottom frame or floor used for strengthening the hull.
Registered breadth is defined in § 69.53 .
Registered depth means "molded depth" as defined in § 69.53 .
Registered length is defined in § 69.53 .
Shelter deck means the uppermost deck that would have qualified as the uppermost complete deck had it not been fitted with a middle line opening.
Step means a cutoff in a deck or in the bottom, top, or sides of a space resulting in varying heights of a deck or varying heights or widths of a space.
Superstructure means all permanently closed-in structures, including all portable enclosed spaces, on or above the line of the uppermost complete deck or, if the vessel has a shelter deck, on or above the line of the shelter deck. Examples of superstructure spaces include forecastles, bridges, poops, deckhouses, breaks, portable tanks, and modular quarters units.
Tonnage deck is defined in § 69.109(c) .
Tonnage interval means the longitudinal distance between transverse sections of a vessel's under-deck, between-deck, or superstructure when divided into an even number of equal parts for purposes of volume integration.
Tonnage length is defined in § 69.109(f) .
Tonnage station means the longitudinal location of each transverse section where breadth and depth measurements are taken when calculating under-deck volumes under this subpart. Tonnage stations are numbered consecutively from fore to aft, beginning with the number one.
Uppermost complete deck is defined in § 69.108 .
Zone of influence method means a Simpson's first rule integration method for determining volumes of under-deck spaces that limits the sectional areas associated with these spaces to the sectional areas at adjacent under-deck tonnage stations, depending on their proximity to those stations. For stations for which the under-deck sectional areas are multiplied by four, the zone of influence extends two-thirds of a tonnage interval on either side of the under-deck station, and for the remaining stations, the zone of influence extends one-third of a tonnage interval on either side of the station.
46 C.F.R. §69.103