This subpart prescribes the procedures for measuring a vessel under the Standard Regulatory Measurement System described in 46 U.S.C. 14512.

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.

Applications for measurement services under this subpart must include the following information and plans:

(a) Type of vessel.

(b) Vessel's name and official number (if assigned).

(c) Builder's name and the vessel hull number assigned by the builder.

(d) Place built and delivery date (or scheduled delivery date).

(e) Date keel was laid.

(f) Overall length, breadth, and depth of vessel.

(g) Lines plan.

(h) Booklet of offsets.

(i) Capacity plans for tanks

(j) Construction plans showing measurements and scantlings of hull and superstructure.

(k) Tonnage drawing showing tonnage length in profile and tonnage sections.

(l) Arrangement plans.

(a) The vessel's gross register tonnage is the sum of the following tonnages, less the tonnages of certain spaces exempt under § 69.117:

(1) Under-deck tonnage (§ 69.109).

(2) Between-deck tonnage (§ 69.111).

(3) Superstructure tonnage (§ 69.113).

(4) Excess hatchway tonnage (§ 69.115(c)).

(5) Tonnage of framed-in propelling machinery spaces included in calculating gross tonnage (§ 69.121(d)(1)).

(b) The vessel's net register tonnage is the gross register tonnage less deductions under §§ 69.119 and 69.121.

(c) The authorized measurement organization must issue a U.S. Tonnage Certificate as evidence of a vessel's measurement under this subpart, which must also indicate the vessel's measurement under the Convention Measurement System in subpart B of this part, if applicable. There is no requirement to maintain the U.S. Tonnage Certificate on board the vessel.

(a) Defined. “Uppermost complete deck” means the uppermost deck which extends from stem to stern and from side to side at all points of its length and is bound by the vessel's hull.

(b) Restrictions. The uppermost complete deck must not:

(1) Extend above any space exempted as open space under paragraph (d) of § 69.117;

(2) Extend below the design waterline, except in the case of vessels such as submersibles, where the entire uppermost complete deck is submerged during normal operations; or

(3) Rest directly on consecutive or alternating ordinary bottom frames or floors for a distance of over one-half of the tonnage length.

(c) Deck discontinuities. Decking athwartships of the following deck discontinuities is not considered to be part of the uppermost complete deck:

(1) Through-deck openings that are not protected from the sea and the weather, such as would be provided by hatch covers or a surrounding superstructure that encloses the opening and whose area is more than 10 percent of the total deck area from stem to stern as viewed from above.

(2) Middle line openings conforming to the requirements of § 69.117(e)(2).

(3) Deck recesses that are not through-hull for which the depth of the deck recess at its deepest point is more than five feet below adjacent portions of the deck, and whose area (as viewed from above) is more than 10 percent of the total deck area from stem to stern, as viewed from above.

(4) Notches bounded by a deck below that wrap around from the ends to the sides of the vessel for which the depth at the deepest point is more than five feet below adjacent portions of the deck, the area is more than one percent of the total deck area from stem to stern as viewed from above, the length of the notch in the direction of the vessel's longitudinal axis exceeds 10 feet at any point across its width, and the width of the notch in the direction of the vessel's longitudinal axis exceeds two feet at any point along its length.

(a) Defined. “Under-deck tonnage” means the tonnage of the space below the line of the tonnage deck, as that volume is calculated under this section.

(b) Method of calculating tonnage. Under-deck tonnage is calculated by applying Simpson's first rule using the tonnage length and the areas of the transverse sections prescribed by this section.

(c) Identifying the tonnage deck. In vessels with two or less enumerated decks, the tonnage deck is the uppermost complete deck. In vessels with more than two enumerated decks, the tonnage deck is the second enumerated deck from the keel as determined in paragraph (d) of this section.

(d) Enumerating the decks to identify the second deck from the keel. The uppermost complete deck is an enumerated deck. Decks below the uppermost complete deck that extend from stem to stern and side to side at all points along their lengths are also enumerated, provided they are not disqualified by either of the following deck discontinuities:

(1) A through-deck opening that is not fitted with a cover (or equivalent) and whose area is more than 10 percent of the total deck area, as viewed from above.

(2) A deck recess that is not through-hull for which the depth at its deepest point is more than five feet below adjacent portions of the deck and whose area as viewed from above is more than 10 percent of the total deck area from stem to stern, as viewed from above.

(e) Identifying the line of the tonnage deck. (1) If the tonnage deck runs in a continuous line from stem to stern, the line of the tonnage deck is the longitudinal line at the underside of the tonnage deck.

(2) If the tonnage deck is stepped, the line of the tonnage deck is the longitudinal line of the underside of the lowest portion of that deck parallel with the upper portions of that deck. Steps that do not extend from side to side or are less than three feet in length are ignored when establishing the line of the tonnage deck. (See § 69.123, figures 1 and 2.) Spaces between the line of the tonnage deck and the higher portions of that deck are not included in under-deck tonnage.

(f) Tonnage length. (1) “Tonnage length” means the length of a horizontal straight line measured at the centerline of the vessel from the point forward where the line of the tonnage deck intersects the line of the inboard faces of the ordinary side frames to the point aft where the line of the tonnage deck intersects the inboard face of the ordinary transom frames or cant frames. (See § 69.123, figure 3.)

(2) For a vessel having a headblock or square end with framing which extends from the tonnage deck to the bottom of the vessel, the tonnage length terminates on the inboard face of the headblock or ordinary end frames. (See § 69.123, figure 4.)

(3) For a vessel having a square bow or stern and tonnage deck with camber, the effect of the camber on the tonnage length must be considered. The tonnage length must be measured below the tonnage deck at a distance equal to one-third of round camber and one-half of straight pitch camber.

(4) The forward and after termini of the tonnage length must be a distance of no more than eight and one-half feet from the associated inboard surface of the skin of the hull at the bow and stern as measured at the centerline of the vessel, and the after terminus must not be forward of the centerline of the rudderstock.

(g) Division of vessel into transverse sections. (1) Except as under paragraph (m)(1)(iii) of this section, the tonnage length is divided into an even number of equal parts as indicated in the following table:

(2) Transverse sections are cut at each end of the tonnage length and at each point of division of the tonnage length, whose location is referred to as a tonnage station, and assigned sequential tonnage station numbers, beginning at the stem. Intervals and one-third intervals between the points of division are measured to the nearest thousandth of a foot. (See § 69.123 figures 5 and 6.)

(h) Depths of transverse sections. (1) Transverse section depths are measured at each point of division of the tonnage length at the centerline of the vessel from a point below the line of the tonnage deck equal to one-third of the camber or to one-half of the pitch of the beam down to the upper side of the ordinary frames, floors, longitudinals, or tank top of a double bottom for water ballast, as the case may be.

(2) When a depth falls at a point where the tank top of a double bottom for water ballast has a straight fall from centerline to the wings, the depth terminates at one-half of the height of fall. (See § 69.123 figure 8.)

(3) When a depth falls at a point where the tank top of a double bottom for water ballast rises from the centerline to the wings, the depth terminates at one-half the dead rise. (See § 69.123, figure 9.)

(4) The depth at the midpoint of the tonnage length or, when a vessel is measured in parts, the depth at the midpoint of each part determines the number of equal parts into which each depth is divided, as follows:

(i) If the midpoint depth is 16 feet or less, each depth is divided into four equal parts. If the midpoint depth exceeds 16 feet, each depth is divided into six equal parts. (See § 69.123, figure 7.)

(ii) The interval between the points of division of a depth and one-third intervals are carried to the nearest hundredth of a foot.

(i) Breadths of transverse sections. (1) Transverse section breadths are measured horizontally at each point of division of each depth and also at the upper and lower points of each depth. Breadths are measured to the inboard face of the ordinary frames or to the line of the ordinary frames. Breadths are measured parallel to each other and at right angle to the vessel's centerline. (See § 69.123, figure 7.)

(2) Upper breadths are not reduced by measuring to deck-beam brackets. In cases of camber when an upper breadth passes through the deck (see § 69.123, figure 7), the breadth is measured to the line of the side frames at the under side of the deck projected vertically up to the height of the upper breadth.

(3) Bottom breadths are measured only as far as the flat of the floor extends. (See § 69.123, figures 7 and 10.) When bottom frames rise immediately from the flat keel, bottom breadths are equal to the breadth of the flat keel. Where there is no double bottom for water ballast and where there is dead rise of the bottom out to the sides of the vessel, bottom breadths are equal to the part of the bottom plating not affected by dead rise.

(4) Bottom breadths falling in way of a double bottom, the top of which rises or falls from centerline to the wings, are measured between the inboard faces of the frame brackets which connect the double bottom with the frames. (See § 69.123, figures 8 and 9.)

(j) Measuring spaces having ceiling. The maximum allowance for terminating measurements on ceiling is three inches on the bottom frames or tank top and three inches on each side frame. When ceiling is less than three inches thick, only the actual thickness is allowed. When ceiling is fitted on a platform directly above the bottom frames, depths are measured down through the platform to the upper side of the frames and the allowable ceiling on the platform is then deducted.

(k) Area of transverse sections. (1) A transverse section at an end of the tonnage length may not yield area, except in vessels (such as barges) with an upright bow or stern.

(2) The breadths of each transverse section are numbered from above, the upper being “1”, the second down being “2”, and so on to the lowest.

(3) Multiply the even numbered breadths by four and the odd numbered breadths by two, except for the first and last breadths, which are multiplied by one.

(4) Add together the products from paragraph (k)(3) of this section.

(5) Multiply the sum from paragraph (k)(4) of this section by one-third of the interval between the breadths. The product is the area of the transverse section.

(l) Tonnage. (1) Number the transverse sections successively “1”, “2”, and so forth, beginning at the bow.

(2) Multiply the area of the even numbered sections by four and the area of the odd numbered sections by two, except the first and last sections, which are multiplied by one.

(3) Add together the products from paragraph (l)(2) of this section and multiply the sum by one-third of the interval between the sections. The product is the volume under-deck.

(4) The volume under-deck is divided by 100 and is, subject to exemptions, the under-deck tonnage.

(m) Steps in double bottom for water ballast. (1) The tonnage length of a vessel having a step exceeding six inches in height in its double bottom for water ballast is divided into longitudinal parts at the step. Each part is subdivided as follows to determine the number of transverse sections:

(i) Parts 20 feet or under in length are divided into two equal parts.

(ii) Parts over 20 feet and under 40 feet in length are divided into four equal parts.

(iii) Parts 40 feet or over are divided as provided in paragraph (g)(1) of this section.

(2) The tonnage of each part is calculated separately. The sum of the tonnages of the parts is the under-deck tonnage.

(n) Spaces open to the sea. In calculating the tonnage of spaces below the uppermost complete deck, subtract from each breadth measurement the portion of that measurement that spans a space, or a portion thereof, that is open to the sea.

(o) Open vessels. (1) An open vessel is a vessel without an uppermost complete deck.

(2) The line of the tonnage deck for an open vessel is the upper edge of the upper strake. Depths of transverse sections are taken from this line.

(3) Any vessel, other than one having a mechanically refrigerated hold, that is not an open vessel and that has a tonnage length of less than 50 feet is measured as an open vessel, if the distance between the line of its tonnage deck and the upper edge of the upper strake is more than one-sixth of the midship depth. “Midship depth” means the depth measured from the line of the upper edge of the upper strake to the point in the bottom used for measuring tonnage depths.

(p) General requirements on ordinary frames—(1) Construction. An ordinary frame must not be penetrated by an intersecting frame used to strengthen the vessel's hull, except in a vessel of wooden construction. Ordinary frames must be of the same material, or have the same material properties, as the adjacent hull, and attach to the adjacent hull to at least the same extent as adjacent ordinary and normal frames. If comprised of different elements, the elements must be joined to each other to the same extent that the frame is joined to the hull. The frame, or portions thereof, not meeting these requirements must be treated as if not there when establishing the line of the ordinary frames.

(2) Frame spacing and extension. Ordinary frames used to establish the line of the ordinary frames must be spaced on centers that are a maximum of four feet apart. These frames must extend for a length of at least one tonnage interval that begins at, ends at, or crosses the associated tonnage station. For a longitudinally-framed vessel, the frames must begin and end at a transverse ordinary frame or at the vessel's hull.

(3) Different sized framing. When an ordinary frame has a different depth of frame than an adjacent ordinary frame, the line of the ordinary frames is established using the set of alternating frames that yields the smallest sectional area at the associated tonnage station, with the sectional area based on the frame with the smallest depth of frame in the chosen alternating set.

(4) Frame openings. If an opening in an ordinary frame is oversized, or is penetrated by a frame other than an ordinary frame, the line of the ordinary frames is established as if the frame material above and inboard of the opening is not there. Similarly, frame material separating adjacent openings that are within the longest linear dimension of either opening must be treated as if not there when establishing the line of the ordinary frames. An opening is oversized if the opening is:

(i) Circular in shape with a diameter exceeding 18 inches;

(ii) Oval in shape of a size greater than 15 × 23 inches (i.e., either the minor axis exceeds 15 inches or the major axis exceeds 23 inches, and the oval's area exceeds 255 square inches (345 square inches in a fuel tank)); or

(iii) Any shape other than circular or oval, whose area exceeds 255 square inches (345 square inches in a fuel tank).

(5) Asymmetrical framing. Where ordinary frames are configured such that the line of the ordinary frames would be asymmetrical about the centerline of the vessel, breadth measurements are determined by taking half-breadths on the side of the vessel that yields the greatest sectional area at the associated tonnage station, and multiplying those half-breadths by a factor of two to yield the full breadths.

(a) Defined. “Between-deck tonnage” means the tonnage of the space above the line of the tonnage deck and below the line of the uppermost complete deck.

(b) Identifying the line of the uppermost complete deck. (1) If the uppermost complete deck runs in a continuous line from stem to stern, the line of the uppermost complete deck is the longitudinal line of the underside of the uppermost complete deck.

(2) If the uppermost complete deck is stepped, the line of the uppermost complete deck is the longitudinal line of the underside of the lowest portion of that deck parallel with the upper portions of that deck. Steps that do not extend from side to side or are less than three feet in length are ignored when establishing the line of the uppermost complete deck. Spaces between the line of the uppermost complete deck and the higher portions of the deck are included in superstructure tonnage.

(c) Method for calculating tonnage. The tonnage of each level of the between-deck space is calculated separately, as follows:

(1) The length of each level is measured at the mid-height between the line of the deck above and the line of the deck below. Measure from the point forward where the continuation of the line of the normal frames intersects the center line of the vessel aft to the forward face of the normal transom framing.

(2) Divide the length under paragraph (c)(1) of this section into the same number of equal parts into which the tonnage length is divided under § 69.109(g)(1).

(3) Measure at mid-height the inside breadth of the space to the line of the normal frames at each end and at each point of division of the length. Number the breadths successively “1”, “2”, and so forth beginning at the bow.

(4) Multiply the even numbered breadths by four and the odd numbered breadths by two, except the first and last, which are multiplied by one.

(5) Add together the products under paragraph (c)(4) of this section and multiply the sum by one-third of the interval between the points at which the breadths are taken. The product is the square foot area of the space at mid-height.

(6) Multiply the area of the space at mid-height by the average of the heights taken each point of division of the space. The product divided by 100 is the tonnage of that space.

(7) The between-deck tonnage is the sum of the tonnage of each level within the between-deck space.

(a) Defined. “Superstructure tonnage” means the tonnage of all superstructure spaces.

(b) Method of calculating tonnage. The tonnage of all structures on each level on or above the uppermost complete deck (or shelter deck, if applicable) is calculated separately as follows:

(1) Measure the length of each structure along its centerline at mid-height to the line of the normal frames. (See § 69.123, figure 11.)

(2) Divide the length under paragraph (b)(1) of this section into an even number of equal parts most nearly equal to those into which the tonnage length is divided under § 69.109.

(3) Measure at mid-height the inside breadth to the line of the normal frames at each end and at each point of division of the length. Number the breadths successively “1”, “2”, and so forth, beginning at the extreme forward end of the structure. If an end of the structure is in the form of a continuous arc or curve, the breadth at that end is one-half the nearest breadth. If an end is in the form of an arc or curve having a decided flat, the breadth at the end is two-thirds of the nearest breadth.

(4) Multiply the even numbered breadths by four and the odd numbered by two, except the first and last breadth, which are multiplied by one.

(5) Add together the products under paragraph (b)(4) of this section and multiply the sum by one-third of the interval between the points at which the breadths are taken. The product is the square foot area of the structure at mid-height.

(6) Multiply this area by the average of the heights taken at each point of division of the structure between its decks or the line of its decks. The product divided by 100 is the tonnage of that structure.

(c) A structure having steps in its deck or side must be measured in parts.

(d) The superstructure tonnage is the sum of tonnages of each level above the line of the uppermost complete deck (or shelter deck, if applicable).

(e) When a structure is located over a cut-away portion of the tonnage deck, the structure's height is measured from the under side of its overhead deck to the line of the tonnage deck. If the tonnage deck has no camber, allow for camber in the overhead deck.

(f) For structures of a standard geometric shape, a simple geometric formula that yields an accurate volume may be used. All measurements are terminated at the line of the normal frames.

(a) Hatchways that are above the tonnage deck and are either open to the weather or within open structures are measured to determine excess hatchway tonnage. Hatchways that are in between-deck spaces, on decks within closed-in structures, or on open structures are not measured.

(b) The tonnage of a hatchway is its length times breadth times mean depth divided by 100. Mean depth is measured from the under side of the hatch cover to the top of the deck beam.

(c) From the sum of the tonnage of the hatchways under this section, subtract one-half of one percent of the vessel's gross register tonnage exclusive of the hatchway tonnage. The remainder is added as excess hatchway tonnage in calculating the gross register tonnage.

(a) Purpose. This section lists spaces which are exempt from inclusion in tonnage.

(b) Spaces on or above the line of the uppermost complete deck. The following spaces or portions of spaces on or above the line of the uppermost complete deck are exempt if the spaces or portions are reasonable in extent and adapted and used exclusively for the purpose indicated:

(1) Spaces for anchor gear, including capstan, windlass, and chain locker, are exempt.

(2) Companions and booby-hatches protecting stairways or ladderways leading to spaces below are exempt, whether or not the spaces below are exempt.

(3) Galley or other spaces fitted with a range or oven for cooking food to be consumed on board the vessel are exempt.

(4) Spaces designed to provide light or air to propelling machinery are exempt, as follows:

(i) When propelling machinery is located entirely on or above the line of the uppermost complete deck, the entire propelling machinery space and all fuel bunker spaces that are also located above that line are exempt as light or air spaces. (See exception in § 69.121(d)(1) for framed-in spaces.)

(ii) When part of the propelling machinery projects above the line of the uppermost complete deck into a space used exclusively to provide light or air to the propelling machinery, the entire space is exempt as light or air space. When any portion of this space is used for purposes other than providing light or air, only the portion of the space used for light or air, the space occupied by the propelling machinery itself, and a propelling machinery working space allowance under § 69.121 limited to two feet, if available, on each side of the propelling machinery are exempt.

(iii) Any part of an escape shaft, or a companion sheltering an escape shaft, above the line of the uppermost complete deck is exempt as light or air space.

(iv) Space that would otherwise be exempt as a light or air space is not exempt when propelling machinery is boxed-in and does not extend above the line of the uppermost complete deck. Any portion of the boxed-in space above the line of the uppermost complete deck is exempt.

(5) Skylights affording light or air to a space below, other than to propelling machinery spaces. Space immediately below the line of the deck on which a skylight is located is exempt only when there is an opening in the next lower deck directly below the skylight to permit light or air to an even lower deck.

(6) Machinery spaces, other than for propelling machinery under § 169.121.

(7) Spaces for steering gear.

(8) Water closet spaces that are fitted with at least a toilet and are intended for use by more than one person.

(9) The space in a wheelhouse necessary for controlling the vessel.

(c) Passenger spaces. (1) As used in this section, the term “passenger” includes officers and enlisted men on military vessels who are not assigned ship's duties and not entered on the ship's articles.

(2) As used in this section, “passenger space” means a space reserved exclusively for the use of passengers and includes, but is not limited to, berthing areas, staterooms, bathrooms, toilets, libraries, writing rooms, lounges, dining rooms, saloons, smoking rooms, and recreational rooms. The space need not be part of or adjacent to a berthing area to be considered a passenger space. Spaces used by both passengers and crew members (e.g., first aid stations), or used for passenger support but not accessible to passengers at all times (e.g., vaults on a gaming vessel) cannot be exempted as passenger space.

(3) A passenger space located on, or above the first deck above the uppermost complete deck is exempt from tonnage. To qualify as the first deck above the uppermost complete deck, the deck must be at least six inches above the uppermost complete deck at all points along its length.

(d) Open structures. (1) Structures that are located on or above the line of the uppermost complete deck that are under cover (sheltered), but open to the weather are exempt from tonnage as open space. The following additional requirements apply:

(i) If a structure is divided into compartments, only those compartments which are open to the weather are exempt from tonnage under the provisions of this section.

(ii) Open space cannot progress vertically through openings in a deck within the structure.

(iii) A space that is outside a structure's boundary bulkhead as defined in § 69.53 is considered open to the weather provided the space is eligible to be treated as an excluded space under the provisions of § 69.61, regardless of whether or not the space is fitted with means designed for securing cargo or stores.

(2) A structure is considered open to the weather when an exterior end bulkhead of the structure is open and, except as provided in paragraphs (d)(4), (5), and (6) of this section, is not fitted with any means of closing. To be considered open to the weather, the end bulkhead must not have a coaming height of more than two feet in way of any required opening nor any permanent obstruction within two and one-half feet of the opening, it must be fitted with a deck or platform that is a minimum of two and one-half feet wide on the exterior side of the opening, and it must have one of the following:

(i) Two openings, each at least three feet wide and at least four feet high in the clear, one on each side of the centerline of the structure. If the openings lead to two separate interior compartments, there must be circulation of open space between the two compartments via a single such opening, or series of such openings, in the intermediate bulkhead(s).

(ii) One opening at least four feet wide and at least five feet high in the clear.

(iii) One opening at least 20 square feet in the clear with a breadth in excess of four feet and a height of not less than three feet.

(3) A compartment within an open structure is considered open to the weather only when an interior bulkhead of that compartment has an opening or openings that meet the requirements for end bulkheads under paragraphs (d)(2)(i) and (iii) of this section. Other compartments within the structure are not considered open to the weather. The following additional requirements apply:

(i) For the interior compartment to be considered open to the weather, any compartment or series of compartments from which the open space progresses must have an opening or openings meeting the requirements for end bulkhead openings, except that the opening(s) need not be located in the forward or after end of the compartment.

(ii) Open space may not progress from a space that is open under the provisions of paragraph (d)(1)(iii) of this section unless the space may also be considered open under another provision of this section.

(4) An interior or exterior opening that is temporarily closed by shifting boards dropped into channel sections at the sides of the opening is considered open to the weather if battening, caulking, or gaskets of any material are not used.

(5) An interior or exterior opening that is temporarily closed by cover plates or boards held in place only by hook bolts (see § 69.123, Figure 12) is considered open to the weather—

(i) If hook bolts used to secure cover plates or boards are spaced at least one foot apart and hook over a stiffener installed around the perimeter of the opening;

(ii) If the cover plates or boards fit tightly against the weather side of the bulkhead; and

(iii) If battening, caulking, or gaskets of any material are not used.

(6) An interior or exterior opening that is temporarily closed by cover plates or boards held in place only by bolts and crosspieces is considered open to the weather—

(i) If the bolts are not installed through the bulkhead;

(ii) If the bolts and crosspieces are not held in place by cleats or other attachments to or through the bulkhead;

(iii) If the cover plates or boards fit tightly against the weather side of the bulkhead; and

(iv) If battening, caulking, or gaskets of any material are not used.

(7) Notwithstanding the opening size requirements of paragraph (d)(2) of this section, a structure with its aft end entirely open from the under side of its overhead stiffeners down to the deck, to the line of the deck, or to a coaming not exceeding three inches in height and open athwartship between the inboard faces of the side stiffeners is considered open to the weather. The opening may be covered by a wire mesh screen or temporarily closed by canvas secured at the top and lashed or buttoned in place.

(8) A structure is considered open to the weather if:

(i) Both sides of the structure are open and not fitted with any means of closing other than temporary covers meeting the requirements of paragraphs (d)(4), (5), and (6) of this section;

(ii) The openings are directly across from each other, are not separated by a bulkhead or bulkheads, and do not have any permanent obstruction within two and one-half feet of either opening; and

(iii) The openings have a continuous height of at least three feet, or the full height of the structure, whichever is less, and either extend the full length of the structure or each have an area of 60 square feet.

(e) Open space between the shelter deck and the uppermost complete deck. (1) Space that is between the shelter deck and the uppermost complete deck and that is under cover (sheltered) but open to the weather is exempt from tonnage when all openings in the uppermost complete deck are provided with a watertight means of closing.

(2) A space is considered “open to the weather” under paragraph (e)(1) of this section when the shelter deck above the space has a middle line opening which conforms to the following:

(i) The middle line opening must be at least four feet long in the clear and at least as wide as the after cargo hatch on the shelter deck, but not less than one-half the width of the vessel at the midpoint of the length of the opening. The opening may have rounded corners not exceeding a nine inch radius. When a greater radius is required by the Coast Guard or a Coast Guard recognized classification society under § 42.05-60 of this chapter, notification of that requirement must be submitted to the Commandant.

(ii) The middle line opening must be located so that the distance between the aft edge of the middle line opening and the vessel's stern is not less than one-twentieth of the tonnage length of the vessel and the distance between the fore edge of the opening and the vessel's stem is not less than one-fifth of the tonnage length of the vessel.

(iii) The middle line opening must not be within a structure of any type.

(iv) If the middle line opening is guarded by rails or stanchions, the rails and stanchions must not be used to secure or assist in securing a cover over the opening.

(v) The coaming of the middle line opening must not exceed one foot mean height above the shelter deck. Bolts must not pass through the stiffeners or flanges on the coaming, nor may there be any other attachments on the coaming for fastening a cover. Portable wood covers may be fitted over the middle line opening if held in place only by lashings fitted to the under side of the covers. Metal covers may be fitted if held in place only by hook bolts spaced not less than 18 inches apart that pass through the cover and hook over angle stiffeners or flanges fitted to the outside of the coaming. Battening, caulking, seals, or gaskets of any material may not be used in association with any middle line opening cover.

(vi) The space below the middle line opening must have a minimum length of four feet throughout its entire breadth and height and be in the clear at all times.

(vii) A scupper having a five inch minimum inside diameter and fitted with a screw down non-return valve geared to and operated from the shelter deck must be fitted on each side of the upper deck in way of the middle line opening.

(3) When the shelter deck space forward or aft of the middle line opening is divided by interior bulkheads, only those compartments with at least two openings that progress to the middle line opening are considered “open to the weather” under paragraph (e)(1) of this section. Each required opening must be at least three feet wide and at least four feet high in the clear, must not have a coaming height of more than two feet, and must not be fitted (except as provided in paragraphs (d)(4), (d)(5), and (d)(6) of this section) with any means of closing. Other compartments within the shelter deck space are not considered “open to the weather” under paragraph (e)(1) of this section.

(f) Water ballast spaces. A space, regardless of location, adapted only for water ballast and not available for stores, supplies, fuel, or cargo (other than water to be used for underwater drilling, mining, and related purposes, including production), upon request, may be exempt from tonnage if the following are met:

(1) The space must be available at all times only for water ballast that is piped through a system independent of other systems (except fire fighting and bilge suction systems). Pumps, pipes, and other equipment for loading and unloading water ballast must be of a size suitable for the efficient handling of the water ballast within a reasonable time frame. All manholes providing access to a water ballast space must be oval or circular and not greater than 34 inches in diameter. Except for those on a deck exposed to the weather, the manholes may have a coaming not exceeding six inches in height. Existing hatches over spaces being converted to water ballast spaces must have a watertight cover plate welded to the hatch and a manhole, as described in this paragraph, fitted in the plating.

(2) The primary purpose of the water ballast must be to afford a means of maintaining the vessel's stability, immersion, trim, pre-loading conditions, or seakeeping capabilities.

(3) If the space is in a vessel that is subject to inspection under 46 U.S.C. 3301,the.

(4) If the total of all water ballast spaces to be exempted from tonnage exceeds 30 percent of the vessel's gross register tonnage (as calculated under this subpart without any allowance for water ballast), a justification of the operating conditions that require the water ballast must be submitted to the measuring organization for approval. Although a single condition may justify all water ballast spaces, several conditions may be necessary in other cases. However, a particular tank is not justified by a condition if another tank already justified by another condition could be used as effectively. The justification must—

(i) Designate the vessel's service;

(ii) Explain for what purpose under paragraph (f)(2) of this section the water ballast is being used;

(iii) Include the capacity, tank arrangement, and piping plans for the vessel;

(iv) Include a statement certifying that the space will be used exclusively for water ballast as prescribed by this section;

(v) If water ballast is used for stability, describe each loading condition and the resultant metacentric height (GM) and include calculations;

(vi) If water ballast is used for immersion or trim, describe those conditions and include loading and trim calculations;

(vii) If water ballast is used for pre-loading, describe how it is used and include strength and weight calculations; and

(viii) If water ballast is used for seakeeping, describe each loading condition, GM, period of roll, and, if speed is involved, speed versus trim and draft and include calculations.

(5) If the water ballast space or its use, purpose, or piping are changed, the vessel owner or operator must report the change promptly to a measurement organization listed in § 69.15 for a determination as to whether a tonnage remeasurement is required. Changes in vessel service must also be reported if a water ballast justification was required to be submitted for the vessel.

(g) Methods for measuring exempt spaces. (1) If the exempt space is located within the superstructure, the exempt space is measured using the same procedures used to measure superstructure tonnage under § 69.113.

(2) If the exempt space is located between-deck, the space is measured using the same procedures used for between-deck tonnage under § 69.111(c), except that the length of the exempt space is divided into the even number of spaces most equal to the number of spaces into which the between-deck was divided.

(3) If the exempt space is located under-deck, the space is measured using the same procedures used for under-deck tonnage under § 69.109, except that the length of the exempt space is divided into the even number of spaces most equal to the number of spaces into which the under-deck was divided, and the zone of influence method must be applied if the ordinary frames upon which the under-deck breadth measurements are based do not have the same depth of frame.

(a) Purpose. This section lists the requirements for spaces (other than propelling machinery spaces under § 69.121) which, though included in calculating gross register tonnage (i.e., are not exempt under § 69.117), are deducted from tonnage in deriving net register tonnage.

(b) General. (1) A deductible space must be used exclusively for, and be reasonable in size for, its intended purpose.

(2) When a space is larger than necessary for the safe and efficient operation of deductible equipment, only the space occupied by the equipment plus a two foot maximum working space on each side of the equipment, if available, is deductible.

(3) Space specified in this section may be located anywhere within the vessel, unless otherwise specified.

(c) Anchor gear. A space below the line of the uppermost complete deck occupied by the anchor gear, capstan, windlass, and chain locker is deductible. A fore peak used exclusively as chain locker is measured by the method prescribed under § 69.117(g)(3).

(d) Boatswain's stores. A space containing oils, blocks, hawsers, rigging, deck gear, or other boatswain's stores for daily use is deductible. The maximum deduction allowed for vessels less than 100 gross register tons is one ton and, for vessels 100 gross register tons or over, is one percent of the gross register tonnage, not to exceed 100 tons.

(e) Chart room. A space for keeping charts and nautical instruments and for plotting the vessel's course is deductible. For a combined wheelhouse and chart room, that part not exempted as wheelhouse under § 69.117(b)(9) is deductible. For small vessels in which the only space for a chart room is in a cabin or saloon, one half the space not to exceed 1.5 tons is deductible as chart room.

(f) Donkey engine and boiler. Donkey engine and boiler space is deductible when connected with the main (non-cargo) pumps of the vessel, except as follows:

(1) If the space is within the engine room or within the casing above the engine room and if the donkey engine is an auxiliary to the main propelling machinery, the space is an engine room deduction under § 69.121(b).

(2) If the space is above the line of the uppermost complete deck and if the donkey engine is not an auxiliary to the main propelling machinery, the space is exempt under § 69.117(b).

(g) Spaces for the exclusive use of officers or crew. (1) The following spaces, regardless of their location (unless otherwise noted), are deductible if not used by passengers:

(i) Sleeping rooms.

(ii) Bathrooms with a bath tub or shower but without a water closet.

(iii) Water closets below the line of the uppermost complete deck serving more than one person, with or without a bath tub or shower. Water closets, regardless of location, that serve only one person or that are accessible only through a stateroom or bedroom serving one person are considered as part of the space they serve and are deductible only if that space is deductible.

(iv) Clothes drying rooms.

(v) Drinking water filtration or distilling plant below the line of the uppermost complete deck.

(vi) Hospitals.

(vii) Mess rooms.

(viii) Office of the chief engineer.

(ix) Oil skin lockers.

(x) Pantries.

(xi) Recreation rooms.

(xii) Smoking rooms.

(xiii) Galleys below the line of the uppermost complete deck.

(2) Shops for engineers, carpenters, plumbers, or butchers and offices for clerks, pursers, or postmasters are not deductible, wherever located.

(h) Master's cabin. The master's sleeping room, dressing room, bathroom, observation room, reception room, sitting room, water closet, and office are deductible.

(i) Radio room. Spaces in which radio apparatus is installed and messages are sent and received and which may provide off-duty operator accommodations are deductible.

(j) Steering gear. Spaces for steering gear below the line of the uppermost complete deck are deductible.

(k) Generators. Spaces for generators below the line of the uppermost complete deck are deductible regardless of what space the generators serve. These spaces may include other equipment necessary for the generator's operation.

(l) Pump room. Spaces below the line of the uppermost complete deck containing pumps that are not capable of handling cargo and that are not fuel oil transfer pumps considered part of the propelling machinery under § 69.121(b)(2)(v) are deductible.

(m) Sail stowage. A space for stowing sails on a vessel propelled only by sails is deductible up to two and one-half percent of the vessel's gross register tonnage.

(n) Waste material space. (1) A tank or collection space, regardless of location, used for the carriage or collection of sewage, garbage, galley waste, trash, slop-oil mixture, tank cleaning residue, bilge residue, or other waste material generated aboard the vessel is deductible.

(2) Space below the line of the uppermost complete deck used exclusively to separate, clarify, purify, or otherwise process waste material generated aboard the vessel is deductible.

(o) Passageways. A passageway or companionway is deductible—

(1) If it serves deductible spaces only; or

(2) If it serves deductible spaces and is also the sole means of access to one of the following non-deductible spaces:

(i) Lockers of less than two tons each, containing medicine, linen, mops, or other items for the free use of the crew.

(ii) A ship's office.

(iii) Spare rooms (not exceeding two) used by a pilot, customs officer, reserve engineer, or employee or agent of the vessel's owner or operator.

(p) Markings for deductible spaces. (1) Each space deducted under this section must be marked with the words “Certified ______” (inserting the space designation, such as “Seaman”, “Generator”, Office of Chief Engineer”, “Hospital”, or “Anchor Gear”). If a deductible space berths more than one crew member, the marking must indicate the number of crew members berthed, such as “Certified ______ Seamen” (inserting the number of crew).

(2) The abbreviations “Cert.” for “certified” and “W.C.” for “water closet” may be used.

(3) The markings must be in Roman letters and Arabic numerals at least 1/2 inch in height, must be painted in a light color on a dark background, must be embossed, center-punched, carved, or permanently cut in a bulkhead or metal plate, and must be placed in a legible location over a doorway on the inside of the space. A metal plate, if used, must be permanently fastened in place by welding, riveting, lock screws, or a Coast Guard-approved bonding agent.

(q) Method for measuring deductible spaces. (1) A rectangular space must be measured by taking the product of its length, breadth, and height.

(2) A space with curved sides on or above the tonnage deck is measured according to § 69.109.

(3) Space less than 15 feet in length may be measured by any practical method.

(4) Spaces below the tonnage deck exceeding 15 feet in length and bounded by a curved surface conforming to the side of the vessel must be measured by the formula used for measuring the superstructure under § 69.113.

(5) The height of a space located on a platform in the hull must be measured from the top of the bottom hull frames, if the platform is used only to form a flat surface at the bottom of the space, if the platform is not more than one foot above the top of the bottom frames, and if the space below the platform is not usable.

(6) The height of a space is measured through any ceiling, paneling, false overhead, or other covering, to the space's structural boundary, unless the space enclosed by the covering is available for a non-deductible use.

(a) General. The engine room deduction is either a percentage of the vessel's total propelling machinery spaces or a percentage of the vessel's gross register tonnage.

(b) Propelling machinery spaces. (1) Propelling machinery spaces are the spaces occupied by the main propelling machinery and auxiliary machinery and spaces reasonably necessary for the operation and maintenance of the machinery. Propelling machinery spaces do not include spaces for fuel tanks, spaces exempt from tonnage under § 69.117, and spaces not used or not available for use in connection with the propelling machinery.

(2) Propelling machinery spaces are—

(i) Space below the crown. The crown is the top of the main space of the engine room to which the heights of the main space are taken. The crown is either the underside of a deck or, if the side bulkheads are sloping, the uppermost point at which the slope terminates. (See § 69.123, figures 13 and 14.)

(ii) Framed-in space located between the crown and the uppermost complete deck and used for propelling machinery or for the admission of light or air to propelling machinery spaces. (See § 69.123, figures 13 and 14.)

(iii) Shaft tunnel space and thrust block recess space.

(iv) Space below the uppermost complete deck used for escape shafts or trunked ladderways leading from the aft end of the shaft tunnel to the deck above.

(v) Space containing a fuel oil transfer pump located in a separate space and not used for bunkering the vessel. When the pump serves both ballast and fuel oil, only one-half of the pump's space is considered a propelling machinery space.

(vi) Spaces containing fuel oil settling tanks used solely for the main boilers. The space must not exceed one percent of the vessel's gross tonnage.

(vii) Spaces for engineers' stores and workshops located below the uppermost complete deck and either open to a propelling machinery space or separated from a propelling machinery space only by a screen bulkhead. The space must not exceed three-quarters of one percent of the vessel's gross register tonnage.

(viii) Framed-in space located above the line of the uppermost complete deck and used for propelling machinery or for the admission of light or air to a propelling machinery space, when requested under paragraph (d) of this section.

(ix) If the propelling machinery is boxed-in below the tonnage deck, the boxed-in space plus the spaces outside of the boxing for the shaft, auxiliary engines, and related propelling machinery. If a portion of the boxed-in space extends above a platform or partial deck that is below the uppermost complete deck, that portion is also considered part of the propelling machinery space.

(c) Methods for measuring propelling machinery spaces. (1) If the propelling machinery space is bulkheaded off or is not larger than necessary for the safe operation and maintenance of the propelling machinery, the entire space, or, if bulkheaded off, the portion bulkheaded off, is measured for the engine room deduction.

(2) If the propelling machinery space is not bulkheaded off or is larger than necessary for the safe operation and maintenance of the propelling machinery, only the space occupied by the propelling machinery itself plus a working space of two feet, if available, on each side of the propelling machinery is measured for the engine room deduction. If the working space overlaps another working space not related to the propelling machinery, only one-half of the overlapping working space is included in the propelling machinery space. The height of the working space is measured as provided in paragraph (c) of this section.

(3) If the propelling machinery is located in more than one space, each space must be measured separately.

(4) If the propelling machinery is located in a space with a step in the bottom or side lines, each stepped portion of the space must be measured separately.

(5) The length of a space under paragraph (c)(1) of this section is measured from the bulkhead just forward of the propelling machinery to the bulkhead just aft of the propelling machinery. The length of a space under paragraph (c)(2) of this section is measured from the forward edge of the working space to the aft edge of the working space.

(6) If the boundaries of the propelling machinery space form a rectangle, the product of the length, breadth, and height, divided by 100, is the tonnage of the space.

(7) If the boundaries of the propelling machinery space are continuous fair lines, heights are measured at the fore and aft ends and at the center of the space from the bottom frames, floors, or tank top of a double bottom up to the line of the crown. A breadth is measured at half-height of each height. The product of the length, mean breadth, and mean height, divided by 100, is the tonnage of the space.

(8) If the propelling machinery space is in the aft end of the hull, extends from side to side of the hull, and has a continuous bottom line, the length of the space is divided into the even number of equal parts most nearly equal to the number of parts that the tonnage length under § 69.109(g) was divided. The tonnage is then calculated by the same method used for calculating the under-deck tonnage in § 69.109(l).

(9) The tonnage of a framed-in space located between the crown and the uppermost complete deck and used for propelling machinery or for the admission of light or air to the propelling machinery space, is the product of its length, breadth, and height, divided by 100.

(10) The tonnage of a shaft tunnel, or a thrust block recess, having a flat top is the product of its length, breadth, and height, divided by 100. If the shaft tunnel or thrust block recess top is not flat, the space above must be calculated by using the appropriate geometrical formula. If the space aft of the shaft tunnel extends from side to side of the vessel, the tonnage of the space is found by the formula for measuring peak tanks in § 69.109(l).

(11) The length and breadth of the space for a shaft tunnel, or a thrust block recess, when not cased is that which is necessary for maintenance of the shaft. The height allowed for thrust block recess space must not exceed seven feet. The mean height allowed for the shaft tunnel space must not exceed six feet. In a multi-screw vessel where the shaft tunnel or thrust block recess space is open from side to side, measure only the space used for purposes of propelling the vessel.

(12) When the propelling machinery is on a bed at the vessel's bottom, the height of the propelling machinery space is measured from the top of the bottom frames or floors.

(d) Request to treat certain framed-in engine room spaces as part of a propelling machinery space. (1) Under § 69.117(b)(4), framed-in spaces located above the line of the uppermost complete deck and used for propelling machinery or for admitting light or air to a propelling machinery space are exempt from inclusion in tonnage. However, upon written request to a measurement organization listed in § 69.15, the vessel owner may elect to have these spaces included in calculating the gross register tonnage, then deducted from the gross register tonnage as propelling machinery spaces under paragraph (b)(2)(viii) of this section when calculating the net register tonnage.

(2) The framed-in space must be safe, seaworthy, and used only for propelling machinery or for the admission of light or air to the propelling machinery space. The length of the space must not exceed the length of the propelling machinery space and the breadth must not exceed one-half of the extreme inside midship breadth of the vessel. Portions of the framed-in space that are plated over are not included in the propelling machinery space.

(3) To exercise the option in paragraph (d)(1) of this section, all of the framed-in space need not be treated as propelling machinery space, but only that portion required to entitle the vessel to have 32 percent of its gross register tonnage deducted as an engine room deduction under paragraph (e) of this section.

(e) Calculating the engine room deduction. (1) The engine room deduction is based on a percentage of the vessel's gross register tonnage or a percentage of the total propelling machinery space.

(2) For vessels propelled in whole or in part by screw—

(i) If the total propelling machinery space is 13 percent or less of the vessel's gross register tonnage, deduct 32/13 times the total propelling machinery space;

(ii) If the total propelling machinery space is more than 13 but less than 20 percent of the vessel's gross register tonnage, deduct 32 percent of the vessel's gross register tonnage; or

(iii) If the total propelling machinery space is 20 percent or more of the vessel's gross register tonnage, deduct either 32 percent of the vessel's gross register tonnage or 1.75 times the total propelling machinery space, whichever the vessel owner elects.

(3) For vessels propelled in whole or in part by paddle-wheel—

(i) If the total propelling machinery space is 20 percent or less of the vessel's gross register tonnage, deduct 37/20 times the total propelling machinery space;

(ii) If the total propelling machinery space is more than 20 but less than 30 percent of the vessel's gross register tonnage, deduct 37 percent of the vessel's gross register tonnage; or

(iii) If the total propelling machinery space is 30 percent or more of the vessel's gross register tonnage, deduct either 37 percent of the vessel's gross register tonnage or 1.5 times the total propelling machinery space, whichever the vessel owner elects.