(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.

[CGD 87-015b, 54 FR 37657, Sept. 12, 1989, as amended by USCG-2014-0688, 79 FR 58281, Sept. 29, 2014; USCG-2011-0522, 81 FR 18726, Mar. 31, 2016]