33 CFR § 183.39 - Persons capacity: Inboard and inboard-outdrive boats.
(a) The persons capacity in pounds marked on a boat that is designed to use one or more inboard engines or inboard-outdrive units for propulsion must not exceed the lesser of:
(2) For boats with a maximum persons capacity less than 550 pounds, the maximum persons capacity determined in the following manner:
(ii) Gradually add weights along one outboard extremity of each passenger carrying area, at the height of the seat nearest the center of that area, but no higher than the height of the gunwale and distributed equally forward and aft of that center in a plane parallel to the floorboards, until the boat assumes the maximum list or trim or both, without water coming aboard.
(iii) Compute the persons capacity in pounds in the following formula: Persons capacity = A/0.6 where A is the total of the weights added in paragraph (a)(2)(ii) of this section.
(b) The maximum persons capacity in whole numbers of persons marked on a boat that is designed or intended to use one or more inboard engines or inboard-outboard units must not exceed the value obtained by adding 32 pounds to the value determined in paragraph (a)(2)(iii), dividing the sum by 141 and rounding off the result to the nearest whole number. If the fraction is less than one-half, round down to the next whole integer and if the fraction is equal to or greater than one-half, round up to the next higher whole integer.