Section 28.501 - Substantial alterations(a) Except as provided in paragraph (b) of this section, a vessel that is substantially altered, including the cumulative effects of all alterations, need not comply with the remainder of this subpart, provided that it has stability instructions developed by a qualified individual which comply with § 28.530 (c) through (e) .(b) A vessel that is substantially altered in a manner which adversely affects its stability, including the cumulative effects of all alterations, need not comply with the remainder of this subpart, provided the stability instructions required by paragraph (a) of this section are based on loading conditions or operating restrictions, or both, which compensate for the adverse affects of the alterations.(c) The following changes to a vessel's lightweight characteristics are considered to adversely affect vessel stability:(1) An increase in the vertical center of gravity at lightweight by more than 2 inches (51 millimeters) compared to the original lightweight value.(2) An increase or decrease of lightweight displacement by more than 3 percent of the original lightweight displacement.(3) A shift of the longitudinal center of gravity of more than 1 percent of the vessel's length.(d) In determining whether or not a vessel's stability has been adversely affected, a qualified individual must, at a minimum, consider the net effects on stability of any: (1) Reduction of the downflooding angle;(2) Increase in the maximum heeling moment caused by fishing gear or weight lifted over the side due to changes in lifting arrangement or capacity;(3) Reduction in freeing port area;(4) Increase in free surface effects, including increased free surface effects due to water on deck associated with any increase in length or height of bulwarks;(5) Increase in projected wind area;(6) Decrease in the angle of maximum righting arm;(7) Decrease in the area under the righting arm curve; and(8) Increase in the surface area on which ice can reasonably be expected to accumulate.