---
kind: "section"
citation: "46 C.F.R. § 28.501"
title: "46"
number: "28.501"
heading: "Substantial alterations."
url: "https://uscodex.org/cfr/46/28.501"
---

# §28.501. Substantial alterations.

- (a) Except as provided in [paragraph (b)](#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)](/cfr/46/28.530.md?p=c..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)](#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.**

## Notes

### Authority

Authority: 46 U.S.C. 3316, 4502, 4505, 4506, 6104, 8103, 10603; DHS Delegation 00170.1, Revision No. 01.4.

### Source

Source: CGD 88-079, 56 FR 40393, Aug. 14, 1991, unless otherwise noted.