46 CFR §69.207

1. (a)All lengths and depths must be measured in a vertical plane at centerline and breadths must be measured in a line at right angles to that plane. All dimensions must be expressed in feet and inches to the nearest inch or in feet and tenths of a foot to the nearest tenth of a foot.
2. (b)For a multi-hull vessel, each hull must be measured separately for overall length, breadth, and depth and the vessel as a whole must be measured for registered length, breadth, and depth.
3. (c)The Coast Guard may verify dimensions of vessels measured under this subpart.