46 CFR §189.40-1

1. (a)Drydock examination means hauling out a vessel or placing a vessel in a drydock or slipway for an examination of all accessible parts of the vessel's underwater body and all through-hull fittings.
2. (b)Internal structural examination means an examination of the vessel while afloat or in drydock and consists of a complete examination of the vessel's main strength members, including the major internal framing, the hull plating, voids, and ballast tanks, but not including cargo or fuel oil tanks.
3. (c)Underwater survey means the examination, while the vessel is afloat, of all accessible parts of the vessel's underwater body and all through-hull fittings.