46 CFR 115.600 - Drydock examination, internal structural examination, and underwater survey intervals.
(b) If your vessel is operated on international voyages subject to SOLAS requirements, it must undergo a drydock examination once every 12 months unless it has been approved to undergo an underwater survey (UWILD) per § 115.615 of this part. If the vessel becomes due for a drydock examination or an internal structural examination during the voyage, it may lawfully complete the voyage prior to the examination if it undergoes the required examination upon completion of the voyage to the United States but not later than 30 days after the examination is due. If the vessel is due for an examination within 15 days of sailing on an international voyage from a United States port, it must undergo the required examination before sailing.
(c) If your vessel is operated on other than international voyages and does not meet the conditions in paragraph (d) of this section, it must undergo a drydock and internal structural examination as follows unless it has been approved to undergo an underwater survey (UWILD) per § 115.615 of this part:
(1) A vessel that is exposed to salt water more than three months in any 12 month period since the last examination must undergo a drydock examination and an internal structural examination at least once every two years; and
(2) A vessel that is exposed to salt water not more than three months in any 12 month period since the last examination must undergo a drydock examination and an internal structural examination at least once every five years.
(d) Whenever damage or deterioration to hull plating or structural members that may affect the seaworthiness of a vessel is discovered or suspected, the cognizant OCMI may conduct an internal structural examination in any affected space, including fuel tanks, and may require the vessel to be drydocked or taken out of service to assess the extent of the damage, and to effect permanent repairs. The OCMI may also decrease the drydock examination intervals to monitor the vessel's structural condition.
(e) For a vessel that is eligible per § 115.625 of this part and the owner opts for an alternate hull examination with the underwater survey portion conducted exclusively by divers, the vessel must undergo two alternate hull exams and two internal structural exams within any five-year period. If a vessel completes a satisfactory alternate hull exam, with the underwater survey portion conducted predominantly by an approved underwater remotely operated vehicle (ROV), the vessel must undergo one alternate hull and one internal structural exam, within any five-year period. The vessel may undergo a drydock exam to satisfy any of the required alternate hull exams.