46 CFR 169.229 - Drydock examination, internal structural examination, and underwater survey intervals.
(a) Except as provided for in paragraphs (b) through (e) of this section, each vessel must undergo drydock and internal structural examinations as follows:
(1) If your vessel operates in saltwater, it must undergo two drydock examinations and two internal structural examinations within any 5-year period unless it has been approved to undergo an underwater survey (UWILD) under § 169.230 of this part. No more than 3 years may elapse between any two examinations.
(2) If your vessel operated in fresh water at least 50 percent of the time since your last drydocking, it must undergo a dry dock and internal structural examination at intervals not to exceed 5 years unless it has been approved to undergo an underwater survey (UWILD) under § 169.230 of this part.
(b) Vessels with wooden hulls must undergo two drydock and two internal structural examinations within any five year period regardless of the type of water in which they operate. No more than three years may elapse between any two examinations.
(c) If, during an internal structural examination damage or deterioration to the hull plating or structural members is discovered, the Officer in Charge, Marine Inspection, may require the vessel to be drydocked or otherwise taken out of service to further assess the extent of the damage and to effect permanent repairs.
(d) Each vessel which has not met with the applicable examination schedules in paragraphs (a) through (c) of this section because it is on a voyage, must undergo the required examinations upon completion of the voyage.
(e) The Commandant (CG-CVC) may authorize extensions to the examination intervals specified in paragraphs (a) and (b) of this section.