Section 137.300 - Intervals for drydock and internal structural examinations(a) Regardless of the option chosen to obtain a COI, upon obtaining a COI each towing vessel must then undergo a drydock and internal structural examination at the following intervals:(1) A vessel that is exposed to salt water more than 6 months in any 12-month period since the last examination or initial certification must undergo a drydock and internal structural examination at least twice every 5 years, with not more than 36 months between examinations.(2) A vessel that is exposed to salt water not more than 6 months in any 12-month period since the last examination or initial certification must undergo a drydock and internal structural examination at least once every 5 years.(b) The cognizant OCMI may require additional examinations of the vessel whenever he or she discovers or suspects damage or deterioration to hull plating or structural members that may affect the seaworthiness or fitness for the route or service of a vessel. These examinations may include a drydock examination, including:(1) An internal structural examination of any affected space of a vessel, including its fuel tanks;(2) A removal of the vessel from service to assess the extent of the damage and to affect permanent repairs; or(3) An adjustment of the drydock examination intervals to monitor the vessel's structural condition.