46 CFR 137.300: Drydock and internal structural examination intervals

Last reviewed: October 14, 2026

After obtaining a COI, each towing vessel must undergo a drydock and internal structural examination at set intervals. The interval depends on how long the vessel is exposed to salt water. The cognizant OCMI may require additional examinations when he or she discovers or suspects damage or deterioration to hull plating or structural members that may affect seaworthiness or fitness for the route or service.

Applies toEach towing vessel that has obtained a COI, regardless of the option chosen to obtain the COI.

What it says

  1. Regardless of the option chosen to obtain a COI, each towing vessel must undergo a drydock and internal structural examination at the stated intervals once it has obtained a COI.

    46 CFR 137.300(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:”

  2. A vessel exposed to salt water more than 6 months in any 12-month period since the last examination or initial certification must be examined at least twice every 5 years, with not more than 36 months between examinations.

    46 CFR 137.300(a)(1)“must undergo a drydock and internal structural examination at least twice every 5 years, with not more than 36 months between examinations.”

  3. A vessel exposed to salt water not more than 6 months in any 12-month period since the last examination or initial certification must be examined at least once every 5 years.

    46 CFR 137.300(a)(2)“must undergo a drydock and internal structural examination at least once every 5 years.”

  4. The cognizant OCMI may require additional examinations 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.

    46 CFR 137.300(b)“damage or deterioration to hull plating or structural members that may affect the seaworthiness or fitness for the route or service of a vessel.”

  5. These additional examinations may include an internal structural examination of any affected space of a vessel, including its fuel tanks.

    46 CFR 137.300(b)(1)“An internal structural examination of any affected space of a vessel, including its fuel tanks;”

  6. These additional examinations may include an adjustment of the drydock examination intervals to monitor the vessel's structural condition.

    46 CFR 137.300(b)(3)“An adjustment of the drydock examination intervals to monitor the vessel's structural condition.”

Common questions

How often must a towing vessel be drydocked if it operates mostly in salt water?

A vessel exposed to salt water more than 6 months in any 12-month period must be examined at least twice every 5 years. No more than 36 months may pass between examinations.

“must undergo a drydock and internal structural examination at least twice every 5 years, with not more than 36 months between examinations.”

How often is a drydock exam required for a vessel with limited salt water exposure?

A vessel exposed to salt water not more than 6 months in any 12-month period must be examined at least once every 5 years.

“must undergo a drydock and internal structural examination at least once every 5 years.”

Can the OCMI require extra drydock or structural exams?

Yes. The cognizant OCMI may require additional examinations when 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.

“damage or deterioration to hull plating or structural members that may affect the seaworthiness or fitness for the route or service of a vessel.”

The text of 46 CFR 137.300

Electronic Code of Federal Regulations (eCFR), current as of April 16, 2026 · Read it on eCFR

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.

The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of April 16, 2026. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.