Regardless of the option chosen to obtain a COI, upon obtaining the initial COI each towing vessel must conduct drydock and Internal structural examinations (ISE) at the appropriate interval based on Fresh or Saltwater Service:
- For freshwater service (exposed to saltwater less than 6 months in any 12-month period since last examination) at least once every 5 years.
- For saltwater service (exposed to saltwater more than 6 months in any 12-month period since last examination) at least twice every 5 years, with not more than 36 months between examinations.
As an alternative, a towing vessel can comply with drydock and ISE requirements by:
- Maintaining a valid load line certificate – see 46 CFR 137.320; or,
- Maintaining class by ABS or another recognized classification society accepted by the Coast Guard – see 46 CFR 137.322.
Note: In instances where a vessel is required to conduct two drydocks and ISEs for salt water service, the allowance to accept load line or class drydock and ISEs only counts for one of the required two examinations.
U.S. vessel owners and operators desiring to utilize an underwater survey in lieu of drydocking (UWILD) should review the guidance in NVIC 1-89, Underwater Survey Guidance. UWILD is an optional compliance option and, if utilized, permits the owner to alternate drydocks with underwater surveys. For instance, a vessel in salt water service that would normally be drydocked at years 2.5, 5, 7.5, 10, 12.5, and 15 could conduct these alternate underwater surveys instead of drydocking at years 2.5, 7.5, and 12.5.
Items to check:
- Valid Load Line Certificate.
- Vessel maintains class and meets RCS rules on drydocking and ISE requirements.
- Complete drydock (or Coast Guard approved UWILD) and ISE at the correct interval:
- Salt-Water: Twice every five (5) years, with not more than thirty six (36) months between examinations.
- Fresh-Water: At least once every five (5) years.
46 CFR 137.300 Intervals for drydock and internal structural examinations
46 CFR 137.320 Vessels holding a valid load line certificate
46 CFR 137.322 Classed Vessels
46 CFR 137.335 Underwater survey in lieu of drydocking
NVIC 1-89, Underwater Survey Guidance