46 CFR §137.335

1. (a)This section applies to all towing vessels subject to this subchapter. If a TSMS is applicable to the vessel, the TSMS may include policies and procedures for employing and documenting an underwater survey in lieu of drydocking (UWILD). A vessel is eligible for UWILD if the Coast Guard determines that:
   1. (1)There is no obvious damage or defect in the hull adversely affecting the seaworthiness or fitness for the vessel's route or service;
   2. (2)The vessel has been operated satisfactorily since the last drydocking;
   3. (3)The vessel is less than 15 years of age;
   4. (4)The vessel has a steel or aluminum hull; and
   5. (5)The vessel is fitted with a hull protection system.
2. (b)The owner or managing operator must submit an application to the cognizant OCMI at least 90 days before the vessel's next required drydock examination. The application must include:
   1. (1)The procedure for carrying out the underwater survey;
   2. (2)The time and place of the underwater survey;
   3. (3)The method used to accurately determine the diver's or the remotely operated vehicle's location relative to the hull;
   4. (4)The means for examining all through-hull fittings and appurtenances;
   5. (5)The condition of the vessel, including the anticipated draft of the vessel at the time of the survey;
   6. (6)A description of the hull protection system; and
   7. (7)The names and qualifications of all personnel involved in conducting the UWILD.
3. (c)If a vessel is 15 years of age or older, the Commandant may approve a UWILD at alternating intervals provided that:
   1. (1)All provisions of paragraphs (a) and (b) of this section are complied with, except that the vessel does not need to be less than 15 years of age; and
   2. (2)During the vessel's drydock examination preceding the underwater survey, a complete set of hull gauging was taken which indicated that the vessel was free from hull deterioration.