UWILD: In-Water Survey in Lieu of Drydocking

You have a hull survey coming due, but the drydock schedule is tight and the yard quote is painful. For certain vessels, the Coast Guard allows the underwater portion of the required five-year inspection to be done in the water, without pulling the boat. That is the UWILD — Underwater Inspection in Lieu of Drydocking. This page explains what the regulation actually permits, how the survey is run, what class and Coast Guard expect from the dive team, and how the pricing tends to break down. It is written for the person writing the specification or approving the invoice, not for the diver in the water. If you are a port engineer, a municipal water superintendent, a facilities manager, or a vessel owner, this will help you plan the job and avoid surprises.

What UWILD Actually Covers

UWILD is not a substitute for a full drydocking. It is a focused underwater examination of the hull, through the use of divers, ROVs, or a combination, to verify structural integrity and condition of appendages. The vessel stays afloat. The surveyor — usually an ABS, DNV, Lloyd's, or Coast Guard inspector — reviews the video and stills, plus the diver's written report, to make a determination. It does not cover internal structure, shafting, or rudder bearings in way of the stern tube unless those items are specifically opened for inspection. If the underwater survey reveals damage, coatings failures beyond acceptable limits, or significant marine growth, the surveyor can require a drydocking anyway. The regulation at 46 CFR 71.50-3 applies to vessels under U.S. flag; foreign flag vessels follow their class society's equivalent rules. The key is that the in-water exam is a condition-based alternative, not a blanket exemption.

The Five-Year Cycle and 46 CFR 71.50-3

Under the rules, a vessel in ocean or coastwise service typically needs two drydockings in any five-year period. The first one is a regular drydocking. The second can be replaced by a UWILD, provided the vessel meets the criteria in the regulation. That is the five-year cycle: one out-of-water exam, one in-water survey. This is not a loophole; it is a structured alternative that has been in the rules for decades. The exact dates are set by your Certificate of Inspection, based on the anniversary of the original build or last survey. You have to request the UWILD in advance and get the Officer in Charge, Marine Inspection (OCMI) to approve it. Practical things matter: the water depth must be adequate for the draft, the water must be clear enough for video, and the bottom must be free of heavy marine growth. A good operator will tell you early if the site does not support the survey. The five-year cycle explained goes into more detail on scheduling windows.

How the Survey Is Conducted: Divers vs ROV

Most UWILD surveys are done by commercial divers using underwater video and digital stills. The diver works in a team: at least two divers, with one in the water and one tending, plus a supervisor on deck. The operation must comply with OSHA 29 CFR 1910 Subpart T and ADCI consensus standards for dive team competency and supervision. For a class survey, the surveyor either watches the live video feed or reviews the recorded footage immediately after the dive. The diver will swim overlapping lanes along the hull, paying particular attention to the boot top, waterline, through-hull fittings, sea chests, rudder, propeller, shaft, and any signs of buckling or corrosion. ROVs are increasingly used, especially where visibility is poor, currents are strong, or access is tight. An ROV can cover more ground in less time, but it still requires a trained operator and a dedicated safety watch. The important trade-off is that an ROV can only record; a diver can physically probe suspicious areas, clean marine growth, and take close-up measurements. A common approach is to use the ROV to sweep the hull, then send a diver in for targeted inspection where the ROV shows a potential problem. You should ask your survey provider which method they propose, and why. The inspection contractors listed here can handle either approach.

What 'Class Approved' Means for Your Vessel

If your vessel is classed, the ABS, DNV, or Lloyd's surveyor must approve the dive company and the individual divers who will do the work. That is where "class approved" comes in. It is not a generic certification. Each class society has its own acceptance criteria for commercial diving firms. They want to see that the company has experience with hull surveys, that its procedures meet the society's survey requirements, and that the dive team includes at least one person who can interpret what they are seeing. For U.S. flag vessels, the Coast Guard also has to accept the firm. In practice, this means you should verify two things before you sign: the dive company's insurance and safety record, and the qualifications of the supervisor. The term "class approved" does not mean the diver is a class surveyor; it means they are recognized by that class society to carry out the underwater portion of the survey. The post on what class approved really means breaks down the differences between class societies. Do not rely on a scuba certification. That is irrelevant to commercial diving. You need personnel who have passed a recognized commercial dive school and have logged hours on actual vessel hulls.

How Pricing Is Structured

UWILD pricing is not a flat rate. It depends on vessel size, water visibility, current, access, and whether you need an ROV or diver. The dive company will quote a mobilization fee and a daily rate. The daily rate typically covers the dive team, the surface support, the boat or barge, and the basic video equipment. If tides or currents limit the dive window to a few hours a day, you pay for the day even if the dive time is short. A clean hull in protected water with good visibility can be done in one day. A large vessel with heavy marine growth, or a location with a strong current, can take two or three days. You will also pay for any special tools, such as a cleaning brush, a thickness gauge, or an ROV with a manipulator arm. The surveyor's time is usually billed separately, either by the dive company or directly by the class society. Ask about the surveyor's travel and standby costs. The most common surprise is a second day because the first day was spent cleaning the hull enough to see it. That is why the ship husbandry and in-water repair firms often bundle cleaning and survey. You can also cut the required exams in half using an ROV survey under the class society's rules, as explained here. That can reduce the total cost, but only if the class accepts the ROV-only approach for your specific vessel.

When UWILD Is Not an Option

The regulation allows UWILD only for certain vessels. It is not available for every hull. For example, passenger vessels with more than 24 overnight passengers, or vessels carrying certain hazardous cargoes, still require a drydocking. The surveyor also has the authority to reject a UWILD if conditions are not suitable. Water depth is a common reason. The vessel must be able to float at the required draft with enough clearance under the keel for the diver to pass and inspect the bottom. If the berth is in a river with soft mud, the vessel may settle at low tide, which makes the UWILD unsafe. Another dealbreaker is poor visibility. If the diver cannot see more than a few inches, the survey is not meaningful. You also cannot use UWILD if the vessel has known structural issues that have been deferred. The survey is intended for vessels in reasonably good condition, not as a way to avoid fixing something. A good dive firm will tell you upfront if a UWILD is likely to be denied. It is better to know that before you mobilize. Ask the class surveyor for a preliminary opinion on the vessel's eligibility before you schedule the dive. The older the vessel, the more likely a drydock is required.

UWILD questions

How often can a vessel use a UWILD instead of a drydock?

Under 46 CFR 71.50-3, a vessel in ocean or coastwise service is allowed one UWILD in each five-year period, typically as the second of the two required hull examinations. The first exam in the period must be an actual drydocking. The exact schedule depends on your Certificate of Inspection.

Can an ROV perform the entire UWILD without putting a diver in the water?

Yes, if the class society accepts the ROV as the primary survey tool and the water conditions allow a sufficient visual examination. The ROV operator must be trained and the video must be clear enough for the surveyor to assess the hull. Some class societies have specific language regarding ROV-only surveys, and the surveyor has final say.

What qualifications should I look for in a UWILD dive contractor?

The dive company must operate under OSHA 29 CFR 1910 Subpart T and follow ADCI consensus standards for supervision. Divers must have current commercial diving certifications from a recognized school, not a recreational scuba card. For class work, confirm the contractor is accepted by your specific class society, such as ABS, DNV, or Lloyd's.

Is a UWILD always cheaper than a drydocking?

Usually, but not always. A UWILD avoids the yard fee and lost time, but it carries its own costs for dive team, support vessel, and surveyor travel. If the hull requires significant cleaning to make the survey valid, or if the surveyor finds a problem that forces a drydock, the total cost can exceed a planned drydocking. Get a firm quote that includes contingency time.