UWILD Explained: 46 CFR 71.50-3 and the Five-Year Cycle

By Nadia Fournier, Marine surveyor and insurance adjuster. Reviewed by Amanda McCallister, editor.

Ship Husbandry & In-Water Repair | Underwater Inspection I remember standing on the wing of a 378-footer in Palermo, watching a diver surface through a sheen of diesel from a cracked vent stack. The owner was asking if the UWILD we'd just finished would count as a drydocking. The answer mattered more than the bill. UWILD—underwater inspection in lieu of drydocking—isn't a gimmick. It's a specific regulatory path that lets a passenger vessel swap a drydock for an in-water examination, but only if you follow the rule exactly. Call it a rhythm, not a loophole.

The Rule: 71.50-3 and 71.50-5

The requirement lives in 46 CFR 71.50-3. If you operate a passenger vessel under Subchapter H, that's your drydocking schedule. The alternative—the actual 'UWILD'—is 71.50-5, which lets the Coast Guard approve an underwater survey instead of taking the boat out of the water. These are two separate things. I've seen owners conflate them. First, 71.50-3 sets the interval. It's not a one-and-done. The general pattern is two credited examinations within a five-year period, with a stated maximum interval between them. The practical rhythm is that you keep the hull examined often enough that you never fall out of the five-year window. Don't let anyone tell you it's 'one UWILD per five years'—that's not how the reg reads. Second, 71.50-5 is the approval process. Your request goes to the Officer in Charge, Marine Inspection (OCMI), often through your classification society. ABS, Lloyd's, DNV—they'll want to see the dive plan, the equipment list, and the surveyor's qualifications before they sign off. And this only applies to passenger vessels. Towing vessels under Subchapter M have a different set of inspections, and they don't fall under these paragraphs.

The Five-Year Cycle: How It Actually Works

Start with the drydock interval. The Coast Guard wants to know your underwater hull is sound at a point in time. A UWILD is a snapshot, but because it's a moving vessel, you have to repeat it. The standard pattern is two exams in five years. That might sound like a cycle, but it's really a sliding window. You need to keep at least one credited exam within the last five years, and the interval between any two credited exams can't exceed the maximum the OCMI approved. Here's where it gets real. The maximum interval isn't a fixed number in the reg—it's determined by the conditions of your certificate of inspection and the OCMI's discretion. Some operators assume it's always 30 months or 36 months. I tell clients: read your COI. The key is that you need the UWILD to be 'credited'—and that requires the approval to be in place before you conduct the survey, not after. One digression: I once watched a chief engineer try to use an underwater hull cleaning as a UWILD because the dive team had a camera on the ROV. He couldn't understand why that wasn't 'inspection.' The difference is intent. A cleaning is not an examination, and a videotape of a clean hull doesn't tell you about plate thickness or weld condition. You need the right instruments and the willingness to measure.

What the Survey Actually Involves

The divers are commercial, not recreational. PADI and NAUI cards don't cut it. You need folks who work under 29 CFR 1910 Subpart T, and ideally a team leader who's done structural surveys. They'll run video along the hull, take ultrasonic thickness readings at grid points, and look carefully at the waterline, the shaft seals, the rudder, and the thruster tunnels. The tide matters—if the current's too strong, you're not getting a clean reading. Visibility is the variable. In a muddy river, you're working by feel. A good dive team will have a set of clear polycarbonate boards to deaden the silt. They'll also use a current meter to make sure the diver isn't fighting too much flow. And the diver knows about delta P—that static head thing. The rule is positive isolation and verification, not 'stay clear.' On a passenger vessel, that means the thruster is locked out, and the sea chest is blanked. Then there's the paperwork. The surveyor writes a report that describes the depth of fouling, the condition of coatings, any anodes that are gone, and any cracks. That report goes to the OCMI with the diver's log. If the OCMI doesn't like the visibility or the coverage, you're doing it again. That's where owners lose money.

Costs, Timing, and the Bottom Line

A UWILD day rate can be $2,500 to $5,000 for a commercial dive team, depending on location and vessel size. But the real cost is downtime. You're usually doing this alongside a technical stop, so the question is whether you schedule it to align with the five-year window. I've seen operators pay for a UWILD in January, then end up in drydock in March because the OCMI didn't credit it. That's a waste. The five-year cycle sounds like a lot of time, but it's not. Time slips away. I recommend putting the UWILD on the same scheduled maintenance plan as your main engine overhaul. Write it into the PMS. That way, when the surveyor asks for the record, you can show an unbroken narrative. Remember, UWILD is an exception to the drydocking rule. The Coast Guard gives it, and they can take it away. Treat it like a privilege, not a right.

Frequently Asked Questions

What is UWILD? UWILD stands for Underwater Inspection In Lieu of Drydocking. It's a Coast Guard-approved alternative to hauling a passenger vessel out of the water, governed by 46 CFR 71.50-3 and 71.50-5. How often does a UWILD need to be done? The general pattern is two credited underwater examinations within a five-year period, with the maximum interval between examinations set by the OCMI in your certificate of inspection. Can any dive company perform a UWILD? No. The dive team must be commercial, operating under 29 CFR 1910 Subpart T, and the team leader needs experience with structural hull surveys, not just underwater work. Does a UWILD replace drydocking entirely? No. It's an approved alternative for a specific inspection cycle. The vessel is still subject to the drydocking schedule under 46 CFR 71.50-3, and the UWILD only counts if the OCMI approves it beforehand.