What is a UWILD inspection and how often is it required?

Every classed vessel or floating unit — from a supply vessel to an FPSO — must periodically demonstrate to its classification society that the hull and its appendages are in acceptable condition. The traditional way is dry-docking. The problem: taking a unit out of operation costs days or weeks of downtime, mobilization and schedule risk. The UWILD (UnderWater Inspection in Lieu of Drydocking) exists exactly for that — performing the survey afloat, with the unit on station, with the result accepted by class in place of the docking.

How often is a UWILD required?

The class cycle runs in five-year periods, with intermediate surveys between renewals. Classification societies (ABS, DNV, Lloyd's Register, among others) accept in-water surveys in lieu of certain dockings — typically the intermediate one — subject to the unit type, age, class notation and prior approval of the inspection program. For units that cannot leave station, such as FPSOs, the in-water survey is not a convenience but the standard practice throughout their life cycle.

The practical rule: the exact periodicity is defined by your classification society and the unit's notation. A good UWILD provider coordinates the scope directly with class and the operator before mobilizing — never the other way around.

What gets inspected

• Hull plating and weld seams — deformation, corrosion, mechanical damage and coating condition.
• Sea chests and gratings — blockage, corrosion and general condition.
• Thrusters, propellers, rudder and appendages — damage, fouling, visible clearances.
• Cathodic protection system — condition and depletion of sacrificial anodes.
• Biofouling — level and distribution, which also drives fuel consumption.
• Ultrasonic thickness measurements (UT) — where the scope requires it, to estimate remaining steel.

ROV or divers?

Both methods are accepted; the difference lies in risk and record quality. With an inspection ROV there is no personnel in the water: operational risk drops immediately, the working window widens, and the high-definition video record is continuous, referenced by hull zone and repeatable between campaigns — something class and the operator appreciate when comparing condition year over year. Divers remain the option when tactile tasks or local cleaning are required. In practice, many campaigns combine both. At HPS we run the survey with the SRV-8X Optimus mini-ROV, built to work around hulls and appendages in confined spaces.

Deliverables you should demand

• HD video and photography organized by hull zone, with date and position traceability.
• Hull condition and biofouling summary.
• Thickness measurement results, where applicable.
• A technical report with findings, comparison against the previous campaign and recommendations — in a format acceptable to the classification society.

How a well-run UWILD is planned

Three steps separate a clean campaign from a costly repeat: first, agree the scope with class (which zones, which measurements, what witnessing the surveyor requires); second, prepare the unit — visibility, current and simultaneous operations define the working window; third, mobilize a proven spread, with backup and a plan B. Performed afloat, the cost of a failed campaign is low compared to a dry-dock — but the cost of repeating it against an expiring class window is not.

Is your unit's intermediate survey approaching, or does your FPSO require its periodic inspection? Our team runs UWILD across the Gulf of Mexico with our own ROV, mobilization from Ciudad del Carmen and class-ready reporting.