UWILD Explained: Procedure, Requirements & Class Rules

UWILD stands for Underwater Inspection in Lieu of Dry-docking. Classification societies also call it an In-Water Survey (IWS) or bottom survey afloat. It allows a classed ship to satisfy one of the two bottom inspections required in every five-year class period without going into dock — the hull, sea chests, rudder, propeller and stern gear are examined by divers with a live video link while the class surveyor watches from the quay or deck. Done properly, a UWILD replaces a docking that would otherwise cost the owner a week or more of off-hire.

This guide covers the rule basis, which vessels qualify, what the surveyor will require before agreeing to an in-water survey, the step-by-step procedure on the day, what the report contains, and what an operator should budget in time and money. It is written from the diving contractor's side of the job — we carry out UWILDs for Bureau Veritas, ABS, DNV and Lloyd's Register at ports across Africa — so it concentrates on what actually gets a survey credited rather than on the rule text.

The rule basis: two bottom surveys every five years

SOLAS and the classification society rules require the outside of a ship's bottom to be examined twice in each five-year period of the Cargo Ship Safety Construction Certificate, with no more than 36 months between examinations. One of those two examinations — normally the one falling at the intermediate survey — may be carried out afloat as an in-water survey, provided the vessel and the survey meet the society's conditions. The other, at the special (renewal) survey, must be in dry-dock for most ship types. In practice this means a well-run vessel docks once every five years and does a UWILD around the halfway point.

The rules are written by the individual societies and differ in detail. Bureau Veritas describes the requirements under its IN-WATER SURVEY notation, DNV under the class notation IWS, ABS under UWILD, and Lloyd's Register under its In-Water Survey arrangements. The principles are the same across all four; the notation is the important part, because without it the surveyor has no basis to credit an in-water examination.

Which vessels qualify

A vessel can have its intermediate bottom survey done in the water when the following are true. Where any of them is not met, the surveyor will normally require a dry-docking instead.

• •The ship carries the society's in-water survey notation (IWS, IN-WATER SURVEY, UWILD or equivalent), assigned at build or after a dry-dock inspection confirms the hull is arranged for it.
• •The ship is generally under 15 years of age. Older tankers and bulk carriers subject to the Enhanced Survey Programme (ESP) are usually required to dock for both surveys; other ship types over 15 years may be allowed a UWILD case by case, with flag agreement.
• •There is no outstanding condition of class, damage or recommendation concerning the underwater hull, rudder, propeller or stern gear.
• •The previous dry-docking found the hull in a condition that does not need close-up examination in dock — no significant indents, doublers under observation or coating breakdown that must be seen dry.
• •The hull carries the permanent high-visibility markings and the fittings (rudder clearance gauges, stern-tube wear-down access, sea-chest blanking arrangements) that make an underwater examination meaningful.

If you are unsure whether your vessel qualifies, the quickest check is the class certificate: the notation will be listed with the other hull notations. If it is not there, an in-water survey can still be arranged in some cases, but it must be agreed with the society in advance rather than requested from the diving contractor on the day.

What the class surveyor requires

The surveyor's job is to see the same things they would see in a dock, through the diver's camera. Everything on the checklist below exists so that the video evidence is usable and the measurements are equivalent to a docking.

Vessel side

• •Hull markings: permanent, high-visibility marks on the shell identifying frame numbers, tank boundaries, the bilge keel ends and the areas of the flat bottom, so the diver can report exactly where a finding is.
• •Rudder pintle and bearing clearance: a permanent means of measuring the clearances afloat, or arrangements agreed with the society, since these must be reported at every bottom survey.
• •Stern tube bearing wear-down: an accessible means of measuring propeller-shaft wear-down in the water, or a recent reading from the last docking plus a design allowance the surveyor can accept.
• •Sea chests and gratings: gratings that can be removed by divers, and blanking arrangements so sea valves can be examined from inside if required.
• •Trim and draft: the vessel in the lightest safe ballast condition so that as much of the hull as possible is within diver reach and visibility, and the propeller and rudder are accessible.
• •A clean hull: the surveyor must be able to see the plating. Marine growth that hides the surface must be removed, either as a full hull clean beforehand or as spot cleaning of the areas the surveyor asks to see.

Diving contractor side

• •Approval by the society as a service supplier for in-water surveys, with the approval certificate available to the surveyor before the dive.
• •A live, two-way video and voice link between the diver and the surveyor, with continuous recording of the whole survey, not just highlights.
• •Lighting and camera equipment adequate for the visibility at that port — turbid estuary ports need more light and closer passes than clear deep-water ports.
• •Calibrated ultrasonic thickness gauging equipment where the surveyor wants readings, and the means to take rudder and stern-tube measurements.
• •A dive plan agreed with the vessel: sea suctions isolated, propeller and thrusters locked out, the port and the terminal informed and permitted.

Conditions on the day

The surveyor must be satisfied that the visibility and sea state allow a proper examination. If the water is too turbid to see the plating on the camera even with lights, or the current is too strong for the diver to hold position, the survey is postponed rather than credited on poor evidence. This is the most common reason a UWILD slips a day at river and estuary ports, and it is why the choice of port and the tide window matter as much as the diving itself.

The UWILD procedure step by step

• •1. Planning (one to three weeks ahead): the owner requests the in-water survey from the society and confirms the notation; the diving contractor supplies its approval certificate and a dive plan; the port permit for in-water work is applied for; a berth or anchorage with adequate depth and visibility is chosen and the tide window fixed.
• •2. Pre-survey meeting on board: surveyor, master, chief engineer and dive supervisor agree the scope, the lock-outs (propeller, thrusters, sea suctions, cathodic protection if impressed-current), the communication protocol and the abort criteria.
• •3. Hull cleaning as needed: either a full in-water hull clean before the survey or spot cleaning of the areas the surveyor wants to examine closely — welds, bilge keel ends, sea chests, rudder and stern frame.
• •4. General external examination: the diver swims the hull in agreed passes — flat bottom, sides, bow and stern — with the camera showing plating, welds and coating condition, reporting position against the hull markings. The surveyor directs the diver to stop and look closer wherever needed.
• •5. Close-up items: sea chests with gratings removed, rudder and rudder horn, pintle clearances, propeller blades and hub, rope guard, stern seal area, thrusters and tunnels, bilge keels, anodes or ICCP anodes, echo sounder and log fittings, and any area with a previous repair.
• •6. Measurements: rudder pintle and bearing clearances, stern-tube wear-down, and ultrasonic thickness readings on any plating the surveyor selects.
• •7. Findings: any indent, crack, coating failure or wastage is recorded with position, dimensions and video. The surveyor decides on the spot whether it can be accepted, repaired afloat, or requires docking.
• •8. Reporting: the diving contractor issues the survey report with the recorded video, still photographs, measurements and a hull sketch marking findings. The surveyor issues the society's survey statement and the survey is credited on the class records.

How long a UWILD takes

For a typical Handysize to Panamax vessel with a clean hull and good visibility, the underwater examination itself takes six to ten hours and is completed in one working day, usually while cargo operations continue. Add a day if a full hull clean is needed first, and allow for a tide window at river ports where the current only allows diving at slack water. Large tankers, LNG carriers and vessels with extensive flat bottoms can take two days. The report is normally issued within 24 hours of the last dive.

What it costs, and what it saves

The diving contractor's charge for a UWILD at an African port is typically in the range of USD 7,000 to 20,000 depending on the vessel size, the port, whether a hull clean is included and whether the team must travel. The class surveyor's attendance fee is separate. Against this, a dry-docking that the UWILD replaces costs the docking fee, the yard work, the deviation, and — usually the largest item — five to fourteen days of off-hire. Our cost comparison for African ports puts the saving at well above USD 100,000 for most vessel types, and higher for tankers and gas carriers on charter.

Doing a UWILD at an African port

Three practical points from our own work. First, visibility decides the port. Deep-water ports with open-sea water — Kribi, Lekki, Tema, Walvis Bay, Cape Town — give the surveyor clear footage and a fast survey. River and estuary ports — Douala, Lagos Apapa, Port Harcourt, Abidjan's lagoon berths — need lights, slack-water timing and closer passes, and take longer. If the vessel's schedule gives a choice, choose the clear-water port.

Second, permits take time. Most port authorities require a written permit for in-water work, some terminals add their own permit-to-work, and the class surveyor needs notice to attend. A UWILD requested two days before arrival is usually a UWILD at the next port. Two weeks' notice is comfortable.

Third, ask for the surveyor's attendance mode early. Bureau Veritas, ABS, DNV and Lloyd's Register all have surveyors in the main West and Central African ports, but at smaller ports the society may agree to remote attendance over the live video link. That has to be agreed with the society beforehand, not assumed on the day.

Frequently asked questions

What does UWILD stand for?

Underwater Inspection in Lieu of Dry-docking — an examination of a ship's underwater hull carried out afloat by divers with a live video link, accepted by the classification society in place of one of the two dry-dockings required every five years. Societies also call it an in-water survey (IWS) or bottom survey afloat.

How often can a ship do an in-water survey instead of dry-docking?

Once per five-year class period, normally at the intermediate survey. The other bottom survey in the period, at the special survey, must be in dry-dock for most ship types. The interval between any two bottom surveys may not exceed 36 months.

Which classification societies accept UWILD?

All major IACS societies accept in-water surveys for vessels that carry the relevant notation and meet their conditions, including Bureau Veritas, ABS, DNV and Lloyd's Register, for which Cameroon Diving Services holds service-supplier approval. The diving contractor must be approved by the society, and the surveyor attends the survey in person or, where the society agrees, remotely over the live video link.

Can a ship over 15 years old have a UWILD?

Sometimes. Oil tankers and bulk carriers under the Enhanced Survey Programme are generally required to dock for both bottom surveys once they pass 15 years. Other ship types may be allowed an in-water survey after 15 years if the society and the flag agree, usually based on the condition found at the last docking.

What are the main UWILD requirements on the vessel?

The in-water survey class notation; permanent high-visibility hull markings; a means of measuring rudder pintle clearances and stern-tube wear-down afloat; removable sea-chest gratings; a hull clean enough for the plating to be seen; and no outstanding conditions of class on the underwater hull.

How long does a UWILD take and does the ship go off-hire?

Usually one working day of diving for a clean hull in good visibility, with the report within 24 hours. The survey is normally done alongside during cargo operations or at anchor, so the vessel does not go off-hire.

What happens if the divers find damage?

The surveyor assesses the finding on the video. Minor items can be accepted or repaired afloat — underwater welding, doublers, anode replacement. Anything the surveyor cannot accept from the underwater evidence, such as significant indents or cracks in primary structure, results in a condition of class and a requirement to dock.