In-Water Survey (IWS) Singapore — Class Hull Condition Survey While Afloat

What Is an In-Water Survey (IWS)?

An in-water survey is a hull condition survey carried out while the vessel remains afloat. Rather than lifting the ship out of the water to examine the underwater body, an IWS brings the inspection to the hull — using remotely operated vehicles (ROVs) and commercial divers to record the condition of the shell plating, coating, appendages and cathodic-protection system from the waterline down to the keel. The output is a systematic photo and video record, referenced to the vessel's plans, that documents the state of the underwater hull at a fixed point in the survey cycle.

The purpose of an IWS is to satisfy periodic hull-inspection requirements without taking the ship out of service. Classification societies build their hull surveys around a rolling programme, and an in-water survey feeds regular, credible condition data into that programme. It confirms that coatings, anodes and structure are performing as expected between the major examinations, and it gives owners and managers an objective basis for planning cleaning, repairs or the next docking.

It is worth being precise about terminology, because "in-water survey" and "UWILD" are often used loosely. An IWS is the broad category — any hull condition survey done in the water. A UWILD (Underwater Inspection In Lieu of Drydocking) is the specific case where an in-water survey is credited in place of a scheduled docking survey, carried out under a class IWS notation and witnessed by an attending surveyor. Put simply: the IWS is the ongoing in-water hull condition survey that supports the continuous-survey cycle, while a UWILD is the one that formally substitutes for a drydock examination.

Why Owners Commission In-Water Surveys

The commercial logic of an in-water survey is straightforward: it keeps the ship trading. Drydocking is expensive and disruptive — it means positioning the vessel, deballasting, taking her off-hire and paying yard fees, often for defects that turn out to be minor. An IWS lets an owner gather the same hull-condition intelligence with the ship alongside a berth or lying at anchor, so a survey that once required a dock booking can now be completed in a normal port call.

Beyond avoiding downtime, an IWS delivers regular, quantified hull data that owners use to run the ship efficiently. A survey records fouling percentage and distribution, the extent of coating breakdown, anode consumption, and any mechanical damage or deformation. That data drives real decisions — when to schedule hull cleaning to recover lost speed and burn less fuel, whether the anodes will last to the next docking, and how the coating is ageing against its specified life. Managed well, this is condition-based maintenance rather than calendar-based guesswork.

Singapore is a natural place to carry out this work. As one of the world's busiest bunkering and ship-repair hubs, the Port of Singapore sees an enormous volume of vessels calling to take fuel, stores and crew, and to sit at designated anchorages. Many of those calls are an opportunity to complete an in-water survey with no deviation from the voyage plan — the ship is already here, and the survey slots into time that would otherwise be idle.

What an In-Water Survey Assesses

An IWS is a structured examination, not a casual look. Each item below is inspected against the vessel's condition history, recorded on video and captured as still imagery, then compiled into a report your technical team and — where relevant — the attending class surveyor can rely on.

How the Survey Is Carried Out

We run in-water surveys with a combination of ROV and diver inspection, matched to the vessel, the berth and the purpose of the survey. An ROV gives efficient, stable coverage of the large flat areas of the hull and safe access to confined or hazardous zones such as sea chests, while divers provide close tactile inspection, anode checks and detailed work around the running gear. Both carry HD video and lighting, and all footage is logged with position references so it can be reviewed later and audited.

Coverage follows a written survey plan built around the vessel's shell expansion and docking plan. The hull is worked systematically — flats, bilge, boot-top, bottom, and each appendage in turn — so that nothing is skipped and the record is complete and repeatable from one survey to the next. This planned approach is what separates a class-grade IWS from a quick underwater look, and it is essential when the survey has to stand up to scrutiny.

Where the survey is for class credit — most importantly a UWILD — an attending class surveyor witnesses the work, in practice by watching the live ROV and diver video feed with two-way communication to direct the team to any item of interest. The vessel must carry the appropriate class IWS notation for the survey to be creditable. For an owner's own condition-monitoring survey, the same rigorous method is applied but no surveyor need attend, and the report is used internally for maintenance and voyage planning.

Where an IWS Fits With Other Underwater Work

An in-water survey rarely stands entirely alone — it sits within a family of underwater hull services that are often scoped together on the same attendance.

Standards and Class Framework

In-water surveys are governed by the requirements of the vessel's classification society. The major societies — ABS, DNV, Lloyd's Register, Bureau Veritas and ClassNK — each publish rules for in-water surveys and issue a class IWS notation that identifies vessels arranged and equipped for underwater examination in lieu of docking. These rules define what may be surveyed afloat, how it is to be recorded, and the conditions under which a surveyor will credit the work.

Above the individual societies, the International Association of Classification Societies (IACS) provides the unified requirements that harmonise how member societies treat hull surveys, including the survey cycle and the treatment of underwater inspection. The diving and ROV operations themselves are conducted to recognised commercial-diving and remote-inspection good practice, including the IMCA D-series guidance that the offshore and marine industry uses for safe, competent underwater intervention. Working within this framework is what makes the survey record acceptable for class purposes and dependable for the owner.

What an In-Water Survey Covers

At a glance, a periodic IWS brings four condition domains together into one afloat attendance.

Why Choose SG Drone Inspections

We are a specialist inspection provider working across facade, industrial and marine environments, bringing disciplined survey method and clean, traceable data to underwater hull work in Singapore.

Frequently Asked Questions