Bottom Survey and In-Water Survey (IWS)
The bottom survey must make the hull and related items verifiable. In dry dock or afloat, preparation, evidence quality and the applicable regime determine what can be examined and credited.
Operational Explanation
A bottom survey examines the outside of the immersed hull and related items to establish their condition and identify damage or deterioration. Dry dock provides access to surfaces and components that require other means of observation and verification when the ship is afloat.
An In-Water Survey (IWS) is an afloat survey method: it must provide the information required for the survey, rather than just a hull video. The decision covers the applicable regime, location conditions, ship’s arrangements and the method by which the surveyor can identify and assess what is shown.
| Item | What must be verifiable |
|---|---|
| Shell and external structure | Areas examined, corrosion, deformation, contact damage and relevant welds. |
| Rudder and propulsion items | Visible parts, seals and clearance information required for the installed arrangements. |
| Sea chests and related components | Accessible gratings, chests and connections; examinations and evidence required for the survey. |
This is a map of survey objects, not a complete list for every ship. The agreed programme identifies items to examine, supporting information, work and checks to be performed. IACS UR Z3, §§Z3.2–Z3.3.
Regulatory Reference
SOLAS I/10 and HSSC for cargo ships; SOLAS I/7 and HSSC for passenger ships. IACS UR Z3 addresses the class survey of the bottom and related items. Statutory and class requirements must be met within their respective scope; IWS requires acceptance in the specific case.
Under HSSC 2025, §4.6, cargo ships have at least two inspections in five years, no more than 36 months apart; one is associated with renewal. The note to §4.6.2.2 distinguishes the afloat alternative for ESP ships under 15 years, for inspections not associated with renewal. Any extension follows the applicable provisions and does not result from choosing IWS. IMO A.1207(34), §4.6 and notes.
For passenger ships, HSSC 2025, 5.10, normally specifies at least two dry-dock inspections in five years, no more than 36 months apart. An authorised reduction to one for eligible non-ro-ro ships sets a 60-month maximum; the other annual inspections remain due. From age 15, special consideration is needed before crediting an afloat inspection. IMO A.1207(34), 5.10.
An IWS must provide information normally obtained in dry dock. Before confirming it, check visibility, hull cleanliness, area identification and means to examine the required items. Damage or conditions requiring further investigation may necessitate dry-docking: video alone does not guarantee survey credit. IACS UR Z3, in-water surveys.
UR Z3.1.3 requires dry-docking for these examinations of ESP ships aged 15 or over; for other ships of that age it requires special consideration before an afloat alternative. Check category and age before requesting IWS. IACS UR Z3.1.3.
Extended Dry-Docking (EDD) is a separate programme. Recommendation 133 describes the programme’s specific criteria and agreements and is not the general source for every IWS. IACS Recommendation 133, §§1–2.
Scope of Application
This card addresses preparation and understanding of the bottom survey, in dry dock or afloat. Due dates, method and credit depend on ship type, age, ESP regime where relevant, certificates, survey status and applicable Rules.
Do not transfer the cargo-ship schedule to a passenger ship or a class-survey schedule to a certificate without checking its scope. For the individual survey, the Administration/recognised organisation and class confirm their respective conditions.
Procedure / How to Complete It
- Identify the survey due. Gather survey status, certificates, due dates and open conditions; establish the credit requested and the items it covers.
- Agree the method before the work. Submit the IWS proposal, arrangements and available information; check eligibility, the appointed firm and surveyor attendance/control under the applicable regime.
- Prepare ship, location and evidence. Agree water conditions, cleaning, area identification, equipment, images and communication. Make relevant service history and supporting data available for items that cannot be assessed from the image alone.
- Check coverage during examination. Link each finding to an area or component. If visibility, access or communication prevents meaningful assessment, report this and agree the follow-up; do not record an unverified item as examined.
- Manage findings. Identify damage, unexamined items, further examination or repairs required. The surveyor may require dry-docking where the findings warrant it.
- Close documentation and credit. Keep the report, identifiable images, supporting data and survey outcome. Check relevant entries/endorsements and follow residual conditions with assigned responsibility and due date.
Practical Example
An eligible cargo ship has an afloat inspection scheduled. The proposal identifies areas and how information on installed components will be obtained. During examination, a shell area cannot be assessed because visibility is poor: the report records a limitation, not a “satisfactory” result.
The surveyor specifies further evidence or dry-docking according to the findings. The company follows work and documentation through to the formally recorded outcome; having a video does not itself close the survey.
What Typically Goes Wrong
A survey can produce many images but little usable information when location, coverage or evidence quality is missing. Another difficulty arises when work is booked before the regime is clarified or an unexamined area disappears from the final summary.
Confusing IWS and EDD, applying one rule to cargo and passenger ships or applying a UR outside its scope can lead to choosing a method that is not acceptable for the survey due and calculating the due date incorrectly. A commercial inspection can be completed without obtaining the required survey credit.
Common Mistakes Mistake Library
| Mistake | Consequence | How to Avoid It |
|---|---|---|
| Booking a method without confirming eligibility | Completed inspection may not satisfy the survey due. | Establish regime, items, conditions and acceptance before appointment. |
| Video without location or coverage | The examined area cannot be demonstrated. | Link images/evidence to location and examination limitations. |
| Recording an unverified item as satisfactory | The summary conceals missing verification. | Report the limitation and have the surveyor define the follow-up. |
| Treating IWS as an automatic extension or EDD | Due dates and credit are misunderstood. | Separate survey method, EDD programme and due-date provisions. |
What the PSCO Checks
Operational Tips
- Prepare a map of the agreed areas and components so images and findings remain understandable after the survey.
- Check before the work how to obtain information not demonstrated by video, including clearances or seals where required.
- Keep proposal, acceptance, report, defects and closing evidence together; distinguish completed work from credited survey.
Preparation checklist
- Survey, regime, due date and requested credit identified.
- Method and conditions confirmed by the competent parties.
- Areas/components and supporting evidence defined.
- Cleaning, visibility, equipment and communications prepared.
- Report with identifiable coverage, limitations and findings.
- Outcome and residual conditions followed through to closure.
FAQ
Related Topics
Certified substantive revision: 12 October 2026 · page fingerprint 12963ff03089