Operational Guide · Registers & Logbooks

# Bottom Survey and In-Water Survey (IWS)

SOLAS requires two bottom inspections every 5 years, with a maximum of 36 months between them: the In-Water Survey can replace a dry dock entry, but only under certain conditions.

bottom survey In-Water Survey SOLAS Chapter I ship's bottom

## Operational Explanation

SOLAS Chapter I, Regulation 10 requires at least two inspections of the ship's bottom in every 5-year period, with a maximum interval of 36 months between two consecutive inspections. Traditionally this inspection takes place in dry dock, but the In-Water Survey (IWS), conducted by divers or ROV with a surveyor following the operations, is accepted as an alternative in many cases, especially as the second check in the five-year cycle (Extended Dry Docking, EDD).

However, the IWS is not an automatic and unconditional substitute for dry docking: if it reveals damage, deterioration, or conditions requiring immediate attention or that can only be reliably assessed out of the water, the surveyor may still require dry dock entry.

Extension to 7.5 years: the Extended Dry Docking regime has been further formalized with IACS Recommendation No. 133, which allows, for ships meeting the requirements, two consecutive In-Water Surveys to be conducted in place of the intermediate dry-docking, extending the maximum interval between two dry dock entries from 5 to 7.5 years, subject to approval from both the Classification Society (IACS members only) and the flag Administration.

## Regulatory Reference

SOLAS Chapter I, Regulation 10: minimum 2 bottom inspections in 5 years, maximum 36 months between two inspections; IACS UR Z10 (series) governs the technical criteria for accepting the In-Water Survey as an alternative, including the conditions for Extended Dry Docking (EDD) up to a maximum of 60 months between two dry-dockings, with an IWS in between. IACS Recommendation No. 133: allows, through two consecutive IWS, the extension of the maximum interval up to 7.5 years, with dual approval from the Classification Society (IACS) and the flag Administration.

## Scope of Application

Every ship subject to SOLAS Chapter I; the admissibility of the IWS as an alternative to dry docking depends on ship type, shaft lubrication systems (the EDD exemption for oil/grease-lubricated shafts requires specific consideration), and approval from the Classification Society/flag Administration.

## Procedure / How to Complete It

1. Verify whether the ship is eligible for the Extended Dry Docking (EDD) regime according to the criteria of its Classification Society.
2. If eligible, request formal approval for the IWS well ahead of the 36-month deadline from the last dry-docking.
3. Organize the IWS with a qualified underwater company and the presence of the Class surveyor, according to the approved protocol.
4. Photograph/film every area inspected, particularly zones subject to greater wear (underwater hull, appendages, sea chests).
5. If the IWS reveals conditions requiring immediate attention, promptly schedule dry dock entry, without waiting for the original deadline.
6. For the extension to 7.5 years under IACS Recommendation No. 133, verify the specific requirements for two consecutive IWS and obtain dual approval from the Classification Society and the flag Administration.

### Diagram: dry-docking vs. In-Water Survey interval (max 36 months between two inspections)

## Practical Example

Example: a ship admitted to the EDD regime, with dry-docking at year 0 and an In-Water Survey planned at year 2.5 (30 months), conducted with ROV and a surveyor live, with no significant findings, allowing the next dry-docking to be postponed up to a maximum of 60 months from the previous one.

## Real Cases

In several cases, an In-Water Survey has revealed hull or appendage damage not visible or adequately assessable without direct out-of-water access, leading the surveyor to require an earlier dry dock entry than originally scheduled: an outcome that confirms the conditional, not automatic, nature of accepting the IWS as an alternative.

## Common Mistakes Mistake Library

Mistake | Consequence | How to avoid it
--- | --- | ---
EDD/IWS approval request submitted too late relative to the 36-month deadline | Inability to organize the IWS in time, forcing an unplanned dry-docking | Submit the approval request well ahead of the deadline
IWS conducted without adequate photographic documentation of critical areas | Difficulty demonstrating hull condition in the event of a later dispute | Systematically document every area inspected during the IWS
Ignoring a surveyor's indication of the need for earlier dry-docking after an IWS with findings | Risk of deterioration not addressed promptly | Immediately schedule dry-docking if required by the surveyor, regardless of the original programme

## PSC Observations

PSCOs may verify the documentation of the last bottom survey (in dock or IWS) and its consistency with the intervals required by SOLAS Chapter I, especially in case of doubts about hull condition.

## Operational Tips

- Submit the EDD/IWS approval request well ahead of the 36-month deadline.
- Photograph every area inspected during the IWS, not only zones that appear problematic.
- Never postpone a dry-docking required by the surveyor following findings during the IWS.

## Checklist

- Eligibility for the EDD regime verified against the Classification Society's criteria
- IWS approval requested with sufficient lead time
- IWS conducted with a qualified underwater company and surveyor present
- Systematic photographic/video documentation of inspected areas
- Earlier dry-docking scheduled if required by the surveyor

## FAQ

What is the maximum interval between two bottom inspections under SOLAS?
36 months, with at least two inspections in every 5-year period, under SOLAS Chapter I Regulation 10.
Does the In-Water Survey always replace dry-docking?
No: it is accepted as an alternative under certain conditions (typically as the second check in the five-year cycle, under the Extended Dry Docking regime), but the surveyor may still require dry-docking if the IWS reveals conditions requiring immediate attention or out-of-water assessment.
Can every ship access the Extended Dry Docking regime?
No: eligibility depends on specific technical criteria of the Classification Society, including considerations on shaft lubrication type (oil/grease-lubricated shafts require specific consideration for the EDD exemption).
Is it possible to extend the interval beyond the traditional 5 years?
Yes: under IACS Recommendation No. 133, ships meeting the requirements can conduct two consecutive In-Water Surveys in place of the intermediate dry-docking, extending the maximum interval up to 7.5 years, with approval from both the Classification Society and the flag Administration.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

Survey in Dry Dock Tail Shaft Survey

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