Conditions/requirements for assigning IWS notation? Are 2 consecutive IWS permitted and what procedure, requirements and approval?

Answer

To qualify for and maintain the IWS (or equivalent notation like BIS / UWILD), the ship must be designed, fitted, and maintained with specific features allowing complete underwater assessment without dry-docking:

Hull Protection & Marking

• High-Performance Coating: High-durability, anti-fouling hull paint system suitable for extended immersion (typically designed for a minimum 5-year service life).

• Cathodic Protection: Effective impressed current cathodic protection (ICCP) system or sacrificial anodes designed for easy visual inspection and replacement afloat.

• Underwater Hull Markings: Clear visual reference markings painted on the underwater hull to assist diver/ROV orientation:

  • Transverse and longitudinal bulkheads.

  • Tank boundaries.

  • Shell openings (sea chests, discharge plugs, thruster tunnels).

  • Propeller blade numbering.

Underwater Machinery & Appendage Provisions

• Rudder System: Arrangements to measure clearances of rudder pintles and stock bearings while afloat (e.g., removable access plugs or measuring ports).

• Stern Tube & Shafting: Means to measure stern tube bearing wear-down/poker gauge readings afloat. Stern tube seals must be capable of being inspected and serviced afloat where applicable.

• Sea Chests & Strainers: Sea inlet openings must be fitted with hinged or easily removable gratings/grid plates to allow divers to inspect the internal sea chest plating and sea valves.

• Thrusters & Stabilizers: Means to check seal integrity and blade condition for bow/stern thrusters and stabilizer fins.

Documentation Onboard (IWS Manual)

• An approved In-Water Survey Plan/Manual containing structural drawings showing underwater openings, reference markings, clearance measuring points, and safety procedures.

In general rules: NO for standard 5-year dry-docking cycles, but YES under specific Extended Dry-Docking (EDD) Schemes or special Flag/Class permissions.

• Standard Rule (IACS Z3): Under ordinary class rules, a vessel must undergo two bottom inspections within every 5-year Special Survey cycle, and the interval between consecutive bottom inspections cannot exceed 36 months. Generally, one inspection is performed in dry dock (coinciding with the Special Survey every 5 years), while the intermediate inspection (at 2.5 years) may be an IWS. Thus, substituting two consecutive 5-year Special Survey dry-dockings with IWS is generally not permitted under basic rules.

• Exception (Extended Dry-Docking / EDD Scheme): For eligible general cargo, container, or passenger ships meeting strict criteria (typically under 15 years of age and non-ESP ships), Class and Flag States permit an Extended Dry-Docking Scheme (7.5-year dry-docking interval). Under EDD, two consecutive bottom surveys in the 7.5-year window are carried out as In-Water Surveys, postponing the physical dry-docking up to 7.5 years.

When a vessel with an IWS notation prepares to execute an in-water survey in lieu of dry-docking, the following procedure must be followed:

Step 1: Application & Pre-Survey Approvals

1. Flag State & Class Concurrence: Submit an application to the Classification Society and ensure the Flag Administration accepts the IWS in lieu of physical docking.

2. Class-Approved Diving / ROV Company: The underwater inspection must be carried out by a diving company formally approved as a Service Supplier by the specific Classification Society.

3. No Outstanding Conditions of Class: The vessel must be free of unresolved underwater structural damage or class recommendations that require dry-dock repair.

Step 2: Location & Environmental Conditions

• Site Requirements: The survey location must offer calm, sheltered waters with safe tidal/current conditions.

• Water Clarity: Underwater visibility must be adequate (typically >2 meters) to enable the attending surveyor to inspect structural plating clearly.

• Hull Cleanliness: The hull below the waterline must be free from heavy marine fouling. In-water hull cleaning must be conducted prior to inspection if fouled.

Step 3: Survey Execution & Protocol

• Attending Surveyor Oversight: A Class Surveyor must be present on site.

• Real-Time Video Communication: The diving/ROV team must use two-way radio communication and high-definition closed-circuit television (CCTV) allowing the Class Surveyor to monitor and direct the underwater inspection in real time.

• Master's Statement: The Master must submit a formal declaration confirming no unreported grounding, contact, or underwater hull damage occurred since the last docking.

• Physical Measurements Required Afloat:

  • Stern tube bearing wear-down.

  • Rudder stock and pintle clearances.

  • Tailshaft seal integrity inspection.

  • ICCP anode wastage assessment.

  • CCTV inspection of sea chest gratings, propeller blades, bow thruster, and hull plating.

Step 4: Reporting & Follow-Up

• The approved diving company submits a detailed report, including CCTV recordings, high-resolution photographs, and clearance records to the Class Surveyor.

• Defect Escalation: If the IWS reveals significant structural damage, severe corrosion, or worn bearings, the Surveyor will revoke the IWS acceptance for that survey and issue a Condition of Class requiring immediate dry-docking for repairs.