1. Annual Survey – General Condition and Safety Systems
The DNV Annual Survey is a comprehensive inspection conducted every year to assess the vessel's overall condition. Key focus areas include:
Hull and structure: Checks for corrosion, cracks, or deformations in critical areas.
Machinery: Tests main and auxiliary engines, steering systems, and electrical installations.
Safety equipment: Verifies the functionality of lifeboats, firefighting systems, and emergency generators.
Documentation: Ensures certificates (e.g., Safety Construction, Load Line) are valid.
If deficiencies are found, DNV may impose conditions of class (CoC), requiring repairs before the next survey. Failure to comply can lead to class suspension.
2. Intermediate Survey – Enhanced Structural and System Checks
Held between the second and third anniversary of the Renewal Survey, the Intermediate Survey involves deeper examinations:
Structural thickness measurements (ultrasonic testing) in ballast tanks and cargo holds.
Pressure testing of fuel and hydraulic systems to detect leaks.
Ballast water management system (BWMS) verification, ensuring compliance with IMO D-2 standards.
Additional checks on mooring equipment and hatch covers for wear and tear.
This survey ensures that wear-related issues are addressed before they escalate. Vessels over 15 years old may face stricter scrutiny.
3. Renewal Survey (Class Renewal) – Full Reassessment Every 5 Years
The Renewal Survey (formerly "Special Survey") is the most extensive inspection, required every five years to renew DNV class certification. It includes:
Complete hull inspection, including ultrasonic thickness gauging (UTG) of 30-50% of plating.
Pressure vessel and boiler examinations, including non-destructive testing (NDT).
Overhaul of propulsion systems, such as tail shaft withdrawal for inspection.
Verification of compliance with latest regulations (e.g., SOLAS, MARPOL updates).
If major defects are found, DNV may require dry-docking or extended repairs before recertification.
4. Bottom Survey – Hull Inspection Below Waterline
Conducted every 2.5 years (in conjunction with other surveys), the Bottom Survey examines underwater components:
Hull fouling and coating condition to assess biofouling and corrosion.
Propeller and rudder inspection for cracks, erosion, or misalignment.
Sea chests and valves checked for marine growth or leakage.
Cathodic protection systems (anodes) evaluated for effectiveness.
Vessels with high-risk trading patterns (e.g., frequent tropical waters) may need more frequent inspections.
5. Additional Surveys – Damage, Modifications, or System-Specific Checks
DNV may mandate ad-hoc surveys following incidents or system upgrades:
Damage Surveys: After grounding, collisions, or fire, assessing structural repairs.
Modification Surveys: Required if altering the hull, machinery, or safety systems.
Cargo System Surveys: For tankers, checks on pumps, piping, and inert gas systems.
Emergency Generator Tests: Verifying backup power functionality under load.
These ensure that any changes or repairs meet DNV standards before returning to service.
