Answer
The regular classification framework consists of two main survey blocks: Periodical/Statutory Surveys (the 5-year cycle) and Machinery/Item-Specific Surveys.
The 5-Year Periodical Cycle
Annual Survey: Carried out every year within a window of 3 months before to 3 months after the anniversary date of the certificate.
Intermediate Survey: Held on either the 2nd or 3rd annual anniversary date. It includes an extended scope compared to an annual survey, with selective tank inspections.
Renewal Survey (Special Survey): Held every 5 years to completely renew the class certificate. Involves exhaustive structural thickness measurements and extensive machinery overhauls.
Bottom / Docking Survey: Minimum of two inspections of the outside of the ship's bottom in any 5-year period. The maximum interval between any two consecutive bottom surveys must not exceed 36 months. Can be an out-of-water drydock survey or an In-Water Survey (IWS) if approved.
Specialized & Occasional Surveys
Continuous Machinery Survey (CMS) / Planned Maintenance System (PMS) Audit: Machinery items are surveyed on a rolling basis over the 5-year cycle rather than opening everything at once during the Renewal Survey.
Tailshaft / Propeller Shaft Survey: Inspection of the propeller shaft, sterntube bearings, and oil seals (intervals depend on the shaft design and sealing arrangements, typically 3 to 5 years).
Boiler Survey: Inspection of the internal and external surfaces of water-tube and fire-tube boilers (typically twice in every 5-year period, with intervals not exceeding 36 months).
Occasional / Damage Survey: Triggered automatically following an accident, structural damage, machinery breakdown, or a PSC detention to verify that temporary or permanent repairs return the vessel to Class rules.