How does a ship get the in-water survey option?

flowchart LR
  A["Eligible: generally not more than 15 years, in class"] --> B["Fitted: long-life anti-fouling, hull markings, underwater access"]
  B --> C["Class assigns the IWS notation"]
  C --> D["IWS plan approved for each survey: diving or ROV company, cleaning, access"]
  D --> E["In-water bottom survey in lieu of one of the two dockings"]
  E --> F["Dry-dock for the other, or if a defect needs it"]

• IWS: the underwater parts (shell, rudder, propeller, sea chests and valves, anodes, tailshaft) examined afloat by an approved diving company or ROV with underwater TV, under the class surveyor.
• Where it fits: two bottom examinations in each 5-year special-survey period, not more than 36 months apart; one must be a dry-docking; the IWS option lets the other be done in water.
• Eligibility: generally not more than 15 years old, in class with a satisfactory history.
• Arrangements: a high-resistance anti-fouling coating, hull markings below the waterline, access to sea chests and valves, means to check rudder clearances and tailshaft wear-down in water.
• Notation and plan: the owner applies and class assigns the IWS notation; each survey runs to a plan submitted in advance (IACS Rec Z3/133): time, location, the approved diving or ROV company, hull cleaning, access; the flag accepts it in lieu of one docking.
• Limit: the ship still dry-docks for the other examination, and always if the IWS finds a defect needing dock repair.