Answer
Dry docking is the process of removing a vessel from the water to inspect, maintain, and repair the underwater hull, sea valves, tailshaft, rudder, and cathodic protection systems. Under SOLAS Reg. I/10, cargo ships must undergo at least two bottom inspections within every 5-year Special Survey cycle, with the maximum interval between inspections not exceeding 36 months.
Preparation Strategy & Action Items:
- Pre-Docking Office & Yard Coordination:
- Spec Sheet Preparation: Prepare a detailed dry dock repair specification list (Sea Valves, Tailshaft, Hull Blasting/Painting, Anodes, Anchor Chains, Overhauls).
- Docking Plan Review: Verify vessel's structural plan detailing keel blocks, drain plugs, sea chests, bilge keels, transducer locations, and ballast tank arrangements.
- Engine Department Preparation:
- Fuel & Sludge Management: Minimize onboard heavy fuel oil; consolidate sludge and oily water into designated tanks for shore discharge.
- Boiler & Auxiliary Systems: Isolate main engine systems, isolate steam lines, switch to shore power/generators as per yard schedule, and drain sea water systems susceptible to freezing or blockage.
- Sea Chests & Valves: Label all sea valves, sea chest strainers, and overboard discharge valves targeted for overhaul. Ensure blanking plates and spare jointing materials are ready.
- Deck & Stability Preparation:
- Stability Requirements: Ensure vessel enters dock upright with zero list, minimal trim (usually 0.5–1.0 m stern trim to allow the stern frame to touch blocks first), and required critical GM (metacentric height) to prevent capsizing during the critical grounding phase.
- Logistical Measures: Secure all loose cargo/stores; clear anchor chain lockers; ensure hull drain plugs (bottom plugs) are identified, marked, and specialized tools/spanners are ready for removal once dry.