Dry-docking and Undocking — with and without damage
The Master's pre-docking obligation
Before entering dry dock the Master must verify the vessel is in a safe condition to dock: stability within approved limits throughout the docking sequence, tanks and compartments trimmed and loaded as directed by the dockmaster or the stability booklet's docking section, and all underwater damage or repairs disclosed to the dockmaster in writing. You carry ultimate responsibility — the dockmaster controls the dock, not the ship.
Key concepts to distinguish
Docking versus undocking stability Docking is the critical phase. As the keel touches the blocks and water is pumped down, the ship's effective metacentric height (GM) decreases — sometimes dramatically — because the keel reaction force acts like negative buoyancy. The transverse moment arm shortens. A vessel that is stable afloat can become unstable or acquire a dangerous list during this phase. Undocking is generally safer: as flooding restores waterplane, GM recovers progressively.
Critical point / critical condition The critical condition is the moment at which the ship's centre of gravity (G) is at the highest permissible position relative to the metacentre, accounting for the keel reaction. The docking stability calculation determines whether GM remains positive throughout. The Master must obtain and review this calculation before docking commences; you must be able to challenge it if figures do not match the ship's loading condition.
Normal docking versus damage docking
- Normal docking: stability is calculated for the as-loaded condition; tanks are adjusted to achieve the required trim and minimum positive GM throughout contact.
- Damage docking: a flooded compartment, structural failure, or loss of intact reserve buoyancy introduces unknown or asymmetric flooding, possible free-surface penalties, and potential for sudden list or roll once the dock is pumped down and residual free surface remains. The risk is that a partially flooded space does not behave predictably once external hydrostatic support reduces.
The Master's specific actions for damage docking
- Survey and quantify flooding before entry; cross-flood or pump as far as practicable to reduce asymmetry.
- Brief the dockmaster on all damaged compartments, estimated soundings, and any structural weakness that could affect how the hull distributes keel-block loads.
- Agree a pumping-down plan with planned pauses to check list and shore the hull if required.
- Ensure additional shoring or bilge blocks are in place before the waterplane area reduces to the point where transverse stability is marginal.
- Log all decisions and disclosures — your liability exposure is significant if undisclosed damage causes a capsize or structural collapse on the blocks.
Undocking
The Master confirms flooding sequence and flooding rate before commencement. A damage-repaired vessel must have the repair signed off by the relevant authority (flag state surveyor, classification society) before undocking. Confirm bilge systems operational, all openings closed, and carry out inclining or draught survey if the repair has materially altered the lightweight.
Certificates and surveys
Dry-docking intervals and associated surveys are prescribed by the vessel's classification society and flag state. For UK-coded yachts under the Red Ensign Group Yacht Code (REG YC Part A, which superseded LY3), the survey regime must satisfy both the MCA and the insurer. The Master does not authorise return to service unilaterally — that authority rests with the surveyor issuing the relevant certificate.