Answer
The two most critical drydocking phases are taking the blocks during pumping down and leaving the blocks during refloating, because the ship’s support changes between buoyancy and the dock blocks and its effective stability continuously changes. As Chief Engineer, I will maintain the approved tank condition, prohibit unauthorised liquid transfer, ensure continuous communication, monitor list and leakage, and stop the operation immediately if any abnormality occurs.”
1. Taking the blocks and pumping down — most critical phase
When water is pumped out, the keel first contacts the keel blocks.
As the block reaction increases:
The ship’s effective stability reduces.
The vessel may develop a list.
Incorrect trim or tank condition can cause the ship to slip or land unevenly.
Excessive block loading can damage the hull.
During this period:
All ballast, fuel and cargo transfers must remain stopped.
Tank soundings and list must be monitored.
Dock Master’s instructions must be followed exactly.
Mooring lines must not impose excessive force.
Any unexpected list, movement, noise or abnormal block contact must be reported immediately.
Pumping must be stopped if the vessel is not landing correctly.
The critical period continues from first keel-block contact until the vessel is firmly supported by the keel and side blocks. Dry-dock stability rules specifically consider conditions from initial touchdown through normal supported operation.
2. Refloating and leaving the blocks — second most critical phase
Refloating is the reverse of docking.
As water rises:
The vessel gradually transfers from block support to buoyancy.
Stability changes continuously.
The ship may list if tank conditions have changed.
Leakage may occur through an incorrectly fitted plug, valve or sea connection.
During refloating:
No tank transfer should take place.
Check engine-room bilges, cofferdams, tanks and sea connections for leakage.
Confirm stern-tube, rudder-stock and shaft seals are tight.
Monitor draught, trim and list.
Start sea-water systems only when adequate submergence is available.
Stop flooding immediately if leakage or abnormal movement is detected.
The vessel must be fully afloat and clear of the blocks before propulsion or thrusters are used.