2.22 SHIPYARD BALLAST

A ship on a ballast voyage to the shipyard for inspection or repair dry docking, has some special requirements. It must arrive at the shipyard with all cargo tanks cleaned and ventilated gas free. Slops must be minimised through careful decanting (if permitted by the ballast voyage route). The pumproom, cofferdams and engine room bilges must be thoroughly cleaned, along with any fuel tanks in which repairs will be carried out.
Ballast should be carefully inspected, as on any ballast voyage, for any sign of cargo contamination. The combustible gas indicator should be used to verify that no hydrocarbon vapours are present in any ballast tank ullage space.
For entering the drydock, the vessel may be required to arrive at a light ballast draft and a particular trim, usually less than one half meter of trim by the stern. To achieve these drafts on arrival, all weights in the ship need to be precisely known and a ballast plan carefully calculated to achieve the desired result. The required draft for entering the dock often is not sufficient to immerse the propeller. The ship will have to remain at normal ballast draft until the pilot is on board, then begin discharging ballast to reach the docking draft. As the ship becomes lighter, the speed must be reduced to prevent unacceptable vibration.
The ballast plan used for dry docking must be communicated to the owner's office for guidance of the shipyard dock master in providing extra blocks under the ballasted tanks. On arrival at the drydock, a complete sounding of all ballast, fuel and fresh water tanks must be taken and recorded. A copy of these soundings should be given to the dock master and posted in the ship's cargo/ballast control room. When drydock work is complete, it is vital that the ballast and other weights in the ship be the same as they were when the ship entered the dock. If ballast, fuel, or fresh water is removed or shifted while the ship is in drydock, it is essential that it be replaced to the original condition before the dock is flooded.