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
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.