PURPOSE: To enable repair construction to be performed safely further at a low cost without causing any necessity for removing sludge from the bottom of an oil hold to its outside, by filling the bottom of the oil hold with water so as to submerge the sludge in the bottom of the oil hold, when the repair construction of a tanker is performed.

CONSTITUTION: Repair construction of a tanker, when it is repaired, is performed by filling the bottom of an oil hold with water 3 so as to submerge sludge 2 in the bottom of the oil hold. By this construction, its safety further cost down can be promoted by eliminating any necessity for discharging the sludge 2 in the bottom of the hold to the outside without causing also a fire hazard even if a spark or the like by welding is dropped onto the bottom of the oil hold because the bottom part is filled with the water.