WATER COLLECTION IN DB TANK OF A DOUBLE HULL TANKER :
DB tank was readied for inspection out at sea. DB tank can be approached by a passage (vertical) provided in the aft. The man hole door was opened up and on inspection it was observed some water in the tank.It was taken for granted that it may be the unpumpable water.Cadet took sounding and it was found to be 30 cms.Ballast pump was started for deballasting, and the sounding did not come down.After observing all safety precautions, entry was made.While reaching almost to the bottom, water falling sound was heard.The team went towards the sound and observed a thin film of flow of water in the ballast exchange sytem line.
Suspected that the change over line valve on top was leaking, and same was closed properly.After that the leak stopped and the water was lowered by pumping out.This valve is normally above the loaded water line. Only during heavy swell it is possible for the water to reach this valve.After this incident, it was made as practice to check all the line valves which are not in use for proper closure.Also it was made compulsory to sound all the tanks on a daily basis.