Shipyards and repair yards handling ballast water
Docking of a vessel and treatment of ballast water
To enter a ship dock on even keel, a vessel uses ballast water to achieve the correct trim. This means that after docking, the Ballast Tanks are still (partly) filled with ballast water. For larger vessels, the amount of ballast water left in the ballast tanks can be many thousands of tonnes. Often, these Ballast Tanks must be drained in the dock, to enable inspection of the Ballast Tanks by classification societies. This draining usually achieved by opening of the bottom plugs.
The ballast water inside the Ballast Tanks of a docked vessel will often (usually) not meet the D2 standard of the Ballast Water Management Convention. This is the case even for vessels with a BWTU installed since, by design, the ballast water has to pass the BWTU twice to be able to meet the D2 standard. These treatment steps are carried out during intake and discharge of ballast water. This means that the ballast water inside a Ballast Tank does not meet the D2 standard, since it has only ever been treated at intake.
After the ballast water management convention is enforced in its full extent, in many countries it will not be allowed to discharge ballast water in a dock without meeting the D2 standard. With the help of the InvaSave however, the ballast water discharged through the bottom plugs in the dry dock can be treated to meet the D2 standard and pumped directly into the surface waters.
Filling of the Ballast Tanks before undocking
To enable save undocking, a vessel must again be filled with ballast water to achieve the correct trim, once floated. When the ship is in (dry) dock no water is available to fill up the Ballast Tanks via the BWTU.
However, many suppliers prescribe that the Ballast Tanks must be cleaned and free of untreated ballast water to guarantee the functionality of the BWTU. Owing to the very strict nature of the D2-standard, a contamination of a ballast tank with untreated ballast water will often lead to the inability of a vessel to meet this D2 standard during future ballast water operations.
With the help of the InvaSave the ballast tanks can be filled up with pre-certified D2-ballast water before undocking, without the risk of contamination the Ballast Tanks. In this way, there is no pre-existing condition that would risk failure of the commissioning tests, and the installed BWTU is free to perform to its expected standard.