Additional requirements

Requirements for ballast water management systems are available in DNV-RU-SHIP Pt.6 Ch.7 Sec.1. There are also additional requirements for both design and surveys depending on the type of the vessel.
M/S MERSol
M/S MERSol has one ballast, one bilge/ballast pump and eleven ballast tanks. Both pumps have priming units. Ballast pumps and valves are manually remote controlled through vessel’s integrated automation system. The level indications and alarms are also connected to I.A.S. system.
Ballast system sea water suctions are connected from sea water cross-over. Each ballast tank has a combined filling-suction branch (DN100) with a closing valve. All ballast pipes are of pipe class II. The tank venting pipes have dimension DN125 as required by the rules.

As an exception of the current rules (DNV July 2022) the two non-return valves between sea water and ballast system are missing from the return line. There are single non-return valves installed after both pumps (pumps with priming units are considered to act as non-return valves), at overboard discharge and on connection to bilge system. In addition, there are manual valves at both sides of the pumps and remote-controlled valves at sea water crossover and overboard discharge. The ballast pipe through collision bulkhead is fitted with pneumatic butterfly valve and a hand-operated butterfly valve directly at collision bulkhead with emergency operation above deck 3. According to DNV rules that should be screw-down type. The exceptions could be caused by the keel laying year of the vessel, or by the fact that original vessel M/S MERSol is based on was built with BV rules. In this case the requirement of two non-return valves would have applied in DNV rules already during keel laying date of M/S MERSol.
Even though fishing vessels don’t have to fulfill SOLAS requirements, the ballast tanks are painted as specified in IMO MSC215(82).