This week we pondered on two issues relating to the timing of Ballast Water Treatment Systems (BWTS) installation. One concerned how old vessels would be when they were eventually required to install BWTS to comply with US rules on ballast water discharge. The other tried to identify which tankers were affected by the IMO’s recent relaxation of its deadline for installing BWTS. The first we can answer accurately, but only partially. The second remains frustratingly elusive.