Why would you put three sets of pinger detectors on one ship? Given there is a clock running before the batteries in the pinger run out, would you not put three detectors on three boats and cover as much ground/sea as possible?
I wondered about that too.
My speculative guess is that one of them is to be suspended on a deep tow cable and a second one is to be deployed on an ROV. The third one may be a spare or perhaps is to be redeployed onto another vessel, such as the one which mobilised from Cyprus in a hurry, in the field.