you are responsible for daily transfers of engine room bilges. You follow the sequences aft –fwd (P)-fwd(s) bilge well and you have never experienced a problem but 5/E started the transfer n first transferred forward (s) bilge well and without any problem and you join him later you find that bilge pump is not taking suction from fwd (p) and aft bilge well and then you have checked everything is normal. What is the cause?