Why were they so close to the bridge pylon? They had half the river till the next one.
Loss of power and the anchor’s inability to do more than drag on a cleaned channel means they had no control at all. On either speed or direction.
A ship with only one propeller will go off in a direction depending on which way the propeller is turning. With no rudder acting -— boat is doomed to go round and round in open sea. In a channel, they leave the channel.