losing power while underway is a biotch.Maneuverability is compromised at low speed. Especially in areas with tidal and river currents. The rudder must have adequate flow past it to work. I saw where, despite the accident occurring very near low tide (mostly slack tidal current), there was about a 1 knot current from astern at a relatively nearby instrumented bouy. It might be higher in the relatively narrow channel under the bridge.
JR