It's 10 mph which is pretty slow as speeds go.

Slow-but-irresistible force meets movable object.

All objects are surprisingly movable when they encounter enough mass.

To your point, it is mass. Most people don't understand mass on water. At 1 knot the ship would do the exact same damage, topple the support and drop the bridge.

Motor control and rudder control in a momentumous frame of reference.