As the Ship Turns...

Pictured at right is CVN 77 (the USS George H. W. Bush) in a hard turn to port (left).  It nicely illustrates a phenomenon that catches a lot of first-time sailors on large naval ships by surprise: the ship leans “the wrong way” in a hard turn.

Actually, it's more complicated than that.  A large ship's motion in a turn varies as the turn progresses.  For example, suppose a ship is travelling at high speed in a straight line and then initiates a hard port turn by traversing the rudders to port.  Initially the rudders engaging with the moving water will force the bottom of the ship to starboard (right), and the top swings to port (left), as most people expect on a port turn.  However, as the ship itself swings around to port, the moving water acts with even more force against the hull – overpowering the rudder's sideways thrust and forcing the bottom of the hull to port, and the top of the ship to starboard.

I still remember the strangeness of these motions during hard turn exercises on the USS Long Beach when I was aboard in the '70s.  Things got even more squirrely in high winds and heavy seas as both of those phenomena contributed their own force vectors that caused yet other, even stranger motions...