Pirates of the Caribbean (The Curse of the Black Pearl) - Sail Waves?
From time to time if you look behind the ships you can see the types of splash and waves a motor makes, and if my memory serves me correctly all of the ships in this movie have only sails. Because the time setting of this movie was before the invention of motors.
Clearly none of you have ever been sailing or you would know that the rudder causes waves when you're moving at a fast speed. It probably was the motor making the waves but it makes sense that the boat was.
Depending on what ship you're refering too that could be a possiblity. If you watch the making of portion of the dvd it tells you that the only real ship was the Intercepter. The other ships were barges that we're built up on.