As a ship moves through the water, it drags with it a body of water called the wake. The ratio of the wake speed to the ship's speed is called __________.

Correct Answer: Option D — wake fraction

The wake fraction is the ratio of the speed of the wake to the speed of the ship. It quantifies the velocity of the water being dragged forward by the hull's friction and form resistance, which directly impacts the efficiency of the propeller operating in that disturbed flow field.