The correct answer is C) direction towards which it flows. The set of a current refers to the direction towards which the current is flowing, not the direction from which it originates. This is a standard definition used in navigation and seamanship, as knowing the direction of the current's movement is crucial for safe passage and maneuvering of vessels. The other options are incorrect because A) velocity in knots describes the speed of the current, B) direction from which it flows is the opposite of the set, and D) estimated current is a general term that does not specifically describe the set or direction of the current.