Questões de Concurso Militar DPC - Marinha 2006 para Praticante de Prático

Captain Crenshaw, in his book ”Naval Shiphandling”, states that “Shiphandling is the art of handling the velocities of a ship”. So, a pilot uses forces of engines, propellers, rudders, the wind and the tide, lines, tugs and anchors to control the velocities of a ship.
One of the most important sources of force on a ship is her own propeller and the pilot must understand the action of a propeller in order to be able to predict its action on ship.
A propeller produces side forces in addition to thrust along the propeller shaft. A ship can rotates to starboard or port as function of these side forces.
Pilot Antonio is studying propeller side force, on a single right-hand screw propeller, and knows that it can be broken down in four parts: following wake effect, inclination effect, helical discharge effect and shallow submergence effect. Antonio wrote the following consideration:
I) The following wake effect produces a net force tending to move the stern to right and cause the ship to veer to the port.
II) The inclination effect is net effect that tends to twist the ship to the right.
III) The shallow submergence effect tends the stern to starboard and cause the ship to veer to the left.
IV) The helical discharge effect tends to turn the ship to the right.

From the list of Antonio is correct to affirm, according to the book “Naval Shiphandling”, that:  

According to International Regulations for Preventing Collisions at Sea, 1972 – COLREG, while underway in a fog you hear a signal of three strokes of a bell, a rapid ringing of the bell, and three more strokes of the bell. This signal is made by a vessel __________.