What action must a boat's captain take if their vessel has broached?

When a boat has broached, it means that the vessel has turned sideways to the waves, making it vulnerable to being capsized or taking on water. The correct action a captain must take in this situation is to steer into the waves. This maneuver helps to regain control of the boat and prevents it from being swamped by the following waves. By heading into the waves, the boat can navigate them more safely and maintain stability, thereby reducing the risk of capsizing.

Steering into the waves allows the boat to cut through them rather than have them hit the side, which is critical for safety. The other options, while they may seem like potential responses, could worsen the situation. For instance, performing a quick turn might further destabilize the boat, dropping anchor could lead to more complications in rough waters, and signaling for help does not actively address the immediate danger caused by the broach. Therefore, steering into the waves is the necessary and safest immediate response to handle a broaching incident effectively.